Cod liver oil

Q: What is cod liver oil?

Cod liver oil is an oil taken from the liver of cod and related fish. It supplies the omega-3 fats EPA and DHA and, unlike ordinary fish oil, large amounts of vitamins A and D. The amounts differ by product.

Q: How is cod liver oil different from fish oil?

Fish oil usually comes from the flesh of oily fish and gives EPA and DHA. Cod liver oil comes from the liver and also carries a lot of vitamin A and vitamin D. That is why it has extra cautions. Fish oil has its own page here.

Q: Does cod liver oil prevent colds or covid-19?

In a trial of 34,601 adults in Norway, cod liver oil in winter did not lower the risk of covid-19 or other respiratory infections compared with placebo. A small children's study gave a different signal but was weaker.

Q: Does cod liver oil help arthritis?

One 9-month trial found more people with rheumatoid arthritis could cut their NSAID painkillers (39% versus 10%), but arthritis activity did not change. A small older trial found no benefit for osteoarthritis. Do not change medicines without a doctor.

Q: Is cod liver oil safe in pregnancy?

The NHS says to avoid it in pregnancy and, unless a GP advises otherwise, when trying for a baby, because its vitamin A can harm an unborn baby. Ask a doctor or midwife about omega-3 options.

Q: Can cod liver oil weaken bones?

Too much vitamin A over many years may. The NHS says more than 1.5 mg a day on average, from food and supplements, may make bones more likely to fracture, and a Norwegian study linked childhood cod liver oil to lower bone density. Products differ, so read labels.

Q: Can you get too much vitamin D from it?

Yes. Too much vitamin D over a long time can raise blood calcium and harm the kidneys and heart, says the NHS. Cod liver oil adds to vitamin D from other supplements, so the total counts.

Q: What are the side effects?

NCCIH says omega-3 side effects are usually mild: bad taste, bad breath, headache, heartburn, nausea and diarrhoea. Vitamin A and D excess are the more serious risks over time.

Q: Does it interact with medicines?

Vitamin A and D from several products add up. A 2024 review found no overall extra bleeding with omega-3, but high-dose purified EPA showed a modest rise. Ask a pharmacist if you take blood thinners or retinoid medicines; retinoid interactions were not confirmed in a source read.

Cod liver oil (fish liver oil) · also called Fish liver oil, aceite de hígado de bacalao

Cod liver oil is a supplement oil that supplies the omega-3 fats EPA and DHA together with a lot of vitamins A and D. Research did not show it prevents colds or covid-19, and evidence for arthritis is thin. The main caution is vitamin A: the NHS says to avoid it in pregnancy and not to take too much over the years. Ask a doctor or pharmacist before using it.

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 Cod liver oil

Cod liver oil is a fish liver oil that supplies omega-3 plus vitamins A and D. Its trials are mostly small or observational, and the large winter trial was negative. The vitamin A and D it carries set the limits on safe use.

What cod liver oil is

Cod liver oil comes from the liver of cod and related fish. NCCIH says fish liver oils such as cod liver oil contain the omega-3 fats EPA and DHA, and also vitamins A and D in amounts that vary from product to product. The NHS says fish store vitamin A in their livers, which is why these supplements are high in it.

It is not the same as fish oil, which usually comes from the flesh of oily fish. This page covers the supplement. The food version is on the oils and fats page, and fish oil has its own page.

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What is in it

USDA data for one generic cod liver oil entry: per tablespoon (13.6 g), about 4,080 micrograms of vitamin A, 34 micrograms of vitamin D, 0.94 g of EPA and 1.49 g of DHA. Per teaspoon, about 1,350 micrograms of vitamin A and 11 micrograms of vitamin D. Real products differ, so the label matters.

For comparison, the NHS says people should not take more than 1.5 mg (1,500 micrograms) of vitamin A a day from food and supplements combined, and not more than 100 micrograms of vitamin D a day. These are regulator statements, not advice to take cod liver oil.

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What the research shows

The best-run trial, in 34,601 adults in Norway, found no effect on covid-19 or other respiratory infections. One small trial found that more people with rheumatoid arthritis could reduce their NSAID painkillers (39% versus 10%), although arthritis activity did not change. A small osteoarthritis trial found no benefit.

Links with lower odds of childhood type 1 diabetes, multiple sclerosis and depression come from observational studies in Norway and cannot show cause. Studies also link high vitamin A to bone problems. Heart results come from omega-3 capsule trials and show little or no effect on major events.

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Food, fish oil and cod liver oil

Oily fish gives omega-3 and some vitamin D without the very high vitamin A of cod liver oil. No trial read compared cod liver oil with eating fish or taking fish oil capsules. For amounts, ask a doctor, pharmacist or dietitian; this page gives no amounts to take.

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Quality of the oil

A 2004 analysis of cod liver oil supplements sold in Italy found traces of PCBs and pesticide residues, with estimated intakes below the WHO range for dioxin-like compounds. NCCIH says vitamin amounts vary by product, so reading the label matters. Oxidation and label accuracy for cod liver oil were not researched here.

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At a glance

Traditional uses history, not proof

A traditional winter source of vitamin D, used to prevent and treat rickets
Sold as a liquid or capsules for joints, immunity and general health

Studied for research

Nutrient source, high certainty
Winter infections and covid-19, evidence against
Rheumatoid arthritis medicine use, low certainty
Osteoarthritis, evidence against
Pregnancy and child development, mixed
Type 1 diabetes, multiple sclerosis and mood, very-low certainty
Bone density, a possible harm signal

Main compounds

Vitamin A (retinol)
Vitamin D
EPA (eicosapentaenoic acid)
DHA (docosahexaenoic acid)

Common forms

Liquid oil
Capsules
Flavoured liquids for children (strength varies)

Research links: 2022 BMJ trial: cod liver oil and covid-19 (34,601 adults) · 2008 trial: cod liver oil and NSAID use in rheumatoid arthritis · 2014 review: vitamin A and hip fracture · NHS: fish and shellfish, including fish liver oil · NCCIH: omega-3 supplements · Research Library · Genes & Biomarkers Library

What it is and its history

Accepted scientific name: Cod liver oil (an oil from the liver of cod and related fish; a fish liver oil)
Common names: Cod liver oil (English); Fish liver oil (English); Aceite de hígado de bacalao (Spanish)
Family or group: A fish liver oil. NCCIH and NHS group it with fish liver oils that carry vitamins A and D as well as omega-3.
Harvest and processing: Not described in the sources read.
Look-alikes and adulterants: Name: Fish oil; Note: Oil from the flesh of oily fish (such as salmon); it supplies EPA and DHA but not the large vitamin A and D. It has its own page.; Name: Krill oil and algal oil; Note: Other omega-3 oils without fish liver vitamins; they have their own pages.; Name: Cod liver oil from food; Note: The oil as a cooking-pantry food is covered on the Oils and Fats page; this page covers the supplement.
Sustainability and conservation: Not assessed.

Traditional use and history history, not clinical proof

Tradition or era	Documented use	Source
United States, traditional use	Cod liver oil was a traditional source of vitamin D and was used to prevent and treat rickets; it has also been a folk remedy valued by many families.	p21677119
Norway and other countries, traditional use	Recommended in autumn and winter to protect against vitamin D deficiency; in Norway it is described as an important dietary source of vitamin D and the omega-3 fats EPA and DHA.	p18033763

Traditional use shows how it was used. It does not show that it works or is safe today.

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
Retinol (vitamin A)	fat-soluble vitamin	Fish liver USDA entry: 30,000 micrograms RAE per 100 g, all retinol; varies by product.	Needed by the body; excess over years linked to bone fragility and, in pregnancy, birth defects. ^{26 24 15}	Human data
Vitamin D (D2 plus D3 as listed by USDA)	fat-soluble vitamin	Fish liver USDA entry: 250 micrograms (10,000 IU) per 100 g; varies by product.	Needed for calcium balance; excess raises blood calcium. ^{26 25}	Human data
EPA and DHA (long-chain omega-3 fatty acids)	omega-3 fatty acids	Fish liver oil USDA entry: EPA 6.9 g and DHA 11.0 g per 100 g; one trial oil had DHA 1,183 mg and EPA 803 mg per 10 mL.	Tested in many trials as fish oil; effects on hearts and mood are mixed. ^{26 7 1}	Human data

Mechanisms, receptors and pathways

Target or pathway	Gene or receptor	What was found	Level
Vitamin D supply	Not described in the sources read	The large winter trial gave cod liver oil as a low-dose vitamin D supplement and found no effect on infections. ²	Human data
Anti-inflammatory effects of n-3 fatty acids	Not described in the sources read	Authors of the diabetes and arthritis studies suggest anti-inflammatory effects of long-chain n-3 fatty acids as an explanation. This was not tested in the studies read, so it is a hypothesis. ^{18 5}	Hypothesis
Vitamin A and bone	Not described in the sources read	Authors of the bone-density study suggest the past high vitamin A content of cod liver oil as a possible explanation for lower bone density. Not tested directly. ⁴	Hypothesis

Absorption, metabolism and elimination

Absorption: Not described for cod liver oil in the sources read.
Distribution: Not described.
Metabolism: Not described.
Elimination: Not described.
Bioavailability: In a UK cohort, blood levels of vitamins A and D tracked supplement intake only weakly, while EPA plus DHA blood levels tracked intake more clearly.

