Immune-Support Formulas: Vitamin C, Zinc, Elderberry and Mushrooms - Evidence by Ingredient

Q: What are immune-support formulas?

They are supplements that mix ingredients such as vitamin C, zinc, vitamin D, elderberry, echinacea and mushroom extracts and are sold to support the immune system. They are a product type, not a single ingredient.

Q: Can a supplement boost my immune system?

Trials measure colds, infections or blood markers, not a general boost. No source read showed a blend makes the immune system work better in a healthy, well-fed adult.

Q: Does vitamin C prevent colds?

Not in the general population. A 2013 Cochrane review found no change in how many people caught colds, though colds were slightly shorter in regular users. Runners, skiers and soldiers under extreme stress had fewer colds.

Q: Does zinc help colds?

Probably not to prevent them. A 2024 Cochrane review found a possible shortening of a cold started early, with low certainty and more side effects. It did not cover zinc mixed with other ingredients.

Q: Does elderberry help colds and flu?

Small trials reported milder symptoms, but NCCIH calls the evidence preliminary and says there is no good evidence for COVID-19. Raw elderberries are poisonous.

Q: Does echinacea help colds?

NCCIH says echinacea may slightly reduce the chance of catching a cold; it is unclear whether it shortens one. Products vary widely, and some people have allergic reactions.

Q: Does a multivitamin help prevent infections?

Trials are few and mostly not significant. A small trial found fewer infections only in people with diabetes who were likely low in nutrients, and a large trial found no significant drop in COVID-19.

Q: Do mushroom supplements boost immunity?

Two small trials of reishi beta-glucan raised blood immune cell counts, but infections were not measured. The National Cancer Institute calls the human studies small.

Q: Can I take too much by combining products?

Yes. Zinc, vitamin C and vitamin D appear in many products, and official limits exist. High zinc lowers copper absorption. Ask a pharmacist to add up everything you use.

Not applicable (a product type) · also called Immune blends, immune boosters, suplementos inmunitarios

Immune-support formulas are blends of vitamins, minerals, herbs and mushroom extracts sold to 'support' the immune system. No trial of the usual vitamin C, zinc, elderberry and mushroom mix was found, so the evidence comes from single ingredients and a few multivitamin trials, and it is mostly low-certainty. Vitamin D helps most in people who are very low. Check labels for the same nutrient in several products, and ask a doctor or pharmacist first.

General information, not medical advice. Last substantive update October 26, 2026 · Not medically reviewed. A named clinician has not signed off on this page. How this page is made

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About Immune-Support Formulas: Vitamin C, Zinc, Elderberry and Mushrooms - Evidence by Ingredient

Immune-support formulas combine several ingredients, usually vitamin C, zinc, vitamin D, elderberry, echinacea or mushroom extracts. Trials mostly tested the ingredients one at a time, with mixed or weak results, so the evidence for the blend itself is thin.

What immune-support formulas are

Immune-support formulas are dietary supplements that mix several ingredients and are sold as capsules, tablets, gummies, chewables, powders, lozenges or liquids. A 2022 systematic review says immune-health products make up approximately 10% of all US dietary supplement sales.

They are sold to healthy adults who want to stay well in cold season or during stress, and also to parents for children. NCCIH says supplement labels cannot claim to prevent any disease, but can carry claims about the structure or function of the body, which is why wording such as 'immune support' is common. The FDA says it cannot approve supplements for safety and effectiveness before they are sold.

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What is usually inside

The usual ingredients are vitamin C, zinc, vitamin D, black elderberry, echinacea and mushroom extracts such as reishi. The 2022 review also names garlic, vitamin A and vitamin E among common immune ingredients. Each has its own page on this site: see the related links for vitamin C, zinc, vitamin D, elderberry, echinacea and reishi, and the multivitamin page for general products.

Food also supplies several of them. The NHS names citrus fruit, peppers, strawberries, blackcurrants, broccoli, Brussels sprouts and potatoes for vitamin C, and oily fish, red meat, egg yolks and fortified foods for vitamin D. MedlinePlus names animal proteins, nuts, whole grains, legumes and yeast for zinc, and says plant zinc is less well absorbed. Supplements and foods are not the same thing, and no trial compared them.

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Reading the label

Check whether each ingredient has its own amount, or whether a mix is listed only as one total, because the second tells you little about how much of each is inside. Compare the amounts with every other product you use, including multivitamins and lozenges.

Labels do not always match the contents. A US government-supported method paper says makers often add more of a nutrient than the label states. A survey of 121 berry-extract supplements in Australia found only 18% stated how much anthocyanin they held, and elderberry products most often carried immune claims. See the gummies page linked below for how the form of a product can matter.

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What the research shows

No trial of the common blend (vitamin C, zinc, elderberry and mushrooms) was found. Trials of single ingredients show mixed or weak results for colds: regular vitamin C made colds slightly shorter but did not prevent them in the general population, zinc may shorten a cold started early, echinacea may help a little, and elderberry looked helpful in small trials. Vitamin D reduced respiratory infections, mostly in people who started very low.

Multivitamin trials were mostly not significant, and the one positive small trial was in people likely to be low in nutrients. Two small mushroom beta-glucan trials changed blood cell counts but did not measure infections. A children's product with vitamin D, zinc and a mushroom beta-glucan reduced infections in one trial.

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Single ingredients versus a blend

Results for vitamin C or zinc alone cannot be added up to describe a mix. The Cochrane zinc review left out zinc mixed with other minerals, vitamins or herbs. A blend can contain different forms and amounts than the trials used. This page gives no amounts to take; ask a doctor, pharmacist or dietitian about your own needs.

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At a glance

Traditional uses history, not proof

Elderberry and echinacea have long been used as home remedies for colds
Vitamins and minerals are sold as daily 'immune support'

Studied for research

'Immune support' labels, insufficient evidence
Multivitamin-mineral products and infections, low certainty
Vitamin C alone and colds, mixed
Zinc alone and colds, low certainty
Vitamin D and respiratory infections, moderate certainty
Elderberry and echinacea alone, low certainty
Mushroom beta-glucans and blood markers, very low certainty
High-dose zinc and vitamin C for COVID-19, no benefit seen

Main compounds

Vitamin C
Zinc
Vitamin D
Black elderberry
Echinacea
Reishi and oyster-mushroom beta-glucans

Common forms

Capsules and tablets
Gummies and chewables
Powders and drink mixes
Lozenges
Liquid shots and syrups

Research links: 2022 systematic review: supplement ingredients for immune health in healthy people · 2013 Cochrane review: vitamin C for colds · 2024 Cochrane review: zinc for colds · 2017 pooled analysis: vitamin D and respiratory infections · 2014 Cochrane review: echinacea for colds · 2026 trial analysis: multivitamin and COVID-19 (COSMOS) · Research Library · Genes & Biomarkers Library

What it is and its history

Accepted scientific name: Immune-support supplement formulas (blends of vitamins, minerals, herbs and mushroom extracts sold for 'immune support')
Common names: Immune support supplements (English); Immune boosters (English (marketing term)); Immune blends (English); Suplementos para apoyar el sistema inmunitario (Spanish); Fórmulas inmunitarias (Spanish)
Family or group: Multi-ingredient dietary supplement. A 2022 systematic review says immune-health products make up approximately 10% of all US dietary supplement sales.
Look-alikes and adulterants: Name: Multivitamin-mineral products; Note: A general product with many vitamins and minerals; it has its own page.; Name: Single-ingredient products; Note: Vitamin C, zinc, vitamin D, elderberry or echinacea sold alone have their own pages and their own trials.; Name: Mushroom blends and mushroom coffee; Note: A related product type with its own label-reading page.
Sustainability and conservation: Not assessed.

What is inside, and how it may work

What it contains and how those compounds act in cells and animals. Laboratory and animal mechanisms are not proven effects in people.

Main compounds

Compound	Family	Where it is concentrated	Activity studied	Level of evidence
Vitamin C (ascorbic acid)	vitamin	Not read from a source	NHS: protects cells, keeps skin, blood vessels, bones and cartilage healthy and helps wound healing; lack causes scurvy. Food sources named by the NHS: citrus fruit, peppers, strawberries, blackcurrants, broccoli, Brussels sprouts, potatoes. ^{7 30}	Human data
Zinc (gluconate, acetate, sulfate and other salts)	mineral	Not read from a source	Needed for the immune system, cell growth and wound healing (MedlinePlus). Found in animal foods, nuts, whole grains, legumes and yeast; plant zinc is less well absorbed (MedlinePlus). ^{17 24}	Human data
Vitamin D (D3 or D2)	vitamin	Not read from a source	Made in skin from sunlight; food sources named by the NHS include oily fish, red meat, egg yolks and fortified foods. Respiratory infection trials used D3 or D2. ^{16 31}	Human data
Black elderberry (Sambucus nigra)	herb (berry)	Berry Not read from a source	Preliminary evidence of milder cold and flu symptoms in small trials; raw or unripe parts are poisonous (NCCIH). ^{6 26}	Human data
Echinacea (E. purpurea, E. angustifolia, E. pallida)	herb	Varies by product Not read from a source	Mixed evidence for colds; products differ by species and plant part. ^{11 25}	Human data
Reishi (Ganoderma lucidum) beta-glucan	mushroom polysaccharide	Fruiting body or mycelium (varies by product) Not read from a source	Higher blood immune cell counts in two small trials; infections not measured. ^{3 8 28}	Human data
Pleuran (beta-glucan from Pleurotus ostreatus, oyster mushroom)	mushroom polysaccharide	Mushroom Not read from a source	Tested in one children's trial together with vitamin D and zinc. ⁹	Human data
Garlic, vitamin A and vitamin E	other ingredients	Not read from a source	Named in the 2022 review as ingredients with qualifying single-ingredient trials. Not researched further here. ⁴	Human data

Mechanisms, receptors and pathways

Target or pathway	Gene or receptor	What was found	Level
Beta-glucan sensing by immune cells	Pattern recognition receptors (as described in the trial abstracts)	The pleuran and reishi trial authors describe beta-glucans as acting on immune cells through pattern recognition receptors. This is a lab-based idea; the human trials read measured blood cells or infections in specific groups. ^{8 9}	Preclinical
Correcting a vitamin shortfall	Not applicable	In the vitamin D pooled analysis the benefit was much larger in people with very low starting blood levels, and in the multivitamin trial the one benefit was in a group likely to be low in micronutrients. This fits correcting a shortfall rather than boosting a healthy immune system. ^{16 2}	Human data
Copper absorption	Not specified in the sources read	The NHS says high zinc reduces how much copper the body can absorb. ³²	Human data

Absorption, metabolism and elimination

Bioavailability: Not compared across products in the sources read.

²⁴

Isolated compounds versus whole extracts

Trials of vitamin C, zinc, vitamin D, elderberry, echinacea and mushroom extracts were mostly of single ingredients. The Cochrane zinc review deliberately excluded zinc mixed with other minerals, vitamins or herbs. A result for one ingredient on its own cannot be added up to predict the result of a mix. Food sources also differ from pills.

Nutritional composition

Food sources are named from the NHS and MedlinePlus pages read on 2026-10-26; neither gives amounts per portion for the foods named, so no amounts are stated.

10benefits and uses looked at

33studies and sources checked

Moderate certaintybest evidence rating found

5lab markers tracked in trials

1 moderate certainty1 mixed findings6 low certainty1 very low certainty1 not enough evidence

What was looked at

The 10 benefits and uses checked for Immune-Support Formulas: Vitamin C, Zinc, Elderberry and Mushrooms - Evidence by Ingredient, each with how strong the evidence is. Tap one to open it.

'Immune support' on the label: what the research coversNot enough evidence
Multivitamin-mineral products and infectionsLow certainty
Vitamin C alone and coldsMixed findings
Zinc alone and coldsLow certainty
Elderberry alone and cold or flu symptomsLow certainty
Echinacea alone and coldsLow certainty
Vitamin D alone and respiratory infectionsModerate certainty
Mushroom extracts and immune blood markersVery low certainty
A chewable mushroom beta-glucan blend with vitamin D and zinc in childrenLow certainty
COVID-19 and high-dose vitamin C and zincLow certainty

Lab markers tracked in the studies

Catching a cold (risk)Length of a coldReported infections in multivitamin trialsBlood immune cell countsBlood vitamin D (25-hydroxyvitamin D)

What is Immune-Support Formulas: Vitamin C, Zinc, Elderberry and Mushrooms - Evidence by Ingredient good for?

What research found for this type of product and for the ingredients usually inside it. Most results are for single ingredients or for general multivitamins, because no trial of the common blend was found. Results for one ingredient cannot be added up to predict a mix.