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Isolated compounds versus whole extracts

Cod liver oil is the oil only, not the whole fish. It carries vitamins A and D that oily fish flesh does not hold in the same amounts, so it is not the same as eating fish or taking ordinary fish oil. No trial comparing cod liver oil with fish oil capsules or with eating fish was read.

Nutritional composition

Nutrient values are from USDA FoodData Central SR Legacy (April 2018), entry "Fish oil, cod liver" (FDC 173577), read 2026-10-26 from a saved local copy: per 100 g, 902 kcal, 100 g fat, vitamin A 30,000 micrograms RAE, vitamin D 250 micrograms, EPA 6.9 g, DHA 11.0 g. One tablespoon (13.6 g) is about 4,080 micrograms vitamin A, 34 micrograms vitamin D, 0.94 g EPA and 1.49 g DHA. These are food-database values for a generic oil; products differ.

11benefits and uses looked at

26studies and sources checked

High certaintybest evidence rating found

8lab markers tracked in trials

1 high certainty2 mixed findings2 low certainty4 very low certainty2 evidence against

What was looked at

The 11 benefits and uses checked for Cod liver oil, each with how strong the evidence is. Tap one to open it.

A source of vitamin A, vitamin D, EPA and DHAHigh certainty
Colds, flu-like illness and covid-19 in winterEvidence against
Rheumatoid arthritis: needing less pain medicineLow certainty
Osteoarthritis painEvidence against
Pregnancy and children's thinking skillsMixed findings
Type 1 diabetes in children (early-life use)Very low certainty
Multiple sclerosis risk (use in the teen years)Very low certainty
Bone density (a possible harm from childhood use)Very low certainty
Depression symptoms (survey link)Very low certainty
Gestational diabetes: blood sugar and inflammation markersLow certainty
Heart and circulation (evidence is from omega-3 capsule trials)Mixed findings

Lab markers tracked in the studies

Painkiller (NSAID) use in rheumatoid arthritisPositive SARS-CoV-2 testAcute respiratory infection (self-reported)Child mental processing score (Kaufman test)Forearm bone mineral densityHbA1c in gestational diabeteshs-CRP (inflammation marker)Depression symptom score (HADS)

What is Cod liver oil good for?

The main studied uses and how strong the human evidence is for each. Most results are for the oil itself, but heart results come from omega-3 capsule trials.

A source of vitamin A, vitamin D, EPA and DHAHigh certaintyCod liver oil supplies the omega-3 fats EPA and DHA together with vitamins A and D. By USDA data, one tablespoon has about 4,080 micrograms of vitamin A, 34 micrograms of vitamin D, 0.94 g of EPA and 1.49 g of DHA. NCCIH says the vitamin amounts differ from product to product. Colds, flu-like illness and covid-19 in winterEvidence againstIn 34,601 adults in Norway, cod liver oil in winter did not lower positive SARS-CoV-2 tests, serious covid-19 or other respiratory infections compared with placebo. A small 2004 children's study reported fewer upper respiratory visits, but the oil was given with a multivitamin and only two sites were compared. Rheumatoid arthritis: needing less pain medicineLow certaintyIn one 9-month trial of 97 people, 39% on cod liver oil versus 10% on placebo cut their daily NSAID painkiller use by more than 30%. Arthritis activity did not differ. This is one small trial with high dropout. Osteoarthritis painEvidence againstIn a small 1992 trial of 86 people already on NSAIDs, adding cod liver oil gave no significant benefit compared with olive oil over 24 weeks. Pregnancy and children's thinking skillsMixed findingsChildren of mothers who took cod liver oil in pregnancy and early breastfeeding scored slightly higher at age 4 (106.4 versus 102.3), but not at age 7. Because of its vitamin A, the NHS says to avoid cod liver oil in pregnancy. Type 1 diabetes in children (early-life use)Very low certaintyTwo Norwegian case-control studies linked cod liver oil to lower odds of childhood type 1 diabetes, but they disagree on whether the link is with mothers' use in pregnancy or the child's use in the first year. Observational only. Multiple sclerosis risk (use in the teen years)Very low certaintyA Norwegian case-control study found lower odds of MS in people who recalled taking cod liver oil at ages 13 to 18 (OR 0.67). Childhood use showed no link. It is based on memory and cannot show cause. Bone density (a possible harm)Very low certaintyWomen who recalled childhood cod liver oil had lower forearm bone density in a Norwegian study (OR for low density 2.3). A review links high vitamin A intake to more hip fractures. This is a caution, not a benefit. Depression symptoms (survey link)Very low certaintyIn a survey of 21,835 Norwegian adults, daily users of cod liver oil had fewer high depression scores (2.5% versus 3.8%). A snapshot like this cannot show the oil lowers depression. Gestational diabetes: blood sugar and inflammation markersLow certaintyIn one trial of 550 women, the main blood-sugar results were not significantly different, but several secondary measures were lower at 12 to 16 weeks. The NHS advises avoiding fish liver oil in pregnancy because of vitamin A. Heart and circulation (indirect evidence)Mixed findingsLarge reviews of omega-3 capsules found little or no effect on deaths or heart events, a small possible fall in coronary events, and more atrial fibrillation with higher amounts. Cod liver oil itself was not studied in these reviews.

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.

A source of vitamin A, vitamin D, EPA and DHA

High certainty

Cod liver oil is an oil from fish liver that supplies the omega-3 fats EPA and DHA together with vitamins A and D. The USDA lists one tablespoon at about 4,080 micrograms of vitamin A, 34 micrograms of vitamin D, 0.94 g of EPA and 1.49 g of DHA. NCCIH says the vitamin amounts vary from product to product. In a UK cohort, cod liver oil nutrients about doubled people's median intakes.

5 studiesLiquid oil and capsules. Amounts differ by product; see the label.

Studies, doses and limits

What the trials found

The USDA entry for cod liver oil (one generic entry, 2018 release) lists vitamin A at 30,000 micrograms per 100 g, all as retinol, and vitamin D at 250 micrograms per 100 g. NCCIH says fish liver oils contain EPA and DHA plus vitamins A and D in amounts that differ by product. The 2015 EPIC-Norfolk analysis (6,656 people) found that cod liver oil nutrients were supplemented by 15% to 33% of people and about doubled median intakes of these nutrients, and that blood levels of vitamins A and D tracked supplement intake only weakly. Fish oil capsules from the liver of other fish, or fish oil from the flesh of oily fish, do not carry the same vitamin A and D.

Results

Cod liver oil is a real source of EPA, DHA, vitamin A and vitamin D. Nutrient content is a fact about the product, not a trial result, and varies by brand.

Effect sizes as reported

No effect size applies: these are nutrient contents.

Why this rating

High that these nutrients are present (USDA, NCCIH). It is not a trial result for any health outcome.

Form and dose studied

Liquid oil and capsules. Amounts differ by product; see the label.

Who was studied

General population.

Limits

The USDA entry is a single generic record, not a specific brand. Nutrient content of products can differ.

Why researchers looked

People ask what is actually in cod liver oil and how it differs from ordinary fish oil.

Traditional use

Cod liver oil was a traditional source of vitamin D and was used to prevent and treat rickets, according to a 2010 article. In Norway it is described as an important source of vitamin D and long-chain omega-3.

Proposed mechanism Established nutrition

The oil carries fat-soluble vitamins A and D that fish store in their livers, plus EPA and DHA (NHS, NCCIH).

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

Vitamins A and D can both be harmful in excess; see the Safety tab.

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Colds, flu-like illness and covid-19 in winter

Evidence against

The largest trial (34,601 adults in Norway) found that cod liver oil in winter did not lower the risk of a positive SARS-CoV-2 test, serious covid-19, or other acute respiratory infections compared with placebo. A smaller 2004 study in young children in New York reported fewer visits for upper respiratory problems with cod liver oil plus a multivitamin, but only two sites were compared and the oil was not tested alone.

2 studiesLiquid cod liver oil providing a low vitamin D amount in the adult tr…

Studies, doses and limits

What the trials found

The BMJ 2022 trial randomised 34,601 adults in Norway (aged 18 to 75, not already taking daily vitamin D) to cod liver oil or placebo for up to 6 months in winter. Positive SARS-CoV-2 tests were 1.31% versus 1.32%. Serious covid-19 was 0.70% versus 0.58%. Any acute respiratory infection reported was 22.94% versus 22.13%. Side effects were low-grade in both groups. The 2004 children's study randomised two paediatric offices (94 children), not individual children, and gave a multivitamin as well.

Results

Large, high-quality evidence of no protective effect in adults in winter. The children's result is weak and cannot be assigned to the oil.

Effect sizes as reported

Positive SARS-CoV-2 test RR 1.00 (adjusted CI 0.82 to 1.22); serious covid-19 RR 1.20 (0.87 to 1.65); reported respiratory infection RR 1.04 (0.97 to 1.11).

Why this rating

The large trial was well designed and null on all four main outcomes. The children's study is low-quality.

Form and dose studied

Liquid cod liver oil providing a low vitamin D amount in the adult trial.

Who was studied

Adults in Norway not on daily vitamin D; children aged 6 months to 5 years in New York.

Limits

One large trial, in Norway in winter during the pandemic. It cannot say what happens in people who are deficient in vitamin D.

Why researchers looked

Cod liver oil supplies vitamin D, and low vitamin D in winter has been linked to infections.

Traditional use

A folk remedy for winter illness in several cultures; a 2010 article says it is culturally valued by many low-income families in the United States.

Proposed mechanism Hypothesis

Not tested in the large trial; the idea is that vitamin D supports defence against infection.

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

Only low-grade side effects were reported in the large trial.

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Rheumatoid arthritis: needing less pain medicine

Low certainty

In a 9-month trial of 97 people with rheumatoid arthritis, more people on cod liver oil than on placebo were able to cut their daily NSAID painkiller use by more than 30% (39% versus 10%). Disease activity itself did not differ. Many people dropped out, and this is one small trial.

1 studiesLiquid cod liver oil in capsule form, versus air-filled placebo capsu…

Studies, doses and limits

What the trials found

A dual-centre UK trial (Galarraga 2008) randomised 97 people with RA to 10 g a day of cod liver oil (containing 2.2 g of n-3 fatty acids) or placebo capsules for 9 months. From week 12 they were asked to reduce NSAIDs gradually. 19 of 49 (39%) on cod liver oil and 5 of 48 (10%) on placebo reduced NSAID needs by more than 30% (P = 0.002). Clinical measures of disease activity and side effects did not differ. 60% finished the study.

Results

Fewer people needed as much NSAID medicine, but RA activity itself was not better.

Effect sizes as reported

39% versus 10% had a greater than 30% NSAID reduction (P = 0.002).

Why this rating

One small randomised trial with 40% dropout; no difference in disease activity.

Form and dose studied

Liquid cod liver oil in capsule form, versus air-filled placebo capsules.

Who was studied

Adults with rheumatoid arthritis already on NSAIDs.

Limits

Small, one study. Stopping medicine must only be done with a doctor.

Why researchers looked

NSAID painkillers can harm the stomach and heart, so people look for ways to need less of them.

Traditional use

Fish oils have long been used for aching joints.

Proposed mechanism Author hypothesis

The authors point to anti-inflammatory effects of n-3 fatty acids, which this trial did not measure.

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

The trial found no difference in side effects between groups. Do not change arthritis medicines without a doctor.

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Osteoarthritis pain

Evidence against

A small 1992 trial of 86 people with osteoarthritis who were already taking NSAIDs found no significant benefit from adding cod liver oil compared with olive oil over 24 weeks.

1 studiesLiquid cod liver oil versus olive oil.

Studies, doses and limits

What the trials found

A double-blind, placebo-controlled trial in UK general practice (Stammers 1992) gave 86 people 10 mL a day of cod liver oil or olive oil as an addition to NSAIDs for 24 weeks. The abstract reports no significant benefit for pain, inflammation, or interference with activities.

Results

No benefit shown in this trial. No other osteoarthritis trial of cod liver oil was read.

Effect sizes as reported

No significant difference; no numbers in the abstract.

Why this rating

One old, small null trial; no later confirmation read.

Form and dose studied

Liquid cod liver oil versus olive oil.

Who was studied

Adults with osteoarthritis taking NSAIDs.

Limits

Old and small; the abstract gives no figures.

Why researchers looked

Cod liver oil is used for stiff and painful joints.

Traditional use

Traditional use for joint aches.

Proposed mechanism Not studied

Not tested.

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

None reported in the abstract.

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Pregnancy and children's thinking skills

Mixed findings

In a Norwegian trial, children of mothers who took cod liver oil from pregnancy week 18 to 3 months after birth scored a little higher on a mental processing test at age 4 than children of mothers given corn oil. At age 7 there was no significant difference. Vitamin A is a concern in pregnancy, so health agencies say to avoid cod liver oil supplements then.

4 studies10 mL a day of cod liver oil versus corn oil, studied in a trial with…

Studies, doses and limits

What the trials found

Helland 2003 randomised 590 pregnant women (341 took part until birth; 84 children tested at 4 years) to 10 mL a day of cod liver oil or corn oil. At 4 years, Mental Processing Composite scores were 106.4 (SD 7.4, n=48) versus 102.3 (SD 11.3, n=36). The 2008 follow-up tested 143 children at age 7 and found no significant difference in global IQ. NCCIH, summarising reviews, says the evidence on omega-3 in pregnancy for child brain development is limited. The NHS says to avoid fish liver oil supplements in pregnancy because of vitamin A.

Results

A small, early score difference that did not persist to age 7.

Effect sizes as reported

Age 4: 106.4 versus 102.3. Age 7: no significant difference.

Why this rating

A small RCT with high dropout and a corn-oil comparison, followed by a null follow-up. Reviews describe the wider evidence as limited.

Form and dose studied

10 mL a day of cod liver oil versus corn oil, studied in a trial with matched vitamin A and D amounts.

Who was studied

Pregnant and breastfeeding women in Norway and their children.

Limits

Dropout was high. Corn oil is rich in omega-6, so it is not a neutral comparison. This does not support using cod liver oil in pregnancy; the NHS advises avoiding it.

Why researchers looked

The DHA in cod liver oil helps build the baby's brain, so researchers asked whether more DHA in pregnancy helps development.

Traditional use

Cod liver oil has long been given to pregnant women in Norway; the research here uses that setting.

Proposed mechanism Author background

DHA is needed for brain growth (authors' background statement); this trial did not test how it works.

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

Vitamin A in excess can harm the unborn baby; see the Safety tab. Ask a doctor or midwife.

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Type 1 diabetes in children (early-life use)

Very low certainty

Two Norwegian case-control studies found that cod liver oil use was linked to lower odds of childhood type 1 diabetes, but they disagree on when: the 2000 study found a link with the mother's use in pregnancy, and the 2003 study found it with the child's use in the first year but not the mother's use. This is observational and cannot show that the oil prevents diabetes.

2 studiesCod liver oil taken by mothers or infants, frequency by questionnaire.

Studies, doses and limits

What the trials found

Stene 2000: 85 children with diabetes and 1,071 controls in one Norwegian county. Mothers' cod liver oil in pregnancy: unadjusted OR 0.30 (0.12 to 0.75). Cod liver oil in the first year of life: adjusted OR 0.82 (0.47 to 1.42), not significant. Stene 2003: 545 cases and 1,668 controls nationally. Cod liver oil in the first year of life: adjusted OR 0.74 (0.56 to 0.99). Maternal use in pregnancy: not associated. Other vitamin D supplements were not associated in either study.

Results

Possible lower odds, but the two studies disagree on timing and neither is a trial.

Effect sizes as reported

First-year use OR 0.74 (0.56 to 0.99) in 2003; maternal use OR 0.30 (0.12 to 0.75) in 2000.

Why this rating

Observational case-control studies using recalled use; results are inconsistent across the two studies.

Form and dose studied

Cod liver oil taken by mothers or infants, frequency by questionnaire.

Who was studied

Children in Norway.

Limits

Recall bias, confounding, and a small number of cases in the 2000 study. No trial was read.

Why researchers looked

Vitamin D and omega-3 fats have anti-inflammatory properties that might protect against type 1 diabetes.

Traditional use

Cod liver oil is routinely given to infants in Norway.

Proposed mechanism Author hypothesis

The authors suggest anti-inflammatory effects of long-chain n-3 fatty acids, or vitamin D; neither was tested.

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

Infants should only be given supplements on a doctor's or health visitor's advice; vitamin A and D can both be harmful in excess.

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Multiple sclerosis risk (use in the teen years)

Very low certainty

In a Norwegian case-control study of 953 people with multiple sclerosis (MS) and 1,717 controls, those who remembered taking cod liver oil at ages 13 to 18 had lower odds of MS (OR 0.67). Use in childhood showed no link. It is observational and based on memory.

1 studiesSelf-reported cod liver oil use.

Studies, doses and limits

What the trials found

EnvIMS Norwegian study (Cortese 2015): use at ages 13 to 18 OR 0.67 (0.52 to 0.86); childhood OR 1.01 (0.81 to 1.26); the link grew with estimated amount taken in adolescence (p trend = 0.001).

Results

Association only; no trial was read.

Effect sizes as reported

Ages 13 to 18: OR 0.67 (0.52 to 0.86).

Why this rating

Observational, memory of use many years earlier; cannot show cause.

Form and dose studied

Self-reported cod liver oil use.

Who was studied

Adults in Norway with MS and controls.

Limits

Recall bias and confounding. It does not show that cod liver oil prevents MS.

Why researchers looked

Low vitamin D has been linked to MS, and cod liver oil supplies vitamin D3.

Traditional use

Cod liver oil is a long-standing vitamin D source in Norway.

Proposed mechanism Author hypothesis

The authors relate this to vitamin D; it was not measured in this study.

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

None reported in the abstract.

Bone density (a possible harm from childhood use)

Very low certainty

In 3,052 Norwegian women aged 50 to 70, those who recalled taking cod liver oil as children had lower forearm bone density than those who did not. The authors suggest the very high vitamin A content of older products. A 2014 review of prospective studies also links high vitamin A intake to more hip fractures.