'Immune support' on the labelNot enough evidenceA 2022 review found trials for only 8 of 27 ingredients common in immune products, all as single ingredients, and could not make firm statements. The NHS says there is little evidence that vitamin C, echinacea or garlic supplements prevent colds or speed recovery. Multivitamin-mineral products and infectionsLow certaintyOne small 2003 trial found fewer infections, but only among people with type 2 diabetes who were likely low in nutrients. A 2024 trial in 320 adults with bowel disease found no difference, and a large trial in older adults found no significant drop in COVID-19. Vitamin C alone and coldsMixed findingsA 2013 Cochrane review found regular vitamin C did not change how many people in the general community caught colds (RR 0.97), but colds were 8% shorter in adults and 14% shorter in children. No consistent effect once symptoms began. Zinc alone and coldsLow certaintyA 2024 Cochrane review of 34 trials found zinc may not prevent colds and may shorten a cold by about 2.4 days when started early, with low certainty and more side effects. Blends were left out of the review. Elderberry alone and cold or flu symptomsLow certaintyA 2019 meta-analysis of 180 people reported milder upper respiratory symptoms with black elderberry. NCCIH calls the research preliminary and says there is no good evidence for COVID-19. Echinacea alone and coldsLow certaintyA 2014 Cochrane review found no clear benefit for treating colds and a possible weak benefit from some products. NCCIH says it may slightly reduce the chance of catching a cold. Products differ widely. Vitamin D alone and respiratory infectionsModerate certaintyA pooled analysis of 25 trials (11,321 people) found fewer respiratory infections with vitamin D (OR 0.88), mainly with daily or weekly use and mainly in people whose levels were very low at the start (OR 0.30). Mushroom extracts and immune blood markersVery low certaintyTwo small trials of reishi beta-glucan found higher blood immune cell counts, in healthy adults and in children. Infections were not measured. The NCI calls human reishi studies small. A chewable mushroom beta-glucan blend in childrenLow certaintyIn one 2025 trial of 249 children with frequent infections, a pleuran product with vitamin D and zinc led to 15.2% fewer infections over 3 months than vitamin D and zinc alone. One product, one trial. COVID-19 and high-dose vitamin C and zincLow certaintyA 2021 trial of 214 outpatients found no significant shortening of symptoms with high-dose zinc, vitamin C, or both. NCCIH says there is no good evidence for elderberry for COVID-19.

Benefits, one by one

Each card is a research question, not a promise. Tap a goal to filter. Open a card to see the studies, doses and limits.

'Immune support' on the label: what the research covers

Not enough evidence

Products sold for 'immune support' make up roughly 10% of US supplement sales, according to a 2022 systematic review. That review found trials for only 8 of 27 ingredients commonly listed on such products (echinacea, elderberry, garlic, vitamins A, C, D and E, and zinc), all in single-ingredient products. The authors said the gaps stop them making firm statements. The NHS says there is little evidence that supplements such as vitamin C, echinacea or garlic prevent colds or help you get better more quickly.

2 studiesBlends combine ingredients and amounts that differ between products. …

Studies, doses and limits

What the trials found

The 2022 review pulled 39 randomised trials in children, adults and older people exposed to stressors such as air travel, hard exercise, study stress or winter weather. It judged that some studies may point to benefit, but could not give firm answers. No trial of a vitamin C, zinc, elderberry and mushroom blend was found in the sources read. The NHS common cold page (reviewed March 2024) says there is little evidence that vitamin C, echinacea or garlic supplements prevent colds or speed recovery.

Results

Not shown. There is no good evidence that a blend 'boosts' the immune system of a healthy, well-fed person; trials measure colds, infections and symptoms or blood markers.

Effect sizes as reported

No pooled effect sizes. The 2022 review gave no overall number in its abstract.

Why this rating

Insufficient: the evidence base is single ingredients with gaps, and no trial of the type of blend on shop shelves was read.

Form and dose studied

Blends combine ingredients and amounts that differ between products. Results for one ingredient or one product do not carry over to another.

Who was studied

Healthy children, adults and older people facing a stressor.

Limits

Only abstracts were read. The review covered single-ingredient products only, so it says nothing about blends.

Why researchers looked

People ask whether an immune blend does what the label suggests, and whether healthy people gain anything.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Not applicable

No single mechanism applies to a mix of ingredients. Each ingredient is described separately below.

A proposed mechanism does not show that the effect happens in people.

See the Safety tab for stacking of the same nutrient across products.

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Multivitamin-mineral products and infections

Low certainty

A few trials have tested a general multivitamin-mineral product against placebo for infections. A small 2003 trial of 130 adults found fewer reported infections with the supplement, but the authors said this came from the 51 people with type 2 diabetes, many with low micronutrient levels. A 2024 trial of 320 adults with bowel disease who were not low in vitamins found no difference. A large 2026 trial analysis of older adults found no significant drop in COVID-19.

4 studiesMultivitamin-mineral products, once daily, in the trials; contents di…

Studies, doses and limits

What the trials found

Barringer 2003 (130 adults, 1 year): 43% on the supplement reported an infection compared with 73% on placebo, and the difference came from the diabetes group (17% vs 93%). Laheij 2024 (320 adults with inflammatory bowel disease in remission on immune-lowering medicines, 24 weeks): 107 people in each group reported an infection (odds ratio 0.93, 0.56 to 1.48). COSMOS 2026 (18,205 older adults still taking pills in 2020): COVID-19 hazard ratio 0.93 (0.81 to 1.07); symptomatic COVID-19 odds ratio 0.70 (0.44 to 1.11), and 0.60 (0.37 to 0.99) only among people who took their pills as planned. A 2026 meta-analysis of 9 trials in older adults reported slightly better immune-marker scores overall and for multivitamin products, but these are lab markers, not infections.

Results

Mixed and mostly not significant. A benefit was seen in people likely to be low in micronutrients; none was seen in the well-nourished groups tested.

Effect sizes as reported

Infection reports: 43% vs 73% (diabetes subgroup 17% vs 93%). IBD trial OR 0.93 (0.56 to 1.48). COSMOS COVID-19 HR 0.93 (0.81 to 1.07). Immune-marker meta-analysis SMD 0.14.

Why this rating

Low: trials are few and small, results go both ways, the one positive trial was in a group likely to be deficient, and the key COVID-19 finding was not significant in the main analysis.

Form and dose studied

Multivitamin-mineral products, once daily, in the trials; contents differed between trials and are not compared here.

Who was studied

Adults with and without diabetes; adults with bowel disease; older adults.

Limits

Self-reported infections; subgroup results; one older-adult trial analysis that was secondary; abstracts only. Funding is not stated in any of the abstracts.

Why researchers looked

Many people take a daily multivitamin hoping to catch fewer infections.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Established nutrition

If someone is short of a vitamin or mineral, correcting that may help the immune system. That is established nutrition, not a trial result for a product.

A proposed mechanism does not show that the effect happens in people.

Multivitamins add to the vitamins in other products; see the Safety tab.

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Vitamin C alone and colds

Mixed findings

A Cochrane review of placebo-controlled trials (2013) found that regular vitamin C did not change how many people in the general community caught colds (risk ratio 0.97). Colds were somewhat shorter in regular users: by 8% in adults and 14% in children. Marathon runners, skiers and soldiers under heavy physical stress had about half as many colds in five trials. Started after symptoms began, there was no consistent effect. These are trials of vitamin C by itself, not blends.

2 studiesSupplements; food vitamin C was not tested in these trials.

Studies, doses and limits

What the trials found

The review covered 29 comparisons (11,306 people) for catching colds and 31 comparisons (9,745 colds) for length. It left out trials using under 0.2 g a day and trials without placebo. The authors concluded that routine vitamin C is not justified for the general population, but may be useful for people exposed to short bursts of severe exercise. The NHS says you should be able to get all the vitamin C you need from a varied diet, with sources such as citrus fruit, peppers, strawberries, blackcurrants, broccoli, Brussels sprouts and potatoes.

Results

Mixed. No prevention in the general community; a small shortening of colds with regular use; no consistent effect when started after symptoms began.

Effect sizes as reported

General community RR 0.97 (0.94 to 1.00). Extreme-exercise group RR 0.48 (0.35 to 0.64). Cold length: adults 8% shorter (3% to 12%), children 14% shorter (7% to 21%).

Why this rating

Mixed: well-run pooled trials, but the answer differs by group and by whether it was used before or after symptoms started. The review dates from 2013.

Form and dose studied

Supplements; food vitamin C was not tested in these trials.

Who was studied

General community; marathon runners, skiers and soldiers; children.

Limits

Published 2013; newer trials are not included. The extreme-exercise group is not like most readers.

Why researchers looked

Vitamin C is the best-known 'immune' vitamin, and is in most immune blends.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Established nutrition

Vitamin C has roles in the body including protecting cells and wound healing (NHS). Whether extra vitamin C changes cold risk is the trial question.

A proposed mechanism does not show that the effect happens in people.

Large amounts upset the stomach (NHS); see the Safety tab.

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Zinc alone and colds

Low certainty

A 2024 Cochrane review of 34 trials (8,526 people) found zinc may have little or no effect on preventing colds. Started during a cold, zinc may shorten it by about 2.4 days, but the evidence is low-certainty and trials differed a lot. Side effects were more common with zinc used for treatment. The review left out zinc mixed with other vitamins, minerals or herbs, so it says nothing about blends.

2 studiesZinc alone as lozenges, tablets, syrups, powders or nasal products; l…

Studies, doses and limits

What the trials found

Prevention trials: risk of a cold RR 0.93 (0.85 to 1.01, low certainty). Treatment trials: cold 2.37 days shorter (4.21 to 0.53 days shorter, I2 97%, low certainty). Non-serious side effects with zinc used for treatment: RR 1.34 (1.15 to 1.55). Most of the trials used lozenges (acetate, gluconate, orotate), and many were at some risk of bias. MedlinePlus separately notes zinc is in most multivitamin-mineral products and some cold lozenges.

Results

Mixed. Probably not a way to prevent colds; may shorten a cold that has started, with more side effects.

Effect sizes as reported

Prevention RR 0.93 (0.85 to 1.01). Treatment: 2.37 days shorter (4.21 to 0.53). Side effects RR 1.34 (1.15 to 1.55).

Why this rating

Low: the Cochrane authors rate the treatment result low-certainty because trials differ a great deal and most had some risk of bias.

Form and dose studied

Zinc alone as lozenges, tablets, syrups, powders or nasal products; lozenges most common.

Who was studied

Adults and children with colds; healthy volunteers for prevention.

Limits

Large differences between trials in zinc form, timing and length. Blends were excluded.

Why researchers looked

Zinc lozenges and zinc in immune blends are sold for colds.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Established nutrition

Zinc is an essential mineral needed for the immune system, cell growth, wound healing and taste and smell (MedlinePlus). Whether extra zinc shortens a cold is a separate trial question.

A proposed mechanism does not show that the effect happens in people.

More side effects; excess zinc blocks copper (see the Safety tab).

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Elderberry alone and cold or flu symptoms

Low certainty

A 2019 meta-analysis of randomised trials (180 people in total) reported fewer upper respiratory symptoms with black elderberry supplements. The abstract gives no numbers, and the NCCIH describes the research as preliminary: a small number of studies, mostly on colds and flu.

2 studiesBlack elderberry (Sambucus nigra) supplements; forms differed.

Studies, doses and limits

What the trials found

The meta-analysis covered 180 participants and looked at vaccination status and the cause of symptoms. The authors call the average effect large; the abstract does not show how large. NCCIH (November 2024) says there is not enough information to show elderberry helps with anything else, and that there is no good evidence for COVID-19.

Results

Preliminary. Possibly milder cold and flu symptoms in small trials.

Effect sizes as reported

A 'large mean effect size' is reported without numbers in the abstract.

Why this rating

Low: very small total number of people, no numbers in the abstract, and NCCIH calls the research preliminary.

Form and dose studied

Black elderberry (Sambucus nigra) supplements; forms differed.

Who was studied

People with colds or flu-like symptoms.

Limits

Only 180 people; abstract only; numbers not visible; quality of included trials was not read.

Why researchers looked

Elderberry is a leading ingredient in cold and flu products.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Not established

Not established in people in the sources read.

A proposed mechanism does not show that the effect happens in people.

Raw or unripe elderberries and other parts of the plant are poisonous; see the Safety tab.