3 studiesChildhood cod liver oil (recalled); dietary and supplement vitamin A …

Studies, doses and limits

What the trials found

Forsmo 2008: women with no childhood cod liver oil had significantly higher forearm BMD; OR for low BMD 2.3 (1.4 to 3.9) for year-round use. The authors note the vitamin A content in Norwegian cod liver oil had since been cut by 75%. Wu 2014 meta-analysis (8 intake studies, 283,930 people): high vitamin A intake raised hip fracture risk (RR 1.29, 1.07 to 1.57) and retinol did too (RR 1.40, 1.03 to 1.91); beta-carotene did not; both high and low blood retinol were linked to higher hip-fracture risk. Total fractures did not differ. The NHS says long-term intake above 1.5 mg of vitamin A a day may make bones more likely to fracture.

Results

The signal is a caution, not a benefit: no trial has shown cod liver oil strengthens bones in this evidence.

Effect sizes as reported

Low BMD OR 2.3 (1.4 to 3.9); hip fracture RR 1.29 (1.07 to 1.57) for high vitamin A intake.

Why this rating

All observational. The bone studies do not measure cod liver oil alone in the meta-analysis. Today's products may contain less vitamin A.

Form and dose studied

Childhood cod liver oil (recalled); dietary and supplement vitamin A in cohorts.

Who was studied

Women aged 50 to 70 in Norway; adults in cohort studies.

Limits

Observational; vitamin A was a suggested explanation, not measured as the cause.

Why researchers looked

Cod liver oil has long been given for bones because of vitamin D; researchers checked whether it protects bones.

Traditional use

Traditionally given to children to prevent rickets and for strong bones.

Proposed mechanism Author hypothesis

The authors suggest vitamin A at past high levels as the reason; not tested directly.

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

This is a safety signal; see the Safety tab. Ask a doctor, especially after the menopause.

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Depression symptoms (survey link)

Very low certainty

In a survey of 21,835 adults in Norway, daily users of cod liver oil had somewhat fewer high depression scores (2.5% versus 3.8%; adjusted OR 0.71). Because it is a snapshot, it cannot show that the oil lowers depression.

1 studiesSelf-reported daily use.

Studies, doses and limits

What the trials found

Hordaland Health Study (Raeder 2007): 8.9% used cod liver oil daily. High depressive symptoms 2.5% in daily users versus 3.8% in others; adjusted OR 0.71 (0.52 to 0.97). Fewer symptoms with longer use in the 40 to 46 age subgroup (P = 0.04 for trend).

Results

A survey link only; no trial of cod liver oil for depression was read.

Effect sizes as reported

Adjusted OR 0.71 (0.52 to 0.97).

Why this rating

Cross-sectional; people who feel well may be more likely to take supplements.

Form and dose studied

Self-reported daily use.

Who was studied

Adults in Norway aged 40 to 49 and 70 to 74.

Limits

Cannot show cause or direction. Not a treatment for depression.

Why researchers looked

Trials suggest omega-3 fats may help depression, so researchers looked at cod liver oil users.

Traditional use

Not a traditional use.

Proposed mechanism Not studied

Not tested.

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

None reported.

¹⁴

Gestational diabetes: blood sugar and inflammation markers

Low certainty

In one Chinese trial of 550 women with gestational diabetes, cod liver oil did not change the main blood-sugar and blood-fat measures after 4 weeks. At 12 to 16 weeks, several secondary measures were lower, including HbA1c, glucose and hs-CRP, and pregnancy complications were less common. The vitamin A in cod liver oil is a concern in pregnancy.

2 studiesCod liver oil with measured EPA and DHA versus mineral oil.

Studies, doses and limits

What the trials found

Yang 2019: 550 women randomised double-blind to cod liver oil or mineral oil. Primary outcomes (HbA1c, fasting glucose, 2-hour glucose, HOMA-IR, lipids at 4 weeks) were not significantly different. Secondary outcomes (HbA1c, glucose, triglycerides, cholesterol, LDL ratio, HOMA-IR, hs-CRP; complications) were lower in the cod liver oil group at 12 to 16 weeks.

Results

Primary results were null; benefits are from secondary outcomes in one trial.

Effect sizes as reported

Primary outcomes P > 0.05; secondary outcomes P < 0.05; no sizes in the abstract.

Why this rating

A single trial with a null primary result and no effect sizes in the abstract.

Form and dose studied

Cod liver oil with measured EPA and DHA versus mineral oil.

Who was studied

Pregnant women with gestational diabetes in China.

Limits

Secondary-outcome findings can be chance. The NHS advises avoiding fish liver oil in pregnancy because of vitamin A.

Why researchers looked

Gestational diabetes carries risks for mother and baby, so researchers look at omega-3 effects on blood sugar.

Traditional use

Not a traditional use.

Proposed mechanism Not studied

Not described in the abstract.

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

Pregnant women should ask a doctor before any supplement; see the Safety tab.

^{21 23}

Heart and circulation (evidence is from omega-3 capsule trials)

Mixed findings

Large reviews of omega-3 supplements, mostly fish oil capsules, found little or no effect on deaths or heart and circulation events, and a small possible fall in coronary heart disease events. Cod liver oil has not been tested on its own in these reviews. High-dose marine omega-3 has also been linked to more atrial fibrillation (an irregular heartbeat).

3 studiesMostly omega-3 capsules.

Studies, doses and limits

What the trials found

Cochrane 2020: 86 trials, 162,796 people. All-cause deaths RR 0.97 (0.93 to 1.01) and cardiovascular events RR 0.96 (0.92 to 1.01), both high-certainty little or no effect. Coronary heart disease events RR 0.91 (0.85 to 0.97), low certainty. Atrial fibrillation meta-analysis 2021: 7 trials, 81,210 people, HR 1.25 (1.07 to 1.46), larger above 1 g a day (HR 1.49). Cod liver oil gives different amounts of EPA and DHA than concentrated capsules and has its own vitamin A and D content. A UK cross-sectional study found cod liver oil users reported fewer cardiovascular conditions, but users were also healthier in other ways.

Results

Mixed: little or no effect on major events; a possible small effect on coronary events; a possible rise in atrial fibrillation.

Effect sizes as reported

See the numbers above.

Why this rating

The evidence is for EPA and DHA supplements in general, not cod liver oil.

Form and dose studied

Mostly omega-3 capsules.

Who was studied

Adults, many with heart disease or risk factors.

Limits

Cod liver oil was not analysed separately.

Why researchers looked

Omega-3 fats from fish are often promoted for the heart.

Traditional use

Oily fish and fish oils have long been linked with heart health.

Proposed mechanism Not studied

Not tested here.

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

Atrial fibrillation risk was higher with more omega-3 per day. Ask a doctor if you have a heart rhythm problem.