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Echinacea alone and colds

Low certainty

A 2014 Cochrane review of 24 trials (4,631 people) did not pool its main results because the products differed so much. It found no clear benefit for treating colds, though a weak benefit from some products was possible. NCCIH (2024) says echinacea may slightly reduce the chance of catching a cold and that it is unclear whether it shortens one. A 2025 review of 9 trials in children reported fewer and shorter infections with Echinacea purpurea but also more side effects and signs of publication bias.

3 studiesMany extracts from different species and plant parts; results for one…

Studies, doses and limits

What the trials found

The Cochrane review: none of 12 prevention comparisons was significant by itself, but an after-the-fact pooling suggested a 10% to 20% lower chance of a cold. Only one of seven treatment trials showed a shorter cold. Side effects did not differ significantly. The children's review: duration SMD -0.19 (-0.30 to -0.09), infections RR 0.81 (0.75 to 0.87), antibiotic use RR 0.18 (0.13 to 0.25), side effects RR 1.38 (1.08 to 1.78). The Cochrane authors note that echinacea products differ in species, plant part and extraction.

Results

Mixed. A weak possible benefit for some products; no clear benefit for treating colds.

Effect sizes as reported

Cochrane: possible 10% to 20% relative lower cold risk (after-the-fact). Children: infections RR 0.81 (0.75 to 0.87); side effects RR 1.38 (1.08 to 1.78).

Why this rating

Low: products differ so much that results are not pooled for the main question, and the newer children's review has bias concerns.

Form and dose studied

Many extracts from different species and plant parts; results for one product do not carry over to another.

Who was studied

Adults and children with colds or at risk of colds.

Limits

Cochrane review dates from 2014; the 2025 review shows heterogeneity and possible publication bias.

Why researchers looked

Echinacea is one of the best-selling ingredients in cold products.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Preliminary mechanism

Not established in people. NCCIH says activity of echinacea extracts is influenced by soil conditions that affect the plant's bacteria.

A proposed mechanism does not show that the effect happens in people.

Allergic reactions can be severe, and there are medicine cautions; see the Safety tab.

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Vitamin D alone and respiratory infections

Moderate certainty

A large 2017 pooled analysis of 25 trials (11,321 people) found vitamin D lowered the chance of an acute respiratory infection overall (odds ratio 0.88). The benefit was seen with daily or weekly use, not with large single doses, and was much stronger in people whose blood vitamin D was very low at the start (odds ratio 0.30). Vitamin D is a common extra in immune blends.

3 studiesVitamin D3 or D2 alone, not in a blend.

Studies, doses and limits

What the trials found

The analysis used data on 10,933 participants. All participants: adjusted OR 0.88 (0.81 to 0.96). Daily or weekly without bolus doses: 0.81 (0.72 to 0.91). With bolus doses: 0.97 (0.86 to 1.10). Starting 25-hydroxyvitamin D under 25 nmol/L: 0.30 (0.17 to 0.53); at or above 25 nmol/L: 0.75 (0.60 to 0.95). No difference in serious adverse events (0.98, 0.80 to 1.20). A 2026 meta-analysis in older adults also reported lower inflammation markers with vitamin D (lab markers only).

Results

A modest benefit overall, largest in people who were very low in vitamin D.

Effect sizes as reported

Overall OR 0.88 (0.81 to 0.96); starting level under 25 nmol/L OR 0.30 (0.17 to 0.53).

Why this rating

Moderate: pooled individual data and the authors rate the evidence high quality, but the trials differ a great deal, the review dates from 2017, and most of the benefit is in people who were very low.

Form and dose studied

Vitamin D3 or D2 alone, not in a blend.

Who was studied

People aged 0 to 95; strongest in those with very low vitamin D.

Limits

Published 2017; benefit depends on starting level and on how the vitamin was given; not a test of a blend.

Why researchers looked

Vitamin D is often added to immune blends, and low levels are common.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Established nutrition

The NHS says the body makes vitamin D from sunlight on the skin and that a shortfall can cause bone problems such as osteomalacia. Why vitamin D affects infections was not established in the sources read; the larger benefit in very low people fits correcting a shortfall.

A proposed mechanism does not show that the effect happens in people.

Official upper limits exist; see the Safety tab.

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Mushroom extracts and immune blood markers

Very low certainty

Two small randomised trials of reishi (Ganoderma lucidum) beta-glucan, one in healthy adults for 84 days and one in children aged 3 to 5 for 12 weeks, found higher counts of some immune cells in the blood. Neither counted infections. The National Cancer Institute describes the human reishi studies as small, from China and Japan, in people with cancer, with some people showing immune changes and some not.

3 studiesReishi beta-glucan in a supplement and in yogurt. Products from other…

Studies, doses and limits

What the trials found

Adults (18 to 55, 84 days): higher CD3+, CD4+ and CD8+ T cells, CD4/CD8 ratio, natural killer cells, immunoglobulin A and natural killer cell activity than placebo; no change in kidney or liver markers. Children (3 to 5, 12 weeks, in yogurt): higher T-cell counts; kidney and liver markers stayed normal. Both groups were symptom-free, and neither trial measured infections. NCI: the FDA has not approved reishi for cancer or any other condition.

Results

Preliminary. Blood markers moved in two small trials; fewer or milder infections were not shown.

Effect sizes as reported

Numbers are not given in the abstracts.

Why this rating

Very low: two small trials, blood markers only, no infection outcomes, sponsor not stated.

Form and dose studied

Reishi beta-glucan in a supplement and in yogurt. Products from other mushrooms are different products.

Who was studied

Healthy adults aged 18 to 55; healthy children aged 3 to 5.

Limits

A higher cell count does not show better protection. Numbers of participants were not in the abstracts.

Why researchers looked

Mushroom extracts are a growing part of immune blends and 'mushroom coffee' products.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Preliminary mechanism

Beta-glucans are thought to act on immune cells through pattern recognition receptors, a lab-based idea.

A proposed mechanism does not show that the effect happens in people.

NCI says brands and batches of mushroom supplements may differ; see the Safety tab.

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A chewable mushroom beta-glucan blend with vitamin D and zinc in children

Low certainty

A 2025 trial of 249 children with frequent respiratory infections (217 finished) compared a chewable pleuran (oyster-mushroom beta-glucan) product with vitamin D and zinc against a chewable with vitamin D and zinc only. Over 3 months in cold season, the pleuran group had 15.2% fewer infections (2.35 vs 2.77). This is one of the few trials of a blend-type product. It tested the pleuran part, since both groups got vitamin D and zinc.

1 studiesA chewable pleuran product with vitamin D and zinc; do not assume oth…

Studies, doses and limits

What the trials found

Colds fell 18.6% (1.53 vs 1.88 episodes, P = 0.040). Effects were larger in children over 6. A post hoc analysis of children who started at the beginning of the season also reported fewer colds. Only mild adverse events were reported, and compliance was 98.7%.

Results

Preliminary support for one named product in children who already catch many infections.

Effect sizes as reported

Total infections 2.35 vs 2.77 (P = 0.042); colds 1.53 vs 1.88 (P = 0.040).

Why this rating

Low: a single trial of one product, some post hoc analysis, maker involvement not stated in the abstract.

Form and dose studied

A chewable pleuran product with vitamin D and zinc; do not assume other mushroom blends behave the same.

Who was studied

Children with recurrent respiratory infections in three countries.

Limits

One trial; children with frequent infections only; part post hoc; abstract only.

Why researchers looked

Parents of children with frequent colds look for blend products for children.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Preliminary mechanism

Pleuran is a beta-glucan thought to act on immune cells, a lab-based idea.

A proposed mechanism does not show that the effect happens in people.

Children should not be given supplements without advice; see the Safety tab.

⁹

COVID-19 and high-dose vitamin C and zinc

Low certainty

In a 2021 trial of 214 outpatients with COVID-19, high-dose zinc gluconate, high-dose vitamin C, or both did not significantly shorten symptoms compared with usual care. NCCIH says there is no good evidence for elderberry for COVID-19, and that the FDA and Federal Trade Commission have acted against companies that sold elderberry products with unsupported COVID-19 claims.

3 studiesHigh-dose zinc gluconate and vitamin C singly and together; elderberr…

Studies, doses and limits

What the trials found

Days to a 50% reduction in symptoms: usual care 6.7, vitamin C 5.5, zinc 5.9, both 5.5 (P = 0.45). The study was stopped for low chance of showing a benefit, was open-label, and tested single high-dose ingredients, not a blend. The NHS (2020) adds that there is not enough evidence to support taking vitamin D solely to prevent or treat COVID-19. The multivitamin trial analysis (COSMOS) is covered under multivitamins.

Results

No benefit shown. Do not rely on supplements for COVID-19.

Effect sizes as reported

Differences between groups were not statistically significant.

Why this rating

Low: one open-label, early-stopped trial; and an authority statement that there is no good evidence for elderberry.

Form and dose studied

High-dose zinc gluconate and vitamin C singly and together; elderberry supplements.

Who was studied

Adult outpatients with confirmed COVID-19.

Limits

Open-label, stopped early, single ingredients at high doses.

Why researchers looked

Immune blends were heavily marketed during the pandemic.

Traditional use

Immune-support blends are a modern product type. Single ingredients such as elderberry and echinacea have traditional uses; that is different from showing that a blend works.

Proposed mechanism Not established

Not established.

A proposed mechanism does not show that the effect happens in people.

High-dose zinc and vitamin C carry side effect risks; see the Safety tab.

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Connections to the rest of health

How Immune-Support Formulas: Vitamin C, Zinc, Elderberry and Mushrooms - Evidence by Ingredient connects to the rest of our health knowledge graph. Every link says what kind of connection it is. A safety link (for example to the liver) is a warning, not a benefit. A study that merely mentions a topic never creates a benefit link.