^{1 6 10}

Connections to the rest of health

How Cod liver oil 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
Balanced Nutrition	High certainty	A source of vitamin A, vitamin D, EPA and DHA: Cod liver oil is an oil from fish liver that supplies the omega-3 fats EPA and DHA together with vitamins A and D. The USDA lists one tablespoon at about 4,080 micrograms of vitamin A, 34 micrograms of vitamin D, 0.94 g of EPA and 1.49 g of DHA. NCCIH says the vitamin amounts vary from product to product. In a UK cohort, cod liver oil nutrients about doubled people's median intakes.	^{26 22 11 23 13}
Immune Support	Evidence against	Colds, flu-like illness and covid-19 in winter: The largest trial (34,601 adults in Norway) found that cod liver oil in winter did not lower the risk of a positive SARS-CoV-2 test, serious covid-19, or other acute respiratory infections compared with placebo. A smaller 2004 study in young children in New York reported fewer visits for upper respiratory problems with cod liver oil plus a multivitamin, but only two sites were compared and the oil was not tested alone.	^{2 12}
Joint Health	Low certainty	Rheumatoid arthritis: needing less pain medicine: In a 9-month trial of 97 people with rheumatoid arthritis, more people on cod liver oil than on placebo were able to cut their daily NSAID painkiller use by more than 30% (39% versus 10%). Disease activity itself did not differ. Many people dropped out, and this is one small trial. Osteoarthritis pain: A small 1992 trial of 86 people with osteoarthritis who were already taking NSAIDs found no significant benefit from adding cod liver oil compared with olive oil over 24 weeks.	^{5 16}
Pain Relief	Low certainty	Rheumatoid arthritis: needing less pain medicine: In a 9-month trial of 97 people with rheumatoid arthritis, more people on cod liver oil than on placebo were able to cut their daily NSAID painkiller use by more than 30% (39% versus 10%). Disease activity itself did not differ. Many people dropped out, and this is one small trial.	⁵
Pregnancy Health	Mixed findings	Pregnancy and children's thinking skills: In a Norwegian trial, children of mothers who took cod liver oil from pregnancy week 18 to 3 months after birth scored a little higher on a mental processing test at age 4 than children of mothers given corn oil. At age 7 there was no significant difference. Vitamin A is a concern in pregnancy, so health agencies say to avoid cod liver oil supplements then. Gestational diabetes: blood sugar and inflammation markers: In one Chinese trial of 550 women with gestational diabetes, cod liver oil did not change the main blood-sugar and blood-fat measures after 4 weeks. At 12 to 16 weeks, several secondary measures were lower, including HbA1c, glucose and hs-CRP, and pregnancy complications were less common. The vitamin A in cod liver oil is a concern in pregnancy.	^{7 8 22 23 21}
Brain Health	Mixed findings	Pregnancy and children's thinking skills: In a Norwegian trial, children of mothers who took cod liver oil from pregnancy week 18 to 3 months after birth scored a little higher on a mental processing test at age 4 than children of mothers given corn oil. At age 7 there was no significant difference. Vitamin A is a concern in pregnancy, so health agencies say to avoid cod liver oil supplements then.	^{7 8 22 23}
Blood Sugar	Very low certainty	Type 1 diabetes in children (early-life use): Two Norwegian case-control studies found that cod liver oil use was linked to lower odds of childhood type 1 diabetes, but they disagree on when: the 2000 study found a link with the mother's use in pregnancy, and the 2003 study found it with the child's use in the first year but not the mother's use. This is observational and cannot show that the oil prevents diabetes.	^{18 17}
Immune Support	Very low certainty	Multiple sclerosis risk (use in the teen years): In a Norwegian case-control study of 953 people with multiple sclerosis (MS) and 1,717 controls, those who remembered taking cod liver oil at ages 13 to 18 had lower odds of MS (OR 0.67). Use in childhood showed no link. It is observational and based on memory.	³
Bone Health	Very low certainty	Bone density (a possible harm from childhood use): In 3,052 Norwegian women aged 50 to 70, those who recalled taking cod liver oil as children had lower forearm bone density than those who did not. The authors suggest the very high vitamin A content of older products. A 2014 review of prospective studies also links high vitamin A intake to more hip fractures.	^{4 20 24}
Mood	Very low certainty	Depression symptoms (survey link): In a survey of 21,835 adults in Norway, daily users of cod liver oil had somewhat fewer high depression scores (2.5% versus 3.8%; adjusted OR 0.71). Because it is a snapshot, it cannot show that the oil lowers depression.	¹⁴
Blood Sugar	Low certainty	Gestational diabetes: blood sugar and inflammation markers: In one Chinese trial of 550 women with gestational diabetes, cod liver oil did not change the main blood-sugar and blood-fat measures after 4 weeks. At 12 to 16 weeks, several secondary measures were lower, including HbA1c, glucose and hs-CRP, and pregnancy complications were less common. The vitamin A in cod liver oil is a concern in pregnancy.	^{21 23}
Heart Health	Mixed findings	Heart and circulation (evidence is from omega-3 capsule trials): Large reviews of omega-3 supplements, mostly fish oil capsules, found little or no effect on deaths or heart and circulation events, and a small possible fall in coronary heart disease events. Cod liver oil has not been tested on its own in these reviews. High-dose marine omega-3 has also been linked to more atrial fibrillation (an irregular heartbeat).	^{1 6 10}

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Whole Body	Biological association	High certainty	Studied for: A source of vitamin A, vitamin D, EPA and DHA	^{26 22 11 23 13}
Immune System	Biological association	Evidence against	Studied for: Colds, flu-like illness and covid-19 in winter Studied for: Rheumatoid arthritis: needing less pain medicine	^{2 12 5 18 17 3}
Respiratory System	Biological association	Evidence against	Studied for: Colds, flu-like illness and covid-19 in winter	^{2 12}
Musculoskeletal System	Biological association	Low certainty	Studied for: Rheumatoid arthritis: needing less pain medicine Studied for: Osteoarthritis pain	^{5 16 4 20 24}
Nervous System	Biological association	Mixed findings	Studied for: Pregnancy and children's thinking skills Studied for: Multiple sclerosis risk (use in the teen years)	^{7 8 22 23 3 14}
Reproductive System	Biological association	Mixed findings	Studied for: Pregnancy and children's thinking skills Studied for: Gestational diabetes: blood sugar and inflammation markers	^{7 8 22 23 21}
Endocrine System	Biological association	Very low certainty	Studied for: Type 1 diabetes in children (early-life use) Studied for: Gestational diabetes: blood sugar and inflammation markers	^{18 17 21 23}
Cardiovascular System	Biological association	Mixed findings	Studied for: Heart and circulation (evidence is from omega-3 capsule trials)	^{1 6 10}

E. Health conditions

Connected to	Kind of connection	Evidence status	Context	Studies
Atrial fibrillation	Adverse effect or risk	Meta analysis	Higher risk in trials, larger above 1 g a day of omega-3. Marine omega-3 supplements were linked to more atrial fibrillation, mostly at higher amounts. Preparation or compound: Marine omega-3 supplements	⁶
Bone fracture and low bone density	Adverse effect or risk	Observational	High vitamin A intake raised hip fracture risk in cohorts. Preparation or compound: Vitamin A from supplements	^{20 4 24}
Rheumatoid arthritis		Preliminary	One trial found more people could cut NSAID use; disease activity did not change. Preparation or compound: Cod liver oil	⁵

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
Painkiller (NSAID) use in rheumatoid arthritis	Biological association	Low certainty	Measured in trials: lower need (one trial). A lab change is not the same as a health benefit.	⁵
Positive SARS-CoV-2 test	Biological association	High certainty	Measured in trials: no change. A lab change is not the same as a health benefit.	²
Acute respiratory infection (self-reported)	Biological association	High certainty	Measured in trials: no change. A lab change is not the same as a health benefit.	²
Child mental processing score (Kaufman test)	Biological association	Low certainty	Measured in trials: higher at 4 years, not at 7 years. A lab change is not the same as a health benefit.	^{7 8}
Forearm bone mineral density	Biological association	Very low certainty	Measured in trials: lower in users (observational). A lab change is not the same as a health benefit.	⁴
HbA1c in gestational diabetes	Biological association	Low certainty	Measured in trials: lower as a secondary outcome only. A lab change is not the same as a health benefit.	²¹
hs-CRP (inflammation marker)	Biological association	Low certainty	Measured in trials: lower as a secondary outcome. A lab change is not the same as a health benefit.	²¹
Depression symptom score (HADS)	Biological association	Very low certainty	Measured in trials: lower in users (survey). A lab change is not the same as a health benefit.	¹⁴

K. Biological pathways

Connected to	Kind of connection	Evidence status	Context	Studies
Vitamin A	Preliminary mechanism	Human	Supplied in large amounts; limits safe use.	^{24 26}
Vitamin D	Preliminary mechanism	Human	Supplied; excess raises blood calcium.	^{25 26}

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
Retinol (vitamin A)	Biological association	Human	Needed by the body; excess over years linked to bone fragility and, in pregnancy, birth defects. Preparation or compound: Fish liver	^{26 24 15}
Vitamin D (D2 plus D3 as listed by USDA)	Biological association	Human	Needed for calcium balance; excess raises blood calcium. Preparation or compound: Fish liver	^{26 25}
EPA and DHA (long-chain omega-3 fatty acids)	Biological association	Human	Tested in many trials as fish oil; effects on hearts and mood are mixed. Preparation or compound: Fish liver oil	^{26 7 1}

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 the research found for 11 outcomes

1High certainty

2Low certainty

4Very low certainty

2Mixed findings

2Evidence against

Each outcome below is one thing researchers measured. Certainty is how far the evidence can be trusted, not how well it works. The full studies are on the next tab.

A source of vitamin A, vitamin D, EPA and DHA 5 studies High certainty Colds, flu-like illness and covid-19 in winter 2 studies Evidence against Rheumatoid arthritis: needing less pain medicine 1 study Low certainty Osteoarthritis pain 1 study Evidence against Pregnancy and children's thinking skills 4 studies Mixed findings Type 1 diabetes in children (early-life use) 2 studies Very low certainty Multiple sclerosis risk (use in the teen years) 1 study Very low certainty Bone density (a possible harm from childhood use) 3 studies Very low certainty Depression symptoms (survey link) 1 study Very low certainty Gestational diabetes: blood sugar and inflammation markers 2 studies Low certainty Heart and circulation (evidence is from omega-3 capsule trials) 3 studies Mixed findings

The evidence

The research centre for Cod liver oil. Every record here was checked against PubMed or the publisher's page; we never list a study we have not verified.

Evidence by outcome

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 the NHS pages on fish and shellfish, vitamin A and vitamin D and the NCCIH omega-3 page, re-checked nutrient values in saved USDA FoodData Central data, and re-read PubMed abstracts for trials, cohorts and reviews. Only abstracts were read for studies. The NIH Office of Dietary Supplements fact sheets were blocked and are marked unread.