Explore every connection: goals, body systems, organs, symptoms, genes

Kind of connection Connected to Search

A. Wellness goals

Connected to	Evidence status	Context	Studies
Immune Support	Not enough evidence	'Immune support' on the label: what the research covers: Products sold for 'immune support' make up roughly 10% of US supplement sales, according to a 2022 systematic review. That review found trials for only 8 of 27 ingredients commonly listed on such products (echinacea, elderberry, garlic, vitamins A, C, D and E, and zinc), all in single-ingredient products. The authors said the gaps stop them making firm statements. The NHS says there is little evidence that supplements such as vitamin C, echinacea or garlic prevent colds or help you get better more quickly.	^{4 29}
Seasonal Wellness	Not enough evidence	'Immune support' on the label: what the research covers: Products sold for 'immune support' make up roughly 10% of US supplement sales, according to a 2022 systematic review. That review found trials for only 8 of 27 ingredients commonly listed on such products (echinacea, elderberry, garlic, vitamins A, C, D and E, and zinc), all in single-ingredient products. The authors said the gaps stop them making firm statements. The NHS says there is little evidence that supplements such as vitamin C, echinacea or garlic prevent colds or help you get better more quickly.	^{4 29}
Immune Support	Low certainty	Multivitamin-mineral products and infections: A few trials have tested a general multivitamin-mineral product against placebo for infections. A small 2003 trial of 130 adults found fewer reported infections with the supplement, but the authors said this came from the 51 people with type 2 diabetes, many with low micronutrient levels. A 2024 trial of 320 adults with bowel disease who were not low in vitamins found no difference. A large 2026 trial analysis of older adults found no significant drop in COVID-19. Vitamin C alone and colds: A Cochrane review of placebo-controlled trials (2013) found that regular vitamin C did not change how many people in the general community caught colds (risk ratio 0.97). Colds were somewhat shorter in regular users: by 8% in adults and 14% in children. Marathon runners, skiers and soldiers under heavy physical stress had about half as many colds in five trials. Started after symptoms began, there was no consistent effect. These are trials of vitamin C by itself, not blends.	^{2 13 14 15 7 30 17 24 11 18 25}
Seasonal Wellness	Low certainty	Multivitamin-mineral products and infections: A few trials have tested a general multivitamin-mineral product against placebo for infections. A small 2003 trial of 130 adults found fewer reported infections with the supplement, but the authors said this came from the 51 people with type 2 diabetes, many with low micronutrient levels. A 2024 trial of 320 adults with bowel disease who were not low in vitamins found no difference. A large 2026 trial analysis of older adults found no significant drop in COVID-19. Vitamin C alone and colds: A Cochrane review of placebo-controlled trials (2013) found that regular vitamin C did not change how many people in the general community caught colds (risk ratio 0.97). Colds were somewhat shorter in regular users: by 8% in adults and 14% in children. Marathon runners, skiers and soldiers under heavy physical stress had about half as many colds in five trials. Started after symptoms began, there was no consistent effect. These are trials of vitamin C by itself, not blends.	^{2 13 14 15 7 30 17 24 11 18 25}
Immune Support	Low certainty	Elderberry alone and cold or flu symptoms: A 2019 meta-analysis of randomised trials (180 people in total) reported fewer upper respiratory symptoms with black elderberry supplements. The abstract gives no numbers, and the NCCIH describes the research as preliminary: a small number of studies, mostly on colds and flu. A chewable mushroom beta-glucan blend with vitamin D and zinc in children: A 2025 trial of 249 children with frequent respiratory infections (217 finished) compared a chewable pleuran (oyster-mushroom beta-glucan) product with vitamin D and zinc against a chewable with vitamin D and zinc only. Over 3 months in cold season, the pleuran group had 15.2% fewer infections (2.35 vs 2.77). This is one of the few trials of a blend-type product. It tested the pleuran part, since both groups got vitamin D and zinc.	^{6 26 9}
Seasonal Wellness	Low certainty	Elderberry alone and cold or flu symptoms: A 2019 meta-analysis of randomised trials (180 people in total) reported fewer upper respiratory symptoms with black elderberry supplements. The abstract gives no numbers, and the NCCIH describes the research as preliminary: a small number of studies, mostly on colds and flu. A chewable mushroom beta-glucan blend with vitamin D and zinc in children: A 2025 trial of 249 children with frequent respiratory infections (217 finished) compared a chewable pleuran (oyster-mushroom beta-glucan) product with vitamin D and zinc against a chewable with vitamin D and zinc only. Over 3 months in cold season, the pleuran group had 15.2% fewer infections (2.35 vs 2.77). This is one of the few trials of a blend-type product. It tested the pleuran part, since both groups got vitamin D and zinc.	^{6 26 9}
Immune Support	Moderate certainty	Vitamin D alone and respiratory infections: A large 2017 pooled analysis of 25 trials (11,321 people) found vitamin D lowered the chance of an acute respiratory infection overall (odds ratio 0.88). The benefit was seen with daily or weekly use, not with large single doses, and was much stronger in people whose blood vitamin D was very low at the start (odds ratio 0.30). Vitamin D is a common extra in immune blends.	^{16 15 31}
Seasonal Wellness	Moderate certainty	Vitamin D alone and respiratory infections: A large 2017 pooled analysis of 25 trials (11,321 people) found vitamin D lowered the chance of an acute respiratory infection overall (odds ratio 0.88). The benefit was seen with daily or weekly use, not with large single doses, and was much stronger in people whose blood vitamin D was very low at the start (odds ratio 0.30). Vitamin D is a common extra in immune blends.	^{16 15 31}
Immune Support	Very low certainty	Mushroom extracts and immune blood markers: Two small randomised trials of reishi (Ganoderma lucidum) beta-glucan, one in healthy adults for 84 days and one in children aged 3 to 5 for 12 weeks, found higher counts of some immune cells in the blood. Neither counted infections. The National Cancer Institute describes the human reishi studies as small, from China and Japan, in people with cancer, with some people showing immune changes and some not.	^{3 8 28}
Seasonal Wellness	Very low certainty	Mushroom extracts and immune blood markers: Two small randomised trials of reishi (Ganoderma lucidum) beta-glucan, one in healthy adults for 84 days and one in children aged 3 to 5 for 12 weeks, found higher counts of some immune cells in the blood. Neither counted infections. The National Cancer Institute describes the human reishi studies as small, from China and Japan, in people with cancer, with some people showing immune changes and some not.	^{3 8 28}
Immune Support	Low certainty	COVID-19 and high-dose vitamin C and zinc: In a 2021 trial of 214 outpatients with COVID-19, high-dose zinc gluconate, high-dose vitamin C, or both did not significantly shorten symptoms compared with usual care. NCCIH says there is no good evidence for elderberry for COVID-19, and that the FDA and Federal Trade Commission have acted against companies that sold elderberry products with unsupported COVID-19 claims.	^{21 26 31}

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Immune System	Biological association	Not enough evidence	Studied for: 'Immune support' on the label: what the research covers Studied for: Multivitamin-mineral products and infections	^{4 29 2 13 14 15 7 30 17 24 6 26 11 18 25 16 31 3 8 28 9 21}
Respiratory System	Biological association	Not enough evidence	Studied for: 'Immune support' on the label: what the research covers Studied for: Multivitamin-mineral products and infections	^{4 29 2 13 14 15 7 30 17 24 6 26 11 18 25 16 31 3 8 28 9 21}

E. Health conditions

Connected to	Kind of connection	Evidence status	Context	Studies
Common cold		Preliminary	Single ingredients have mixed or weak results for colds; no blend trial was found. Preparation or compound: Immune-support supplements	^{7 17 11}

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
Catching a cold (risk)	Biological association	Mixed findings	Measured in trials: no change in the general community. A lab change is not the same as a health benefit.	^{7 17}
Length of a cold	Biological association	Low certainty	Measured in trials: slightly shorter with regular vitamin C; possibly shorter with zinc started in a cold. A lab change is not the same as a health benefit.	^{7 17}
Reported infections in multivitamin trials	Biological association	Low certainty	Measured in trials: mixed. A lab change is not the same as a health benefit.	^{2 13}
Blood immune cell counts	Biological association	Very low certainty	Measured in trials: higher with reishi beta-glucan in two small trials. A lab change is not the same as a health benefit.	^{3 8}
Blood vitamin D (25-hydroxyvitamin D)	Biological association	Moderate certainty	Measured in trials: benefit larger when the starting level was very low. A lab change is not the same as a health benefit.	¹⁶

K. Biological pathways

Connected to	Kind of connection	Evidence status	Context	Studies
Copper	Preliminary mechanism	Human	High zinc lowers copper absorption.	³²
Common cold	Preliminary mechanism	Human	The condition most trials of the ingredients measure.	^{7 17 11}

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
Vitamin C (ascorbic acid)	Biological association	Human	NHS: protects cells, keeps skin, blood vessels, bones and cartilage healthy and helps wound healing; lack causes scurvy. Food sources named by the NHS: citrus fruit, peppers, strawberries, blackcurrants, broccoli, Brussels sprouts, potatoes.	^{7 30}
Zinc (gluconate, acetate, sulfate and other salts)	Biological association	Human	Needed for the immune system, cell growth and wound healing (MedlinePlus). Found in animal foods, nuts, whole grains, legumes and yeast; plant zinc is less well absorbed (MedlinePlus).	^{17 24}
Vitamin D (D3 or D2)	Biological association	Human	Made in skin from sunlight; food sources named by the NHS include oily fish, red meat, egg yolks and fortified foods. Respiratory infection trials used D3 or D2.	^{16 31}
Black elderberry (Sambucus nigra)	Biological association	Human	Preliminary evidence of milder cold and flu symptoms in small trials; raw or unripe parts are poisonous (NCCIH). Preparation or compound: Berry	^{6 26}
Echinacea (E. purpurea, E. angustifolia, E. pallida)	Biological association	Human	Mixed evidence for colds; products differ by species and plant part. Preparation or compound: Varies by product	^{11 25}
Reishi (Ganoderma lucidum) beta-glucan	Biological association	Human	Higher blood immune cell counts in two small trials; infections not measured. Preparation or compound: Fruiting body or mycelium (varies by product)	^{3 8 28}
Pleuran (beta-glucan from Pleurotus ostreatus, oyster mushroom)	Biological association	Human	Tested in one children's trial together with vitamin D and zinc. Preparation or compound: Mushroom	⁹
Garlic, vitamin A and vitamin E	Biological association	Human	Named in the 2022 review as ingredients with qualifying single-ingredient trials. Not researched further here.	⁴

Each connection is stored with the ingredient, the connected record, the kind of connection, the evidence status, the supporting studies, the preparation or compound involved, and a review date (last reviewed October 26, 2026).

Evidence at a glance: what changed in 1 lab markers

Tap a number to show only those markers. Counts are markers, not people.

Other1

The evidence

The research centre for Immune-Support Formulas: Vitamin C, Zinc, Elderberry and Mushrooms - Evidence by Ingredient. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.

Evidence by outcome

'Immune support' on the label: what the research covers 2 studies Not enough evidence Multivitamin-mineral products and infections 4 studies Low certainty Vitamin C alone and colds 2 studies Mixed findings Zinc alone and colds 2 studies Low certainty Elderberry alone and cold or flu symptoms 2 studies Low certainty Echinacea alone and colds 3 studies Low certainty Vitamin D alone and respiratory infections 3 studies Moderate certainty Mushroom extracts and immune blood markers 3 studies Very low certainty A chewable mushroom beta-glucan blend with vitamin D and zinc in children 1 study Low certainty COVID-19 and high-dose vitamin C and zinc 3 studies Low certainty

Bars show how many studies we found for each outcome, not how well it works. People are added up across trials only (reviews are not added, to avoid double counting).

How we rate evidence

High certainty

Several well-run trials or reviews agree; further research is unlikely to change the picture much.

Moderate certainty

Good trials point the same way, but some doubt remains.

Low certainty

Small, short or inconsistent trials. The finding could change with better research.

Very low certainty

Very little or very weak human data. Treat as a possibility only.

Mixed findings

Trials or reviews disagree with each other.

Not enough evidence

Not enough human research to say either way.

Evidence against

Good research found no benefit, or found harm.

We take the reviewers' own risk-of-bias and GRADE statements where they exist, and otherwise judge from study size, design, consistency, directness and whether a product matches what is sold. Many publications do not make evidence high. Method note: We read PubMed abstracts for the reviews, trials and product surveys cited, and the NHS, NCCIH, NCI, MedlinePlus and FDA pages. Only abstracts were read for studies. The NIH Office of Dietary Supplements vitamin C page was blocked and is marked unread.

Study library: every study we checked 33

Design Research type Year from Search

Study	Design	People	Product, dose, length	Result
Andrews 2018 Dietary Supplement Ingredient Database (DSID) and the Application of Analytically Based Estimates of Ingredient Amount to Intake Calculations. J Nutr · PMID 31505677 · DOI	Database methods paper	Multivitamin-mineral products reported in the US NHANES survey, compared with lab analysis	Multivitamin-mineral products Various · vs Label amounts vs lab-measured amounts	Makers often add more than the label says. Lab-based estimates predict amounts more than 20% above the label for several nutrients in 50% to 99% of multivitamin-mineral products: iodine and selenium in adult products, iodine and vitamins D and E in children's products, and iodine, chromium and potassium in non-prescription prenatal products. Overages over 20% of label for several nutrients in 50% to 99% of products. (Not applicable) Methods, limits and funding Outcomes: Differences between label and lab content Limitations: A statistical method paper, not a survey of every product on sale. It covers multivitamin-mineral products; immune blends with herbs were not analysed. Funding and conflicts: Authors are from US government and NIH-supported groups (research support is listed in the PubMed record). Read: abstract
Barringer 2003 Effect of a multivitamin and mineral supplement on infection and quality of life. A randomized, double-blind, placebo-controlled trial. Ann Intern Med · PMID 12614088 · DOI	Randomised controlled trial	130 Community-dwelling adults aged 45 to 64 or 65 and over, with and without type 2 diabetes (51 had diabetes), in two North Carolina primary-care clinics	Daily multivitamin and mineral supplement Tablet or capsule (not stated) 1 year · vs Placebo	Fewer people on the multivitamin reported an infection (43% vs 73%) and missed work for infection (21% vs 57%). The authors say the finding came from the participants with type 2 diabetes, who had a high rate of low micronutrient levels. Well-being scores did not differ. Infection reported: 43% with supplement vs 73% with placebo (P < 0.001). Among people with diabetes: 17% vs 93%. (P values only in the abstract) Methods, limits and funding Outcomes: Self-reported infection, infection-related absence from work, and SF-12 well-being scores Limitations: Small trial (130). Infections were self-reported. The benefit was in one subgroup (diabetes, many with low micronutrient levels), so it may not apply to well-nourished people. The authors call for a larger trial. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Chen 2023 Evaluation of Immune Modulation by beta-1,3; 1,6 D-Glucan Derived from Ganoderma lucidum in Healthy Adult Volunteers, A Randomized Controlled Trial. Foods · PMID 36766186 · DOI	Randomised controlled trial	Healthy adults aged 18 to 55	Reishi (Ganoderma lucidum) beta-glucan Beta-glucan from the mushroom (product details not in the abstract) 84 days · vs Placebo	The reishi beta-glucan group had higher counts of several T cells and natural killer cells, and higher immunoglobulin A and natural killer cell activity, than the placebo group. No change in kidney or liver markers. The trial did not count infections. Higher CD3+, CD4+, CD8+ T cells, CD4/CD8 ratio and natural killer cells; no numbers in the abstract. (Not in the abstract) Methods, limits and funding Outcomes: Blood immune cell counts, immunoglobulin A, natural killer cell activity, kidney and liver markers Limitations: Blood markers only: higher cell counts are not shown to mean fewer or milder infections. Number of participants not in the abstract. Funding is not stated in the abstract. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Crawford 2022 Select Dietary Supplement Ingredients for Preserving and Protecting the Immune System in Healthy Individuals: A Systematic Review. Nutrients · PMID 36364865 · DOI	Systematic review	39 randomised trials in children, adults and seniors facing stressors such as air travel, hard exercise, study stress or winter weather	Eight single-ingredient products: echinacea, elderberry, garlic, vitamins A, C, D and E, and zinc Various Varied by trial · vs Placebo or control	Some studies may point to benefit, but gaps in the evidence stop the authors making firm statements for these ingredients. Only 8 of 27 ingredients found in a market scan of immune products had qualifying trials. No pooled effect in the abstract. (Not given in the abstract) Methods, limits and funding Outcomes: Whether supplements preserve or protect immune health in healthy people, or help them resist or recover from a stressor Limitations: Only single-ingredient products qualified, so it says nothing about blends. Details of each trial were not read, only the abstract. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Gafner 2023 Botanical Ingredient Forensics: Detection of Attempts to Deceive Commonly Used Analytical Methods for Authenticating Herbal Dietary and Food Ingredients and Supplements. J Nat Prod · PMID 36716213 · DOI	Narrative review	Review of adulteration of herbal ingredients	Botanical extracts at risk of adulteration, including elder (Sambucus nigra) berry extracts Extracts	The review lists elder berry extract among botanical ingredients at risk of adulteration, usually for financial gain, by substitution or dilution with cheaper ingredients. No rates in the abstract. (Not applicable) Methods, limits and funding Outcomes: How ingredients are substituted, diluted or fortified, and how to detect it Limitations: The abstract names ingredients at risk but gives no rates for elderberry products. Details were not read. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Hawkins 2019 Black elderberry (Sambucus nigra) supplementation effectively treats upper respiratory symptoms: A meta-analysis of randomized, controlled clinical trials. Complement Ther Med · PMID 30670267 · DOI	Systematic review meta analysis	180 Randomised trials of people with colds or flu-like upper respiratory symptoms (180 people in total)	Black elderberry (Sambucus nigra) supplements Berry extract or syrup (forms not listed in the abstract) · vs Placebo	The authors report a large average reduction in upper respiratory symptoms with elderberry. A 'large mean effect size' (the abstract gives no number). (Not in the abstract) Methods, limits and funding Outcomes: Upper respiratory symptoms Limitations: Very small total (180 people). The abstract gives no numbers. Symptoms came from colds and flu. The authors themselves note there were no large-scale studies. NCCIH describes the research as preliminary. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Hemila 2013 Vitamin C for preventing and treating the common cold. Cochrane Database Syst Rev · PMID 23440782 · DOI	Systematic review meta analysis	11306 29 trial comparisons (11,306 people) for catching colds; 31 comparisons (9,745 colds) for cold length; 7 comparisons for vitamin C started after symptoms	Vitamin C (ascorbic acid) alone; trials using under 0.2 g a day were excluded Supplement Varied · vs Placebo	Regular vitamin C did not change how many people in the general community caught colds. Colds were slightly shorter in regular users. Started after symptoms began, there was no consistent effect. General community RR 0.97. Marathon runners, skiers and soldiers on subarctic exercises RR 0.48. Cold length reduced by 8% in adults and 14% in children. (General community RR 0.97 (0.94 to 1.00); extreme-exercise group RR 0.48 (0.35 to 0.64); adults 8% (3% to 12%); children 14% (7% to 21%)) Methods, limits and funding Outcomes: Chance of catching a cold; length and severity of colds Limitations: Published 2013, so newer trials are missing. The extreme-exercise group (598 people in five trials) is not like most readers. Vitamin C alone, not in a blend. Funding and conflicts: The abstract does not state funding. Read: abstract
Henao 2018 Randomized Clinical Trial for the Evaluation of Immune Modulation by Yogurt Enriched with beta-Glucans from Lingzhi or Reishi Medicinal Mushroom, Ganoderma lucidum (Agaricomycetes), in Children from Medellin, Colombia. Int J Med Mushrooms · PMID 30317947 · DOI	Randomised controlled trial	Symptom-free children aged 3 to 5 in Medellin, Colombia	Yogurt enriched with Ganoderma lucidum beta-glucans Beta-glucan in yogurt 12 weeks (84 days) · vs Placebo yogurt	Children given the beta-glucan yogurt had higher counts of T cells (CD3+, CD4+, CD8+) in the blood than the placebo group. It was well tolerated, with no abnormal rises in creatinine or liver enzymes. Infections were not counted. Higher T-cell counts; no numbers in the abstract. (Not in the abstract) Methods, limits and funding Outcomes: Blood lymphocyte counts, immunoglobulin A, cytokines, blood counts, kidney and liver markers Limitations: Blood markers only, in children without symptoms. The authors say longer trials are needed to see whether infections are prevented. Number of children not in the abstract. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Jesenak 2025 Novel Chewable Pleuran-Based Supplement Decreases Respiratory Tract Infections in Children: A Randomised Controlled Trial. Adv Ther · PMID 41085920 · DOI	Randomised controlled trial	249 Children with recurrent respiratory infections in Slovakia, the Czech Republic and Serbia; 217 finished (104 active, 113 placebo)	A chewable product containing pleuran (a beta-glucan from the oyster mushroom Pleurotus ostreatus) plus vitamin D and zinc Chewable product 3 months in the cold season (October to March) · vs Active placebo containing vitamin D and zinc only	Children given the pleuran product had fewer infections than those given vitamin D and zinc alone (2.35 vs 2.77 over 3 months, a 15.2% reduction). Common colds fell by 18.6%. Only mild side effects were reported. Total infections 2.35 vs 2.77 (P = 0.042); colds 1.53 vs 1.88 (P = 0.040). (P values only in the abstract) Methods, limits and funding Outcomes: Total respiratory tract infections; colds; missed school days; safety Limitations: One trial of one named product, in children who already catch many infections. Because both groups got vitamin D and zinc, the trial tests the pleuran part, not the whole mix. Part of the analysis was after the fact (post hoc). Who paid for the trial is not stated in the abstract; trials of branded products can have maker involvement. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Jiang 2019 Ascorbic Acid Supplements and Kidney Stones Incidence Among Men and Women: A systematic review and meta-analysis. Urol J · PMID 30178451 · DOI	Systematic review meta analysis	4 observational studies of people using vitamin C supplements	Vitamin C (ascorbic acid) supplements Supplement Varied · vs People not using vitamin C supplements	Kidney stones were more common in men using vitamin C supplements (OR 1.62), but not in women. Men OR 1.62; women no clear link. (Men OR 1.62 (1.09 to 2.42)) Methods, limits and funding Outcomes: Kidney stones Limitations: Only four observational studies, so it shows a link, not cause. The authors call for long-term trials. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Karsch-Volk 2014 Echinacea for preventing and treating the common cold. Cochrane Database Syst Rev · PMID 24554461 · DOI	Systematic review	4631 24 double-blind trials (4,631 people, 33 comparisons) of echinacea preparations versus placebo	Echinacea single-ingredient preparations; different species and plant parts (only seven trials used the above-ground part of E. purpurea) Various extracts and products Varied · vs Placebo	Because the trials differed so much, the authors did not pool the main results. No single prevention comparison was significant, though an after-the-fact pooling hinted at a 10% to 20% lower chance of a cold. Only one of seven treatment trials showed a shorter cold. Side effects did not differ significantly. Possible 10% to 20% relative reduction in catching a cold (after-the-fact pooling only). (Not pooled in the main analysis) Methods, limits and funding Outcomes: Number of people with at least one cold (prevention); cold length (treatment); drop-outs from side effects Limitations: Published 2014. Products differed in species, plant part and extraction. The authors note that most consumers and doctors do not realise products sold as echinacea differ in composition. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Kumkum 2026 Anthocyanin-Rich Pigment Supplements in the Australian Online Market: Sources, Labelling Practices, and Bioactivity Claims. Foods · PMID 41897712 · DOI	Market survey	121 121 anthocyanin supplements sold online in Australia, July to August 2024; bilberry, elderberry and tart cherry were most common	Berry-extract supplements, including elderberry Mostly capsules (86%)	Only 18% of products stated how much anthocyanin they contained. Extract strengths and amounts per serving varied widely (10 mg to over 1,500 mg). 69% carried health claims, and elderberry products most often emphasised immune support. Content disclosed on 18% of products; health claims on 69%. (Not applicable) Methods, limits and funding Outcomes: Labelling, content disclosure and health claims Limitations: Australian online market in 2024 only; the survey looked at labels, not at lab tests of content. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Laheij 2024 The Efficacy of an Over-the-Counter Multivitamin and Mineral Supplement to Prevent Infections in Patients With Inflammatory Bowel Disease in Remission With Immunomodulators and/or Biological Agents: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial. Inflamm Bowel Dis · PMID 37793072 · DOI	Randomised controlled trial	320 Adults with inflammatory bowel disease in remission on immune-lowering medicines, not deficient in vitamins	Daily over-the-counter multivitamin and mineral supplement 24 weeks · vs Identical-looking placebo	No difference in infections: 107 patients in each group reported one. More people in the supplement group received antibiotics (32 vs 21), not a significant difference. Infection: unadjusted OR 0.93. Antibiotics: unadjusted OR 1.61. (OR 0.93 (0.56 to 1.48); antibiotics OR 1.61 (0.88 to 2.93)) Methods, limits and funding Outcomes: Infections reported over follow-up Limitations: One centre; a special group (bowel disease on immune-lowering medicines) that may not match other people. Infections were reported by the participants. Funding and conflicts: Funding and conflicts were not stated in the abstract. Research support from a non-US government source is listed in the PubMed record. Read: abstract
Li 2026 Multivitamin supplementation and COVID-19 incidence and symptom severity in the COcoa Supplement and Multivitamin Outcomes Study (COSMOS) randomized trial. Am J Clin Nutr · PMID 42385272 · DOI	Randomised controlled trial (secondary analysis)	21442 Generally healthy older US adults in a trial run June 2015 to December 2020; 18,205 still took part and took their pills on 1 January 2020	Daily multivitamin-mineral (also tested cocoa extract in a separate comparison) Pill Trial 2015 to 2020; COVID-19 outcomes during 2020 · vs Placebo	Multivitamin did not significantly lower COVID-19 infection. A possible lower chance of symptomatic COVID-19 was seen but was not statistically significant in the main analysis; it reached significance only in an analysis of people who took their pills as planned. Infection HR 0.93. Symptomatic COVID-19 OR 0.70 (main analysis) and 0.60 (adherent people only). (HR 0.93 (0.81 to 1.07); OR 0.70 (0.44 to 1.11); per-protocol OR 0.60 (0.37 to 0.99)) Methods, limits and funding Outcomes: COVID-19 infection; symptomatic COVID-19; symptom count Limitations: A secondary analysis (COVID-19 was not the trial's main question). The symptom result rests on 338 cases and the significant figure comes from the less strict analysis. Older adults only. Trial registered as NCT02422745. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Li 2026 Effects of micronutrient supplementation on immune function in older adults: a meta-analysis. Front Immunol · PMID 42254024 · DOI	Systematic review meta analysis	Older adults; 9 randomised trials	Micronutrient supplements: vitamin D, vitamin E and multivitamin products were analysed Various Varied · vs Placebo or control	Overall immune-function markers improved slightly. The authors report that multivitamin supplements showed significant improvement in overall immune function and vitamin E the largest effect on cellular immunity. Overall SMD 0.14 for immune function; vitamin D subgroup: inflammation SMD -0.40, immune cell activity SMD 0.40. (Overall SMD 0.14 (95% CI 0.07 to 0.35) as printed in the abstract) Methods, limits and funding Outcomes: Lab markers of immune function, inflammation and antioxidant status (not infections) Limitations: Only 9 trials. Results are blood and lab markers, not fewer infections. The printed confidence interval does not centre on the estimate, so the abstract's numbers should be treated cautiously. Details by trial were not read. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Martineau 2017 Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ · PMID 28202713 · DOI	Systematic review meta analysis (individual participant data)	11321 25 randomised trials, ages 0 to 95; data from 10,933 people (96.6%)	Vitamin D3 or D2 alone Supplement Varied · vs Placebo	Vitamin D lowered the chance of an acute respiratory infection overall. The benefit was seen with daily or weekly use, not with large single doses, and was much stronger in people whose blood vitamin D was very low at the start. All participants OR 0.88. Daily or weekly without bolus doses OR 0.81. Baseline 25-hydroxyvitamin D under 25 nmol/L: OR 0.30; at or above 25 nmol/L: OR 0.75. Serious adverse events OR 0.98. (OR 0.88 (0.81 to 0.96); 0.81 (0.72 to 0.91); 0.30 (0.17 to 0.53); 0.75 (0.60 to 0.95); serious events 0.98 (0.80 to 1.20)) Methods, limits and funding Outcomes: Risk of acute respiratory infection; serious adverse events Limitations: Published 2017, so later trials are not included. Vitamin D alone, not in a blend. Large differences between trials (heterogeneity P < 0.001), although the authors rate the body of evidence as high quality. Funding and conflicts: Not stated in the abstract. Read: abstract
Nault 2024 Zinc for prevention and treatment of the common cold. Cochrane Database Syst Rev · PMID 38719213 · DOI	Systematic review meta analysis	8526 34 randomised trials (15 prevention, 19 treatment); 22 in adults, 12 in children	Zinc alone (lozenges, tablets, syrups, nasal products). Zinc combined with other minerals, vitamins or herbs was left out. Lozenge, tablet, syrup, capsule, powder or nasal 4.5 to 21 days for treatment; 5 to 18 months for prevention · vs Placebo	Zinc may have little or no effect on preventing colds. When started to treat a cold it may shorten it, but the evidence is low-certainty and trials differed a lot. Side effects were more common with zinc used for treatment. Prevention RR 0.93. Treatment: 2.37 days shorter. Side effects when used for treatment: RR 1.34. (Prevention RR 0.93 (0.85 to 1.01); treatment MD -2.37 days (-4.21 to -0.53), I2 97%; side effects RR 1.34 (1.15 to 1.55)) Methods, limits and funding Outcomes: Developing a cold; cold length; side effects Limitations: Low-certainty evidence for the treatment result and large differences between trials. Most trials had some risk of bias. Because zinc mixed with other ingredients was excluded, it says nothing about blends. Funding and conflicts: Authors declare no conflicts in the abstract. Read: abstract
Pham 2025 Efficacy and safety of Echinacea purpurea in treating upper respiratory infections and complications of otitis media in children: Systematic review and meta-analysis. Clin Nutr ESPEN · PMID 40311928 · DOI	Systematic review meta analysis	3169 9 randomised trials in children (1,518 given echinacea, 1,651 given placebo)	Echinacea purpurea (roots, leaves or flowers; capsules and liquid extracts) Various Varied · vs Placebo	Echinacea purpurea was linked to shorter infections, fewer infections and less antibiotic use in children, but side effects were more common, and the authors found signs of publication bias and large differences between trials. Duration SMD -0.19; infections RR 0.81; antibiotic use RR 0.18; side effects RR 1.38. (SMD -0.19 (-0.30 to -0.09); RR 0.81 (0.75 to 0.87); antibiotics RR 0.18 (0.13 to 0.25); side effects RR 1.38 (1.08 to 1.78)) Methods, limits and funding Outcomes: Upper respiratory infection length and number; antibiotic use; ear infection episodes; side effects Limitations: Products and plant parts differed; the funnel plot suggested publication bias; the authors say the safety picture remains unclear. NCCIH's echinacea page (2024) says there is not enough evidence for a clear connection in children. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Philips 2026 Analysis of 386 alternative medicinal products implicated in liver injury reveal clinically relevant associations with potentially hepatotoxic botanicals, pharmaceutical adulteration, heavy metal contamination, and undisclosed animal content. Front Gastroenterol (Lausanne) · PMID 41890551 · DOI	Retrospective product analysis	386 386 complementary and alternative medicine products used by 91 patients with liver problems at one hospital in South India (2021 to 2023)	Mixed herbal and alternative products Various 2021 to 2023	Many products exceeded WHO limits for mercury (34%), cadmium (25%), arsenic (21%) and lead (14%). At least one hidden drug was found in 27.7% of products. Unlabelled products predicted death. Heavy metal limits exceeded: mercury 34%, cadmium 25%, arsenic 21%, lead 14%. Hidden drug in 27.7% of products. (Not applicable) Methods, limits and funding Outcomes: Ingredient documentation, heavy metals, hidden drugs, animal-derived content Limitations: Products came from patients who already had liver injury at one hospital in India, so the figures cannot be applied to supplements sold elsewhere or to immune blends in particular. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Raclariu 2018 What's in the box? Authentication of Echinacea herbal products using DNA metabarcoding and HPTLC. Phytomedicine · PMID 29895490 · DOI	Lab survey	53 53 echinacea herbal products sold in Europe	Echinacea herbal products tested by DNA and chemical methods Various · vs Label vs lab findings	Echinacea DNA was found in 34 of the 38 products retained for the DNA test (89%). Every product showed gaps between the label and what was found, with only 43% of label ingredients matching overall. Echinacea found in 89% of the 38 retained products; ingredient match with label 43%. (Not applicable) Methods, limits and funding Outcomes: Whether the species and other plants found matched the label Limitations: European products in 2018 only; cannot be assumed to apply to other markets. DNA tests could not tell echinacea species apart. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Thomas 2021 Effect of High-Dose Zinc and Ascorbic Acid Supplementation vs Usual Care on Symptom Length and Reduction Among Ambulatory Patients With SARS-CoV-2 Infection: The COVID A to Z Randomized Clinical Trial. JAMA Netw Open · PMID 33576820 · DOI	Randomised controlled trial	214 Adults with PCR-confirmed SARS-CoV-2 infection treated as outpatients in Ohio and Florida (April to October 2020)	High-dose zinc gluconate, high-dose vitamin C (ascorbic acid), both together, or usual care Supplement Higher than usual supplement amounts (see abstract) 10 days · vs Usual care (open label, no placebo)	No significant difference between the four groups in days to a 50% symptom reduction (usual care 6.7 days, vitamin C 5.5, zinc 5.9, both 5.5; overall P = .45). The study was stopped for low chance of showing a benefit. Zinc 5.9 vs usual care 6.7 days; vitamin C 5.5; both 5.5 (not significant) (Overall P = 0.45) Methods, limits and funding Outcomes: Days to a 50% reduction in symptoms Limitations: Open-label (people knew what they were taking), stopped early. High-dose single ingredients, not a blend. Not a test of prevention. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
Tucker 2018 Unapproved Pharmaceutical Ingredients Included in Dietary Supplements Associated With US Food and Drug Administration Warnings. JAMA Netw Open · PMID 30646238 · DOI	Survey of regulator warnings	776 776 adulterated supplements named in FDA warnings from 2007 to 2016	Supplements containing undeclared drug ingredients Various 2007 to 2016	Most products were sold for sexual enhancement (45.5%), weight loss (40.9%) or muscle building (11.9%). The abstract does not list immune support as a category. Some products were named again in later warnings with new hidden ingredients. 776 products; 146 companies. (Not applicable) Methods, limits and funding Outcomes: Types of hidden drug ingredient and product categories Limitations: It covers supplements the FDA flagged, not a random sample of the market, and immune products are not singled out. It shows that hidden drugs happen, not how often in immune blends. Funding and conflicts: Funding and conflicts were not stated in the abstract. Read: abstract
s-fda-consumers FDA: Information for Consumers on Using Dietary Supplements (content current as of 2022-10-21) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-medlineplus-zinc MedlinePlus Medical Encyclopedia: Zinc in diet (review date 2025-01-21) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nccih-echinacea NCCIH: Echinacea (Last Updated November 2024) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nccih-elderberry NCCIH: Elderberry (Last Updated November 2024) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nccih-wisely NCCIH: Using Dietary Supplements Wisely (Last Updated January 2019) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nci-mushrooms National Cancer Institute PDQ: Medicinal Mushrooms (patient version) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-common-cold NHS: Common cold (page last reviewed 2024-03-22) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-vitamin-c NHS: Vitamin C (page last reviewed 2020-08-03) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-vitamin-d NHS: Vitamin D (page last reviewed 2020-08-03) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-nhs-zinc NHS: Vitamins and minerals, Others (zinc section; page last reviewed 2020-08-03) · Source	Reference database n/a			Methods, limits and funding Read: full-text
s-ods-vitamin-c NIH Office of Dietary Supplements: Vitamin C fact sheet for health professionals · Source	Reference database n/a			Methods, limits and funding Read: not-read