Study library: every study we checked 26

Design Research type Year from Search

Study	Design	People	Product, dose, length	Result
Abdelhamid 2020 Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease. Cochrane Database Syst Rev · PMID 32114706 · DOI	Systematic review meta analysis	162796 86 randomised trials of at least 12 months in adults, mostly in high-income countries; mostly omega-3 capsules	Long-chain omega-3 (EPA and DHA) supplements or advice, mostly fish oil capsules (not cod liver oil specifically) Omega-3 supplements (mainly capsules) From 0.5 g to more than 5 g of long-chain omega-3 a day across trials 12 to 88 months · vs Placebo or usual intake	Little or no effect of more long-chain omega-3 on all-cause deaths or on heart and circulation events (high certainty), and on stroke and arrhythmia. A small fall in coronary heart disease events and deaths was seen (low certainty), with a small fall in cardiovascular deaths (moderate certainty). All-cause deaths RR 0.97; cardiovascular events RR 0.96; coronary heart disease events RR 0.91; cardiovascular deaths RR 0.92 (All-cause 0.93 to 1.01; events 0.92 to 1.01; coronary heart disease events 0.85 to 0.97; cardiovascular deaths 0.86 to 0.99) Methods, limits and funding Outcomes: Deaths, heart and circulation events, blood fats Limitations: About a third of trials were at low risk of bias. Cod liver oil was not separately studied. Funding and conflicts: Not stated in the abstract (Cochrane review). Read: abstract
Brunvoll 2022 Prevention of covid-19 and other acute respiratory infections with cod liver oil supplementation, a low dose vitamin D supplement: quadruple blinded, randomised placebo controlled trial. BMJ · PMID 36215222 · DOI	Randomised controlled trial	34601 Adults aged 18 to 75 in Norway who were not taking daily vitamin D supplements; November 2020 to June 2021	Cod liver oil (provides vitamin D, about 10 micrograms per daily amount) Liquid cod liver oil 5 mL a day (10 micrograms vitamin D) Up to 6 months (median 164 days) · vs Placebo oil	Cod liver oil did not reduce any of the four main outcomes. Positive SARS-CoV-2 test: 227 (1.31%) with cod liver oil versus 228 (1.32%) with placebo. Serious covid-19: 121 (0.70%) versus 101 (0.58%). At least one acute respiratory infection reported: 22.94% versus 22.13%. Only low-grade side effects were reported in either group. Positive SARS-CoV-2 test RR 1.00; serious covid-19 RR 1.20; reported respiratory infection RR 1.04 (Positive test RR 1.00 (adjusted CI 0.82 to 1.22); serious covid-19 1.20 (0.87 to 1.65); reported infections 1.04 (0.97 to 1.11)) Methods, limits and funding Outcomes: Positive SARS-CoV-2 test; serious covid-19; other acute respiratory infections; side effects Limitations: Done in winter in Norway, mostly self-reported symptoms, with a low vitamin D amount. It does not test other doses or people who are deficient. Funding and conflicts: Supported by Orkla Health AS, Oslo University Hospital and the University of Oslo; some authors report grants or fees from companies in the fish-oil field (Olympic Seafood) not related to this paper. Read: abstract
Cortese 2015 Timing of use of cod liver oil, a vitamin D source, and multiple sclerosis risk: The EnvIMS study. Mult Scler · PMID 25948625 · DOI	Case control study	2670 Norway (EnvIMS study): 953 people with multiple sclerosis and 1,717 controls who recalled cod liver oil use from childhood to adulthood	Cod liver oil (self-reported use at different ages) Liquid cod liver oil Estimated vitamin D3 intake by questionnaire Childhood, ages 13 to 18, and adulthood · vs Non-use in the same period	Use at ages 13 to 18 was linked to lower risk of MS (OR 0.67); use in childhood was not (OR 1.01). The link grew with the estimated amount taken in adolescence. Ages 13 to 18: OR 0.67; childhood: OR 1.01 (Ages 13 to 18: 95% CI 0.52 to 0.86; childhood: 0.81 to 1.26) Methods, limits and funding Outcomes: Risk of multiple sclerosis Limitations: Observational and based on memory of use many years ago. It cannot show cause. Funding and conflicts: Some authors report speaker fees or grants from drug companies (listed in the full record); no cod liver oil funding is mentioned in what was read. Read: abstract
Forsmo 2008 Childhood cod liver oil consumption and bone mineral density in a population-based cohort of peri- and postmenopausal women: the Nord-Trondelag Health Study. Am J Epidemiol · PMID 18033763 · DOI	Cohort cross sectional	3052 Women aged 50 to 70 in the Nord-Trøndelag Health Study, Norway, with forearm bone density measured in 2001	Childhood cod liver oil intake (recalled), which at that time was rich in vitamin A Liquid cod liver oil Not measured exactly: recalled use Childhood, measured in adulthood · vs No childhood intake	Women who reported no childhood cod liver oil had higher bone density than those who reported any. The odds of low bone density were 2.3 times higher in women who reported cod liver oil all year round. The authors suggest the past high vitamin A content as a possible reason, noting the vitamin A content had since been cut by 75% in Norway. OR for low bone density 2.3 (95% CI 1.4 to 3.9) Methods, limits and funding Outcomes: Forearm bone mineral density Limitations: Observational and recalled decades later; vitamin A is a possible explanation but was not measured. Today's products may differ. Funding and conflicts: Not stated in the abstract. Read: abstract
Galarraga 2008 Cod liver oil (n-3 fatty acids) as an non-steroidal anti-inflammatory drug sparing agent in rheumatoid arthritis. Rheumatology (Oxford) · PMID 18362100 · DOI	Randomised controlled trial	97 People with rheumatoid arthritis taking NSAID pain medicines; two centres in the UK	Cod liver oil (2.2 g of omega-3 fatty acids) versus air-filled placebo capsules Liquid cod liver oil 10 g a day of cod liver oil 9 months · vs Placebo capsules	19 of 49 (39%) on cod liver oil and 5 of 48 (10%) on placebo cut their NSAID need by more than 30%. No difference between groups in clinical measures of arthritis activity or in side effects. Only 58 of 97 (60%) finished the study. Reduced NSAID use: 39% versus 10% (P = 0.002 (chi-squared); no confidence interval given in the abstract) Methods, limits and funding Outcomes: Share of people able to cut their daily NSAID use by more than 30%; disease activity; side effects Limitations: Small trial; 40% dropped out; the main result is about needing less medicine, not about disease activity, which did not differ. Funding and conflicts: Not stated in the abstract. Read: abstract
Gencer 2021 Effect of Long-Term Marine ɷ-3 Fatty Acids Supplementation on the Risk of Atrial Fibrillation in Randomized Controlled Trials of Cardiovascular Outcomes: A Systematic Review and Meta-Analysis. Circulation · PMID 34612056 · DOI	Systematic review meta analysis	81210 7 large randomised trials of marine omega-3 (81,210 people, mean age 65, mean follow-up 4.9 years)	Marine omega-3 fatty acid supplements (EPA and DHA); not cod liver oil specifically Omega-3 supplements (mainly capsules) Up to 1 g a day or more than 1 g a day across trials Average 4.9 years · vs Placebo	Marine omega-3 supplements were linked to more atrial fibrillation (HR 1.25). The increase was larger in trials testing more than 1 g a day (HR 1.49) than at 1 g or less a day (HR 1.12). HR 1.25 overall; 1.49 above 1 g a day; 1.12 at 1 g or less (Overall 1.07 to 1.46; above 1 g: 1.04 to 2.15; 1 g or less: 1.03 to 1.22) Methods, limits and funding Outcomes: Atrial fibrillation (irregular heartbeat) Limitations: Only 7 trials. Cod liver oil gives a different, usually smaller, amount of EPA and DHA than concentrated capsules, and was not analysed separately. Funding and conflicts: Not stated in the abstract. Read: abstract
Helland 2003 Maternal supplementation with very-long-chain n-3 fatty acids during pregnancy and lactation augments children's IQ at 4 years of age. Pediatrics · PMID 12509593 · DOI	Randomised controlled trial	590 Norwegian women recruited in week 18 of pregnancy (590 recruited, 341 took part until birth); 84 children tested at age 4	Cod liver oil (about 1,183 mg DHA and 803 mg EPA per 10 mL; the same amounts of vitamins A and D were in both oils) versus corn oil Liquid cod liver oil 10 mL a day From week 18 of pregnancy to 3 months after birth · vs Corn oil	Children whose mothers took cod liver oil (n=48) scored higher on the Mental Processing Composite at age 4 than children whose mothers took corn oil (n=36): 106.4 versus 102.3. Mean score 106.4 (SD 7.4) versus 102.3 (SD 11.3) (Not given in the abstract) Methods, limits and funding Outcomes: Child mental processing at age 4 (Kaufman test) Limitations: Many families dropped out (84 of 590 recruited were tested). The comparison oil was corn oil, which is rich in omega-6, not a neutral placebo. Funding and conflicts: One author is affiliated with a company (Möller, Orkla) according to the abstract. Funding is not otherwise stated. Read: abstract
Helland 2008 Effect of supplementing pregnant and lactating mothers with n-3 very-long-chain fatty acids on children's IQ and body mass index at 7 years of age. Pediatrics · PMID 18676533 · DOI	Randomised controlled trial	143 Children tested at age 7 whose mothers had taken cod liver oil or corn oil from week 18 of pregnancy to 3 months after birth	Cod liver oil versus corn oil (maternal) Liquid cod liver oil 10 mL a day Pregnancy week 18 to 3 months after birth · vs Corn oil	There was no significant difference in the Kaufman test at age 7 between children whose mothers took cod liver oil (n=82) and corn oil (n=61). Maternal blood DHA and alpha-linolenic acid during pregnancy were linked to sequential processing scores. No effect on BMI. No significant difference in global IQ (Not given in the abstract) Methods, limits and funding Outcomes: Child IQ (Kaufman test) and body mass index at age 7 Limitations: Follow-up of the same trial; the 4-year benefit did not persist. Funding and conflicts: Not stated in the abstract. Read: abstract
Javaid 2024 Bleeding Risk in Patients Receiving Omega-3 Polyunsaturated Fatty Acids: A Systematic Review and Meta-Analysis of Randomized Clinical Trials. J Am Heart Assoc · PMID 38742535 · DOI	Systematic review meta analysis	120643 11 randomised trials of omega-3 fatty acids (120,643 people)	Omega-3 fatty acids, including high-dose purified EPA (not cod liver oil specifically) Omega-3 supplements (mainly capsules) · vs Control group	Overall there was no increase in bleeding with omega-3 fatty acids (rate ratio 1.09, not significant). In trials of high-dose purified EPA, bleeding risk was about 50% higher in relative terms, a modest absolute rise (0.6%). Background antiplatelet medicine did not change the result. Overall RR 1.09; high-dose purified EPA: about 50% relative increase, 0.6% absolute (Overall 0.91 to 1.31) Methods, limits and funding Outcomes: Bleeding events Limitations: Study-level meta-analysis. Cod liver oil was not separately studied. Funding and conflicts: Not stated in the abstract. Read: abstract
Lentjes 2014 Cod liver oil supplement consumption and health: cross-sectional results from the EPIC-Norfolk cohort study. Nutrients · PMID 25325252 · DOI	Cross sectional study	25639 EPIC-Norfolk cohort, UK, ages 40 to 79; 7-day diet diaries	Cod liver oil as a supplement (self-reported in diaries) Liquid cod liver oil Cross-sectional · vs Other supplement users and non-users	Cod liver oil was the most common supplement. Users were more often women, non-smokers, more active, and had better eating habits. Cod liver oil use was linked with fewer cardiovascular conditions but the authors warn about confounding by indication and healthy-user effects. Descriptive (Not given in the abstract) Methods, limits and funding Outcomes: Who takes cod liver oil and how it relates to health conditions Limitations: Cross-sectional; healthier lifestyle in users makes any link hard to read. Funding and conflicts: Not stated in the abstract. Read: abstract
Lentjes 2015 Contribution of cod liver oil-related nutrients (vitamins A, D, E and eicosapentaenoic acid and docosahexaenoic acid) to daily nutrient intake and their associations with plasma concentrations in the EPIC-Norfolk cohort. J Hum Nutr Diet · PMID 25228113 · DOI	Cohort analysis	6656 EPIC-Norfolk cohort, UK, ages 39 to 79; 7-day diet diaries and blood samples	Cod liver oil-related nutrients (vitamins A, D, E, EPA and DHA) from food and supplements Liquid cod liver oil 7-day diary · vs People not taking the supplement	Cod liver oil nutrients were supplemented by 15% to 33% of people and roughly doubled median intakes. Almost everyone using a vitamin A supplement reached the average requirement, but guideline levels were likely to be exceeded. Blood levels of vitamins A and D tracked intake only weakly; EPA plus DHA tracked more clearly. Supplement use about doubled median intake of these nutrients (Not given in the abstract) Methods, limits and funding Outcomes: Contribution of cod liver oil nutrients to total intake and links with blood levels Limitations: Diary-based; correlations with blood levels were low for vitamins A and D. Funding and conflicts: Not stated in the abstract. Read: abstract
Linday 2004 Effect of daily cod liver oil and a multivitamin-mineral supplement with selenium on upper respiratory tract pediatric visits by young, inner-city, Latino children: randomized pediatric sites. Ann Otol Rhinol Laryngol · PMID 15562899 · DOI	Cluster randomised trial	94 Children aged 6 months to 5 years at two paediatric offices in upper Manhattan (one site given supplements, one used as a records control)	Lemon-flavoured cod liver oil plus a children's multivitamin-mineral supplement with selenium (combined, so the effect cannot be assigned to the oil alone) Liquid cod liver oil One teaspoon a day for children aged 1 or over (half to start for under 1) About 5 to 6 months, winter to spring · vs Medical records of a control site	Visits for upper respiratory problems fell over time at the supplement site (P = 0.042) and did not change at the control site. About 70% of children completed the course. Fewer visits over time at the supplement site (Not given in the abstract) Methods, limits and funding Outcomes: Number of upper respiratory tract paediatric visits Limitations: Only two sites were randomised, so site differences could explain the result. Cod liver oil was given together with a multivitamin. Not placebo-controlled. Funding and conflicts: Not stated in the abstract. Read: abstract
Linday 2010 Cod liver oil, young children, and upper respiratory tract infections. J Am Coll Nutr · PMID 21677119 · DOI	Narrative article	Article by the author of two small trials of cod liver oil in young children	Cod liver oil (with a children's multivitamin/mineral supplement with selenium in the author's own studies) Liquid cod liver oil Winter and early spring in the author's cluster-randomised study	Says cod liver oil was a traditional source of vitamin D in the United States and was used to prevent and treat rickets, and that it is culturally valued as a folk remedy by many low-income families. Reports that in the author's cluster-randomised study these supplements cut paediatric visits for upper respiratory illness by 36% to 58%. Visits per child per month fell 36% to 58% in the author's study (Not given in the abstract) Methods, limits and funding Outcomes: Background on traditional use; upper respiratory visits in the author's own work Limitations: An opinion-style article by the trial author, partly arguing for insurance coverage. It is not an independent review. Funding and conflicts: Not stated in the abstract. Read: abstract
Raeder 2007 Associations between cod liver oil use and symptoms of depression: the Hordaland Health Study. J Affect Disord · PMID 17184843 · DOI	Cross sectional study	21835 Hordaland Health Study, Norway: adults aged 40 to 49 and 70 to 74, questionnaires	Daily cod liver oil use (self-reported) Liquid cod liver oil Not measured exactly Cross-sectional (one point in time) · vs Non-users	Daily users of cod liver oil were less likely to have high depression symptom scores: 2.5% versus 3.8% (adjusted OR 0.71). Symptoms were also lower with longer use, in the 40 to 46 age subgroup. Adjusted OR 0.71 (95% CI 0.52 to 0.97) Methods, limits and funding Outcomes: High symptom scores for depression and anxiety (HADS scale) Limitations: Cross-sectional: it cannot say whether the oil lowers depression or people with fewer symptoms are more likely to take it. Funding and conflicts: Not stated in the abstract. Read: abstract
Rothman 1995 Teratogenicity of high vitamin A intake. N Engl J Med · PMID 7477116 · DOI	Cohort study	22748 22,748 pregnant women in the United States, interviewed about diet and supplements in the first trimester	Preformed vitamin A (retinol) from food and supplements (not cod liver oil specifically) Vitamin A in food and supplements Above 10,000 IU a day from supplements, or above 15,000 IU from food and supplements, compared with 5,000 IU or less First trimester · vs Mothers with 5,000 IU or less a day	High intake of preformed vitamin A was linked to more birth defects of cranial neural crest tissue: ratio 3.5 for more than 15,000 IU a day from food and supplements, and 4.8 for more than 10,000 IU a day from supplements alone. An apparent threshold was near 10,000 IU a day of supplemental vitamin A, concentrated before the seventh week. The authors estimated about 1 infant in 57 had a malformation attributable to the supplement above 10,000 IU. Prevalence ratio 3.5 (food and supplements above 15,000 IU); 4.8 (supplements above 10,000 IU) (3.5: 95% CI 1.7 to 7.3; 4.8: 95% CI 2.2 to 10.5) Methods, limits and funding Outcomes: Birth defects, especially those of cranial neural crest tissue Limitations: Observational (1995). Diet was recalled by the mother. Cod liver oil was not analysed on its own. Funding and conflicts: Not stated in the abstract. Read: abstract
Stammers 1992 Efficacy of cod liver oil as an adjunct to non-steroidal anti-inflammatory drug treatment in the management of osteoarthritis in general practice. Ann Rheum Dis · PMID 1540019 · DOI	Randomised controlled trial	86 People with osteoarthritis taking NSAIDs, seen in general practice in London	Cod liver oil added to usual NSAID treatment Liquid cod liver oil 10 mL a day 24 weeks · vs Olive oil	There was no significant benefit for people taking cod liver oil compared with olive oil. No significant difference (Not given in the abstract) Methods, limits and funding Outcomes: Joint pain and inflammation; interference with daily activities; unwanted effects Limitations: A short report from 1992 with a small group; no numbers are given in the abstract. Funding and conflicts: Not stated in the abstract. Read: abstract
Stene 2000 Use of cod liver oil during pregnancy associated with lower risk of Type I diabetes in the offspring. Diabetologia · PMID 11043854 · DOI	Case control study	1156 Vest-Agder county, Norway: 85 children with diabetes and 1,071 controls; mailed questionnaire	Cod liver oil taken by the mother during pregnancy Liquid cod liver oil Not measured exactly: questionnaire During pregnancy · vs Non-users	Mothers who took cod liver oil in pregnancy had children with a lower risk (unadjusted OR 0.30, still significant after adjusting). Multivitamins in pregnancy, cod liver oil in the first year of life (adjusted OR 0.82) and other vitamin D supplements in the first year were not significantly linked. Unadjusted odds ratio 0.30 (95% CI 0.12 to 0.75) Methods, limits and funding Outcomes: Risk of type 1 diabetes in the child Limitations: Small number of cases (85). Observational and self-reported. The larger 2003 national study did not find the pregnancy link, so the two disagree. Funding and conflicts: Not stated in the abstract. Read: abstract
Stene 2003 Use of cod liver oil during the first year of life is associated with lower risk of childhood-onset type 1 diabetes: a large, population-based, case-control study. Am J Clin Nutr · PMID 14668274 · DOI	Case control study	2213 Norwegian children: 545 with childhood-onset type 1 diabetes and 1,668 population controls, questionnaires about early supplement use	Cod liver oil (self-reported use in the first year of life or by mothers in pregnancy) Liquid cod liver oil Not measured exactly: frequency of use by questionnaire First year of life or pregnancy · vs Non-users	Use of cod liver oil in the first year of life was linked to a lower risk of type 1 diabetes (adjusted OR 0.74). Other vitamin D supplements in the first year, and maternal use of cod liver oil or other vitamin D supplements in pregnancy, were not linked to the risk. Adjusted odds ratio 0.74 (95% CI 0.56 to 0.99) Methods, limits and funding Outcomes: Risk of childhood-onset type 1 diabetes Limitations: Observational: it cannot show cause. Use was self-reported afterwards. Families who gave cod liver oil may differ in other ways. Funding and conflicts: Not stated in the abstract. Read: abstract
Storelli 2004 Polychlorinated biphenyls, hexachlorobenzene, hexachlorocyclohexane isomers, and pesticide organochlorine residues in cod-liver oil dietary supplements. J Food Prot · PMID 15330552 · DOI	Laboratory analysis n/a	Cod liver oil dietary supplements sold in Italy, analysed in a laboratory	Cod liver oil supplements (PCBs, DDTs and other organochlorine residues measured) Cod liver oil supplements · vs WHO tolerable range for dioxin-like compounds	Total PCBs ranged from 25 to 201 ng per gram of fat and DDTs from 25 to 133 ng per gram. At manufacturers' suggested amounts, estimated daily intake of dioxin-like PCBs was below the WHO range of 1 to 4 pg per kg body weight per day (0.74 pg at most). The authors call for strict continuing monitoring. Intake of dioxin-like PCBs up to 0.74 pg TEQ per kg per day (Not applicable) Methods, limits and funding Outcomes: Contaminant levels and estimated daily intake Limitations: Old (2004) analysis of products from one country; today's products may differ. Funding and conflicts: Not stated in the abstract. Read: abstract
Wu 2014 The relationship between vitamin A and risk of fracture: meta-analysis of prospective studies. J Bone Miner Res · PMID 24700407 · DOI	Meta-analysis	283930 Prospective studies: 8 intake studies (283,930 people) and 4 blood retinol studies (8,725 people)	Vitamin A, retinol and beta-carotene intake and blood retinol (not cod liver oil specifically) Dietary and supplement vitamin A Prospective follow-up · vs Lower intake	High intake of vitamin A and of retinol raised the risk of hip fracture. Beta-carotene did not. Both high and low blood retinol were linked to higher hip-fracture risk (a U-shaped pattern). Total fracture risk did not differ significantly. Hip fracture: vitamin A RR 1.29; retinol RR 1.40; high blood retinol RR 1.87; low blood retinol RR 1.56 (Vitamin A 1.07 to 1.57; retinol 1.03 to 1.91; high blood retinol 1.31 to 2.65; low 1.09 to 2.22) Methods, limits and funding Outcomes: Hip fracture and total fracture Limitations: Observational cohorts, so not proof of cause. Cod liver oil was not analysed on its own. Funding and conflicts: Not stated in the abstract. Read: abstract
Yang 2019 Cod-Liver Oil Improves Metabolic Indices and hs-CRP Levels in Gestational Diabetes Mellitus Patients: A Double-Blind Randomized Controlled Trial. J Diabetes Res · PMID 31956660 · DOI	Randomised controlled trial	550 550 women with gestational diabetes in China	Cod liver oil (EPA 76 mg/mL and DHA 150 mg/mL, measured by gas chromatography) versus mineral oil Liquid cod liver oil Amount per day not given in the abstract 12 to 16 weeks, middle to late pregnancy · vs Mineral oil placebo	After the first 4 weeks there was no significant difference in the primary outcomes (HbA1c, glucose, insulin resistance, blood fats). For the secondary outcomes at 12 to 16 weeks, HbA1c, glucose, triglycerides, cholesterol, LDL ratio, HOMA-IR and hs-CRP were lower with cod liver oil, and pregnancy complications were less frequent. Primary outcomes: no significant difference (P > 0.05). Secondary outcomes: lower with cod liver oil (P < 0.05). (Not given in the abstract) Methods, limits and funding Outcomes: Blood sugar (HbA1c, fasting and 2-hour glucose), insulin resistance, blood fats, hs-CRP, pregnancy complications Limitations: Primary outcomes were null; benefits come from secondary outcomes, which carry a higher chance of a false finding. The abstract does not give amounts or effect sizes. One trial from one team. Funding and conflicts: Authors declare no conflict of interest. Read: abstract
s-nccih-omega3 NCCIH: Omega-3 Supplements: What You Need To Know (last updated November 2024) · Source	Regulator page n/a			Methods, limits and funding Read: full-text
s-nhs-fish Fish and shellfish: nutrition (NHS; page last reviewed 26 June 2026) · Source	Regulator page n/a			Methods, limits and funding Read: full-text
s-nhs-vitamin-a Vitamin A (NHS; page last reviewed 3 August 2020, next review was due 3 August 2023) · Source	Regulator page n/a			Methods, limits and funding Read: full-text
s-nhs-vitamin-d Vitamin D (NHS; page last reviewed 3 August 2020) · Source	Regulator page n/a			Methods, limits and funding Read: full-text
s-usda-sr-legacy-cod-liver-oil USDA FoodData Central, SR Legacy (April 2018 release): "Fish oil, cod liver" (FDC 173577) · Source	Reference database n/a			Methods, limits and funding Read: full-text