What we do not know yet

No trial of a vitamin C, zinc, elderberry and mushroom blend was found.
No trial showed a general immune 'boost' in healthy, well-nourished adults.
Whether common blends hold what the label says was not surveyed.
The official US upper limit for vitamin C could not be read (the NIH page was blocked).
Garlic, vitamin A and vitamin E were not researched here.
Newer vitamin C trials since 2013 were not reviewed.

How new research is added

New studies are found by a saved PubMed search and placed in a review queue before the page changes.

Lab markers

What changed in blood or saliva tests during trials. A changed number is not the same as feeling or being healthier, and we give no "normal ranges".

Other 5

●

Catching a cold (risk)

No change in the general community in trials

The share of people who get at least one cold during the study.

Mixed findings

Results and what it means

Why it was measured

To see whether regular use of an ingredient lowers the chance of a cold.

Statistical vs. clinical meaning

Neither ingredient clearly lowered cold risk in the general community.

Safety implication

None for this outcome.

Study	Result	People	Product
⁷	RR 0.97 (0.94 to 1.00) in the general community; RR 0.48 (0.35 to 0.64) in five trials of runners, skiers and soldiers	29 comparisons, 11,306 people	Vitamin C alone, regular use
¹⁷	RR 0.93 (0.85 to 1.01), low certainty	9 prevention trials, 1,449 people	Zinc alone

^{7 17}

●

Length of a cold

Slightly shorter with regular vitamin C; possibly shorter with zinc started in a cold in trials

How many days a cold lasts.

Low certainty

Results and what it means

Why it was measured

To see whether an ingredient makes colds shorter or milder.

Statistical vs. clinical meaning

Small, uncertain gains; results differ a lot between trials.

Safety implication

Zinc used for treatment had more side effects (RR 1.34).

Study	Result	People	Product
⁷	Adults 8% shorter (3% to 12%); children 14% shorter (7% to 21%)	31 comparisons, 9,745 colds	Vitamin C alone, regular use
¹⁷	Mean difference -2.37 days (-4.21 to -0.53), I2 97%, low certainty	8 treatment trials, 972 people	Zinc alone started during a cold

^{7 17}

↕

Reported infections in multivitamin trials

Mixed results in trials

Whether people reported an infection during follow-up.

Low certainty

Results and what it means

Why it was measured

To see whether a daily multivitamin-mineral product leads to fewer infections.

Statistical vs. clinical meaning

One small trial found a drop in a likely-deficient subgroup; a larger one found none.

Safety implication

None for this outcome.

Study	Result	People	Product
²	43% vs 73% reported an infection; diabetes subgroup 17% vs 93%	130 adults, 1 year	Multivitamin-mineral vs placebo
¹³	107 of 162 vs 107 of 158 reported an infection, OR 0.93 (0.56 to 1.48)	320 adults with bowel disease, 24 weeks	Multivitamin-mineral vs placebo

^{2 13}

●

Blood immune cell counts

Higher with reishi beta-glucan in two small trials in trials

Numbers of T cells (CD3+, CD4+, CD8+) and natural killer cells in a blood sample.

Very low certainty

Results and what it means

Why it was measured

To see whether mushroom beta-glucans change the cells of the immune system.

Statistical vs. clinical meaning

A higher count is a lab change, not proof of better defence against infection.

Safety implication

Kidney and liver markers stayed normal in both trials.

Study	Result	People	Product
³	Higher CD3+, CD4+, CD8+ T cells and natural killer cells than placebo; no numbers in the abstract	Healthy adults aged 18 to 55, 84 days	Reishi beta-glucan
⁸	Higher CD3+, CD4+, CD8+ T cells than placebo; no numbers in the abstract	Healthy children aged 3 to 5, 12 weeks	Yogurt with reishi beta-glucan

^{3 8}

●

Blood vitamin D (25-hydroxyvitamin D)

Benefit larger when the starting level was very low in trials

The main vitamin D marker in blood.

Moderate certainty

Results and what it means

Why it was measured

To see who gains most from vitamin D for respiratory infections.

Statistical vs. clinical meaning

Correcting a very low level is a different aim from boosting a healthy immune system.

Safety implication

Serious adverse events did not differ (OR 0.98, 0.80 to 1.20).

Study	Result	People	Product
¹⁶	Starting level under 25 nmol/L: OR 0.30 (0.17 to 0.53); at or above 25 nmol/L: OR 0.75 (0.60 to 0.95)	Pooled data, daily or weekly use	Vitamin D alone

¹⁶

Safety

What studies and official sources say about side effects, medicines and who should check first. Each point shows what kind of evidence it comes from.

Main points to know 5

The same nutrient can add up across several products. Immune blends, multivitamins, lozenges and vitamin drinks can all contain zinc, vitamin C or vitamin D, so amounts can add up without notice. The NHS advises not taking more than 25 mg of zinc supplements a day unless a doctor advises it, because high zinc lowers copper absorption and can lead to anaemia and weaker bones. It says vitamin C supplements under 1,000 mg a day are unlikely to cause harm, and larger amounts can cause stomach pain, diarrhoea and wind. For vitamin D it gives upper limits by age and warns that too much can cause calcium to build up in the body and harm bones, kidneys and heart. These are official statements, not advice to take any amount. Ask a pharmacist to add up everything you use. Authoritative guidance ^{32 30 31 24}
Labels can understate what is inside. A US government-supported method paper says makers often add more of a nutrient than the label states. Lab-based estimates predict amounts more than 20% above the label for several nutrients in 50% to 99% of multivitamin-mineral products, for example iodine and selenium in adult products. Ingredient accuracy is also a problem for herbs: in a lab survey of 53 echinacea products sold in Europe, labelled ingredients matched what was found in only 43% of cases. These studies did not test every immune blend, so the real picture for any one product is unknown. Lab survey ^{1 20}
Hidden drug ingredients and heavy metals have been found in some supplements. The FDA named 776 supplements with undeclared drug ingredients between 2007 and 2016, mostly products sold for sexual enhancement, weight loss or muscle building. NCCIH says the same about products sold for those purposes. Immune products were not singled out in the sources read. A 2026 analysis of 386 alternative medicine products from patients with liver injury at one hospital in India found heavy metals above WHO limits in many products (mercury 34%, cadmium 25%, arsenic 21%, lead 14%) and a hidden drug in 27.7%. That sample is not typical of products sold elsewhere. Regulator warnings and product analysis ^{22 19 27}
Raw elderberry is poisonous. NCCIH says raw or unripe elderberries and other parts of the elder tree, such as leaves and stems, contain poisonous cyanide-producing substances that can cause nausea, vomiting and severe diarrhoea. Cooking removes the toxin. Large quantities may cause serious illness. Little is known about elderberry in pregnancy or breastfeeding. Authoritative guidance ²⁶
Echinacea can cause allergic reactions, which may be severe. NCCIH says some people have allergic reactions to echinacea and they may be severe. The most common side effects are stomach symptoms such as abdominal pain and nausea. In one clinical trial some children developed rashes that may have been allergic. A 2025 review of children's trials found side effects were more common with Echinacea purpurea (RR 1.38), though generally mild. Authoritative guidance and meta analysis ^{25 18}

Side effects 5

Effect	How often	Severity and recovery	Evidence
Stomach upset: nausea, vomiting, diarrhoea, cramps, wind The Cochrane zinc review also found possible, uncertain serious adverse events with zinc used for prevention (RR 1.67, 0.78 to 3.57, low certainty).	Zinc used for treatment of colds: non-serious side effects RR 1.34 (1.15 to 1.55) versus placebo.	Usually mild and short-lived The NHS says vitamin C symptoms disappear once the supplement is stopped. MedlinePlus says zinc symptoms go away shortly after stopping.	Authoritative guidance and meta analysis ^{30 24 17}
Copper shortage, anaemia and weaker bones with long-term high zinc MedlinePlus says a long-term excess of zinc can lead to copper, iron or magnesium deficiency.	No rate in the sources read.	Can be serious over time Not described in the sources read.	Authoritative guidance ^{32 24}
Kidney stones with vitamin C supplements (men) Four observational studies only, so this shows a link rather than proof of cause.	Men: OR 1.62 (1.09 to 2.42); no clear link in women.	Painful and sometimes needs treatment Not assessed.	Meta analysis of observational studies ¹⁰
Allergic reaction, rash, stomach symptoms with echinacea	Children's trials: side effects RR 1.38 (1.08 to 1.78).	Mostly mild; allergic reactions may be severe (NCCIH) Not described in the sources read.	Authoritative guidance and meta analysis ^{25 18}
Too much calcium in the body with too much vitamin D In the pooled trial analysis, serious adverse events did not differ with vitamin D (OR 0.98, 0.80 to 1.20).	No rate in the sources read.	Can weaken bones and damage kidneys and heart (NHS) Not described in the sources read.	Authoritative guidance ³¹

Liver

No liver injury from vitamin C, zinc, vitamin D, elderberry or echinacea was found in the sources read for this page. A liver-safety reference (LiverTox) was not opened. A 2026 analysis of 386 alternative medicine products from patients who already had liver injury found heavy metals and hidden drugs in many of them; it did not link the injury to immune blends. ¹⁹

How often. No frequency was found.

Monitoring. No agency monitoring advice was found.

This is a safety connection. It is not evidence that Immune-Support Formulas: Vitamin C, Zinc, Elderberry and Mushrooms - Evidence by Ingredient supports liver health.

Medicines and supplements 5

With	Why it matters	Importance	Evidence	What to do
Medicines broken down by the liver, immune-lowering medicines and caffeine (echinacea) prescription	NCCIH says the evidence is conflicting on whether echinacea interacts with some drugs processed by the liver, and there are theoretical reasons to suspect interactions with immunosuppressants and caffeine.	Not confirmed in the sources read. Treat as a precaution.	Authoritative guidance Low certainty ²⁵	Ask a pharmacist before using echinacea if you take medicine, especially medicines that lower the immune system.
Prescription and other medicines (elderberry and other herbal products) prescription	NCCIH says some herbs and medicines interact in harmful ways. No specific elderberry interaction was named.	General caution only.	Authoritative guidance Low certainty ²⁶	Talk to your doctor or pharmacist before using elderberry if you take any medicine.
Copper (long-term high zinc) nutrient	The NHS says high zinc lowers how much copper the body can absorb, which can lead to anaemia and weaker bones.	Documented in guidance; the amount that causes a problem was not given beyond the NHS 25 mg supplement limit.	Authoritative guidance Moderate certainty ^{32 24}	Add up zinc from all products and ask a pharmacist.
Antibiotics (quinolone and tetracycline types) and some bone drugs with zinc-containing blends prescription	Minerals can bind some medicines in the gut so less is absorbed. This is described on the single-ingredient zinc page; the underlying review was not re-read for this page.	Not re-checked here.	Review (not re read for this page) Very low certainty	Ask a pharmacist how far apart to take them.
Other supplements with the same nutrients (multivitamins, lozenges, vitamin drinks) supplement	Zinc, vitamin C and vitamin D appear in many products, so totals can pass official limits.	Stacking is the commonest practical risk for blends; no study of how often it happens was read.	Authoritative guidance Low certainty ^{32 30 31 24}	Make a list of every product and show it to a pharmacist.

Who should check first 5

Situation	Advice	Evidence
Pregnancy and breastfeeding	NCCIH says little is known about whether elderberry is safe in pregnancy or breastfeeding. For echinacea it says some studies suggest extracts may be possibly safe for up to 7 days in the first trimester and advises talking to a health care provider, and that little is known about breastfeeding. Blends often contain several ingredients, and the combined effect has not been studied in these sources. The NHS says to avoid liver in pregnancy for vitamin D food sources. Ask a doctor, midwife or pharmacist before any immune blend.	Authoritative guidance ^{26 25 31}
Children	The 2025 pleuran trial in children with recurrent infections reported only mild side effects, but it tested one product. NCCIH says to talk with a child's health care provider before giving echinacea, because some children in a trial developed rashes and allergic reactions might be severe. The NHS gives lower vitamin D upper limits for children than adults. Do not give a child a blend without advice from a doctor or pharmacist.	Authoritative guidance and trial ^{25 9 31}
People taking medicine or with a weak immune system	Echinacea has theoretical concerns with immune-lowering medicines (NCCIH). In the multivitamin trial of bowel-disease patients on such medicines, the supplement did not reduce infections. Ask your specialist before adding an immune blend.	Authoritative guidance and trial ^{25 13}
Allergy	People who have had an allergic reaction to echinacea should avoid it (NCCIH notes reactions can be severe). Check the full ingredient list of a blend for echinacea, mushroom extracts or any other ingredient you have reacted to.	Authoritative guidance ²⁵
History of kidney stones	A meta-analysis of observational studies linked vitamin C supplements to kidney stones in men. People who form stones should ask a doctor before taking a vitamin C supplement.	Meta analysis of observational studies ¹⁰

Overdose, product quality and regulators

Summary. Each main ingredient can cause harm in excess: zinc (stomach upset, then copper loss), vitamin C (stomach upset), vitamin D (too much calcium) and raw elderberry (cyanide-producing compounds). Blends and multiple products make it easier to go over official limits without noticing.

Animal. Not reviewed.

High dose or long term signals. NHS and MedlinePlus: long-term high zinc leads to copper (and iron or magnesium) deficiency. NHS: long-term too much vitamin D can cause calcium build-up that weakens bones and damages kidneys and heart.

Overdose response. If a child or adult has swallowed a large amount of a blend, call poison control or emergency services. MedlinePlus says zinc stomach symptoms usually appear within 3 to 10 hours.

Genotoxicity. Not researched.

Toxic or hazardous parts. Raw or unripe elderberries, leaves and stems (NCCIH).

Lab surveys show label and content problems in some multivitamin, herbal and berry products. None tested immune blends as a group.

Label overages in multivitamin-mineral products. Lab-based estimates predict amounts more than 20% above the label for several nutrients in 50% to 99% of multivitamin-mineral products reported in a US survey (iodine and selenium in adult products, for example). ¹

Echinacea product identity. In 53 European echinacea products, labelled ingredients matched what DNA tests found in only 43% of cases; echinacea was detected in 34 of 38 retained products (89%). ²⁰

Elderberry and berry extracts. A review lists elder berry extract as a botanical at risk of adulteration by substitution or dilution. A survey of 121 berry-extract supplements in Australia found only 18% stated how much anthocyanin they contained, and amounts per serving ranged from 10 mg to over 1,500 mg. ^{5 12}

Mushroom supplements. NCI says the FDA does not regularly review how supplements are made, so batches and brands of mushroom supplements may not be the same. ²⁸

Hidden drugs and heavy metals. 776 supplements named in FDA warnings (2007 to 2016) held undeclared drugs, mostly in sexual enhancement, weight-loss and muscle-building products. A hospital study in India found heavy metals above WHO limits in many alternative products used by liver-injury patients. ^{22 19}

Body	Action	Date
NHS / UK Department of Health and Social Care (United Kingdom)	Vitamin C: says you should be able to get all you need from a varied diet, supplements under 1,000 mg a day are unlikely to cause harm, and more can cause stomach pain, diarrhoea and wind. source	2020-08-03
NHS / UK Department of Health and Social Care (United Kingdom)	Zinc: advises not to take more than 25 mg of zinc supplements a day unless a doctor advises it, because high zinc reduces copper absorption. source	2020-08-03
NHS / UK Department of Health and Social Care (United Kingdom)	Vitamin D: says adults and children 11 to 17 should not take more than 100 micrograms (4,000 IU) a day; children 1 to 10 not more than 50 micrograms (2,000 IU); infants under 12 months not more than 25 micrograms (1,000 IU). Says there is not enough evidence to support vitamin D solely to prevent or treat COVID-19. source	2020-08-03
NCCIH (US National Institutes of Health) (United States)	Elderberry: raw or unripe parts are poisonous; no good evidence for COVID-19; FDA and Federal Trade Commission have acted against companies making unsupported COVID-19 claims for elderberry products. source	2024-11-01
NCCIH (US National Institutes of Health) (United States)	Echinacea: may slightly reduce the chance of catching a cold; allergic reactions can be severe; talk to a health care provider before giving it to a child. source	2024-11-01
FDA (US Food and Drug Administration) (United States)	Under the 1994 supplement law, the FDA cannot approve dietary supplements for safety and effectiveness before they are sold, and in many cases firms can market them without notifying the FDA. source	2022-10-21
NCCIH (US National Institutes of Health) (United States)	Supplement labels cannot claim to prevent any disease, but may carry structure or function claims; the rules for making supplements are less strict than for drugs. source	2019-01-01
National Cancer Institute (US National Institutes of Health) (United States)	Says the FDA has not approved reishi as a treatment for cancer or any other condition. source

When to get medical help

A child or adult has swallowed a large amount of a blend, or a child has got into a bottle or a pack of gummies: call poison control or emergency services.
Swelling of the face, lips or throat, trouble breathing, or widespread hives after taking a product: get emergency help.
Repeated vomiting, severe diarrhoea or stomach pain after using a blend (especially raw elderberry or large amounts of zinc): get medical help.
A cold with a high temperature for more than 3 days, symptoms getting worse, shortness of breath or chest pain: see a doctor (NHS).
Yellow skin or eyes, dark urine or severe tiredness after using any herbal product: get medical help.

Stop using the product and contact a clinician or emergency service. In the US, Poison Control is 1-800-222-1222.

General information only, not medical advice. Ask a clinician or pharmacist before use, especially with medicines, in pregnancy or with a health condition. See the Natural Remedy Safety guide.

Frequently asked questions

What are immune-support formulas?

They are supplements that mix ingredients such as vitamin C, zinc, vitamin D, elderberry, echinacea and mushroom extracts and are sold to support the immune system. They are a product type, not a single ingredient.

^{4 27}

Do immune-support blends work?

No trial of the usual vitamin C, zinc, elderberry and mushroom mix was found. A 2022 review found trials for only some single ingredients and could not make firm statements.

⁴

Can a supplement boost my immune system?

Trials measure colds, infections or blood markers, not a general boost. No source read showed a blend makes the immune system work better in a healthy, well-fed adult.

^{4 29}

Does vitamin C prevent colds?

Not in the general population. A 2013 Cochrane review found no change in how many people caught colds, though colds were slightly shorter in regular users. Runners, skiers and soldiers under extreme stress had fewer colds.

⁷

Does zinc help colds?

Probably not to prevent them. A 2024 Cochrane review found a possible shortening of a cold started early, with low certainty and more side effects. It did not cover zinc mixed with other ingredients.

¹⁷

Does elderberry help colds and flu?

Small trials reported milder symptoms, but NCCIH calls the evidence preliminary and says there is no good evidence for COVID-19. Raw elderberries are poisonous.

^{6 26}

Does echinacea help colds?

NCCIH says echinacea may slightly reduce the chance of catching a cold; it is unclear whether it shortens one. Products vary widely, and some people have allergic reactions.

^{11 25}

Does a multivitamin help prevent infections?

Trials are few and mostly not significant. A small trial found fewer infections only in people with diabetes who were likely low in nutrients, and a large trial found no significant drop in COVID-19.

^{2 13 14}

Do mushroom supplements boost immunity?

Two small trials of reishi beta-glucan raised blood immune cell counts, but infections were not measured. The National Cancer Institute calls the human studies small.

^{3 8 28}

Can I take too much by combining products?

Yes. Zinc, vitamin C and vitamin D appear in many products, and official limits exist. High zinc lowers copper absorption. Ask a pharmacist to add up everything you use.

^{32 30 31}

Are immune blends safe in pregnancy or for children?

Little is known. NCCIH says little is known about elderberry in pregnancy and breastfeeding, and it advises asking a provider before giving echinacea to a child. Ask a doctor or pharmacist before any blend.

^{26 25}

Do labels match what is inside?

Not always. Lab studies found amounts above the label in many multivitamin-mineral products, and only 43% of ingredient claims matched in a survey of echinacea products. Results for any one product are unknown.

^{1 20}

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Editorial transparency

Written by: AlternativeMed editorial team. Research compiled with AI assistance, then checked against the sources listed.
Medical review: None. This page has not been reviewed by a physician or pharmacist.
First published: 2026-10-26
Last substantive update: 2026-10-26
How we research: We read PubMed abstracts for the reviews, trials and product surveys cited, and the NHS, NCCIH, NCI, MedlinePlus and FDA pages. Only abstracts were read for studies. The NIH Office of Dietary Supplements vitamin C page was blocked and is marked unread.
How we rate evidence: See "How we rate evidence" in the Evidence tab.
Independence: No product is promoted on this page. No brands or affiliate links are shown. Trials of branded products may have maker links not stated in abstracts.

Sources 33

Each source was opened and checked. Where we read only the abstract, it says so. The small numbers in the text point here.

Andrews KW, Gusev PA, McNeal M et al.. Dietary Supplement Ingredient Database (DSID) and the Application of Analytically Based Estimates of Ingredient Amount to Intake Calculations.. J Nutr. 2018. PMID 31505677. DOI 10.1093/jn/nxy092. (abstract)
Barringer TA, Kirk JK, Santaniello AC et al.. Effect of a multivitamin and mineral supplement on infection and quality of life. A randomized, double-blind, placebo-controlled trial.. Ann Intern Med. 2003. PMID 12614088. DOI 10.7326/0003-4819-138-5-200303040-00005. (abstract)
Chen SN, Nan FH, Liu MW et al.. Evaluation of Immune Modulation by beta-1,3; 1,6 D-Glucan Derived from Ganoderma lucidum in Healthy Adult Volunteers, A Randomized Controlled Trial.. Foods. 2023. PMID 36766186. DOI 10.3390/foods12030659. (abstract)
Crawford C, Brown LL, Costello RB et al.. Select Dietary Supplement Ingredients for Preserving and Protecting the Immune System in Healthy Individuals: A Systematic Review.. Nutrients. 2022. PMID 36364865. DOI 10.3390/nu14214604. (abstract)
Gafner S, Blumenthal M, Foster S et al.. Botanical Ingredient Forensics: Detection of Attempts to Deceive Commonly Used Analytical Methods for Authenticating Herbal Dietary and Food Ingredients and Supplements.. J Nat Prod. 2023. PMID 36716213. DOI 10.1021/acs.jnatprod.2c00929. (abstract)
Hawkins J, Baker C, Cherry L et al.. Black elderberry (Sambucus nigra) supplementation effectively treats upper respiratory symptoms: A meta-analysis of randomized, controlled clinical trials.. Complement Ther Med. 2019. PMID 30670267. DOI 10.1016/j.ctim.2018.12.004. (abstract)
Hemila H, Chalker E. Vitamin C for preventing and treating the common cold.. Cochrane Database Syst Rev. 2013. PMID 23440782. DOI 10.1002/14651858.CD000980.pub4. (abstract)
Henao SLD, Urrego SA, Cano AM et al.. Randomized Clinical Trial for the Evaluation of Immune Modulation by Yogurt Enriched with beta-Glucans from Lingzhi or Reishi Medicinal Mushroom, Ganoderma lucidum (Agaricomycetes), in Children from Medellin, Colombia.. Int J Med Mushrooms. 2018. PMID 30317947. DOI 10.1615/IntJMedMushrooms.2018026986. (abstract)
Jesenak M, Prokopova E, Bozensky J et al.. Novel Chewable Pleuran-Based Supplement Decreases Respiratory Tract Infections in Children: A Randomised Controlled Trial.. Adv Ther. 2025. PMID 41085920. DOI 10.1007/s12325-025-03393-3. (abstract)
Jiang K, Tang K, Liu H et al.. Ascorbic Acid Supplements and Kidney Stones Incidence Among Men and Women: A systematic review and meta-analysis.. Urol J. 2019. PMID 30178451. DOI 10.22037/uj.v0i0.4275. (abstract)
Karsch-Volk M, Barrett B, Kiefer D et al.. Echinacea for preventing and treating the common cold.. Cochrane Database Syst Rev. 2014. PMID 24554461. DOI 10.1002/14651858.CD000530.pub3. (abstract)
Kumkum R, Livingstone KM, Aston-Mourney K. Anthocyanin-Rich Pigment Supplements in the Australian Online Market: Sources, Labelling Practices, and Bioactivity Claims.. Foods. 2026. PMID 41897712. DOI 10.3390/foods15060992. (abstract)
Laheij RLH, van Knippenberg YMW, Heil ALJ et al.. The Efficacy of an Over-the-Counter Multivitamin and Mineral Supplement to Prevent Infections in Patients With Inflammatory Bowel Disease in Remission With Immunomodulators and/or Biological Agents: A Randomized, Double-Blind, Placebo-Controlled Clinical Trial.. Inflamm Bowel Dis. 2024. PMID 37793072. DOI 10.1093/ibd/izad216. (abstract)
Li J, Manson JE, Rist PM et al.. Multivitamin supplementation and COVID-19 incidence and symptom severity in the COcoa Supplement and Multivitamin Outcomes Study (COSMOS) randomized trial.. Am J Clin Nutr. 2026. PMID 42385272. DOI 10.1016/j.ajcnut.2026.101355. (abstract)
Li D, Wang T, Xiao L et al.. Effects of micronutrient supplementation on immune function in older adults: a meta-analysis.. Front Immunol. 2026. PMID 42254024. DOI 10.3389/fimmu.2026.1732861. (abstract)
Martineau AR, Jolliffe DA, Hooper RL et al.. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data.. BMJ. 2017. PMID 28202713. DOI 10.1136/bmj.i6583. (abstract)
Nault D, Machingo TA, Shipper AG et al.. Zinc for prevention and treatment of the common cold.. Cochrane Database Syst Rev. 2024. PMID 38719213. DOI 10.1002/14651858.CD014914.pub2. (abstract)
Pham TP, Vu TM, Doan PM et al.. Efficacy and safety of Echinacea purpurea in treating upper respiratory infections and complications of otitis media in children: Systematic review and meta-analysis.. Clin Nutr ESPEN. 2025. PMID 40311928. DOI 10.1016/j.clnesp.2025.04.025. (abstract)
Philips CA, Oommen TT, Theruvath AH et al.. Analysis of 386 alternative medicinal products implicated in liver injury reveal clinically relevant associations with potentially hepatotoxic botanicals, pharmaceutical adulteration, heavy metal contamination, and undisclosed animal content.. Front Gastroenterol (Lausanne). 2026. PMID 41890551. DOI 10.3389/fgstr.2026.1784785. (abstract)
Raclariu AC, Tebrencu CE, Ichim MC et al.. What's in the box? Authentication of Echinacea herbal products using DNA metabarcoding and HPTLC.. Phytomedicine. 2018. PMID 29895490. DOI 10.1016/j.phymed.2018.03.058. (abstract)
Thomas S, Patel D, Bittel B et al.. Effect of High-Dose Zinc and Ascorbic Acid Supplementation vs Usual Care on Symptom Length and Reduction Among Ambulatory Patients With SARS-CoV-2 Infection: The COVID A to Z Randomized Clinical Trial.. JAMA Netw Open. 2021. PMID 33576820. DOI 10.1001/jamanetworkopen.2021.0369. (abstract)
Tucker J, Fischer T, Upjohn L et al.. Unapproved Pharmaceutical Ingredients Included in Dietary Supplements Associated With US Food and Drug Administration Warnings.. JAMA Netw Open. 2018. PMID 30646238. DOI 10.1001/jamanetworkopen.2018.3337. (abstract)
. FDA: Information for Consumers on Using Dietary Supplements (content current as of 2022-10-21). . . (full-text)
. MedlinePlus Medical Encyclopedia: Zinc in diet (review date 2025-01-21). . . (full-text)
. NCCIH: Echinacea (Last Updated November 2024). . . (full-text)
. NCCIH: Elderberry (Last Updated November 2024). . . (full-text)
. NCCIH: Using Dietary Supplements Wisely (Last Updated January 2019). . . (full-text)
. National Cancer Institute PDQ: Medicinal Mushrooms (patient version). . . (full-text)
. NHS: Common cold (page last reviewed 2024-03-22). . . (full-text)
. NHS: Vitamin C (page last reviewed 2020-08-03). . . (full-text)
. NHS: Vitamin D (page last reviewed 2020-08-03). . . (full-text)
. NHS: Vitamins and minerals, Others (zinc section; page last reviewed 2020-08-03). . . (full-text)
. NIH Office of Dietary Supplements: Vitamin C fact sheet for health professionals. . . (not-read)

Where to buy

Check the label first. Whatever you buy, look for these:

The amount of the active ingredient per serving, not just the front-label claim
A third-party testing mark (USP, NSF or ConsumerLab)
Other ingredients and allergens
Ask a pharmacist about interactions with your medicines

Talk to a pharmacist or doctor before you start any supplement, especially if you take medicines. See the Safety tab for interactions.

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Education, not medical advice. This page is for general information. It does not diagnose or treat any condition and is not a substitute for care from a qualified health professional. Natural does not automatically mean safe. Ask a clinician or pharmacist before changing your care, especially if you take medication, are pregnant or breastfeeding, or have a health condition.