What we do not know yet

No cod liver oil trial for heart disease; heart results come from omega-3 capsule trials.
The official US upper intake limits (NIH Office of Dietary Supplements) could not be read.
No trial tested cod liver oil for type 1 diabetes, multiple sclerosis, bone health or depression.
Oxidation and label accuracy of cod liver oil products were not researched.
Whether cod liver oil can trigger fish-allergy reactions was not found in a source read.
Cod liver oil was not compared with fish oil capsules in a trial.

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 8

●

Painkiller (NSAID) use in rheumatoid arthritis

Lower need (one trial) in trials

How much anti-inflammatory painkiller a person needs each day.

Low certainty

Results and what it means

Why it was measured

To see whether cod liver oil lets people take less medicine.

Statistical vs. clinical meaning

A small trial; disease activity did not change.

Safety implication

Medicine changes need a doctor.

Study	Result	People	Product
⁵	39% versus 10% reduced NSAID need by more than 30% (P = 0.002)	97 people with RA	Cod liver oil (2.2 g n-3 fatty acids in 10 g) for 9 months

⁵

●

Positive SARS-CoV-2 test

No change in trials

A positive PCR test for the virus that causes covid-19.

High certainty

Results and what it means

Why it was measured

To see whether cod liver oil prevents infection.

Statistical vs. clinical meaning

No effect. A single large trial, so rated as strong evidence of no effect.

Safety implication

Only low-grade side effects were reported.

Study	Result	People	Product
²	227 (1.31%) versus 228 (1.32%); RR 1.00 (adjusted CI 0.82 to 1.22)	34,601 adults in Norway	5 mL a day cod liver oil versus placebo, median 164 days

●

Acute respiratory infection (self-reported)

No change in trials

Any cold-like or other acute respiratory infection that people reported.

High certainty

Results and what it means

Why it was measured

To see whether cod liver oil reduces colds and similar illness.

Statistical vs. clinical meaning

No protective effect in adults; self-reported symptoms.

Safety implication

None reported.

Study	Result	People	Product
²	22.94% versus 22.13%; RR 1.04 (0.97 to 1.11)	34,601 adults in Norway	Cod liver oil versus placebo in winter

●

Child mental processing score (Kaufman test)

Higher at 4 years, not at 7 years in trials

A test of children's thinking and problem solving.

Low certainty

Results and what it means

Why it was measured

To see whether mothers' cod liver oil in pregnancy affects the child's development.

Statistical vs. clinical meaning

A small early difference that was not seen at 7 years.

Safety implication

Vitamin A in pregnancy: see the Safety tab.

Study	Result	People	Product
⁷	106.4 versus 102.3 at age 4	84 children at 4 years	Maternal cod liver oil or corn oil from week 18 of pregnancy to 3 months after birth
⁸	No significant difference at age 7	143 children at 7 years	Same maternal supplementation

^{7 8}

●

Forearm bone mineral density

Lower in users (observational) in trials

How dense the bone is in the forearm, a marker of bone strength.

Very low certainty

Results and what it means

Why it was measured

To see whether childhood cod liver oil protects or harms bones.

Statistical vs. clinical meaning

Observational; possible vitamin A explanation.

Safety implication

Possible harm signal.

Study	Result	People	Product
⁴	OR for low bone density 2.3 (1.4 to 3.9) with year-round childhood use	3,052 women aged 50 to 70	Recalled childhood cod liver oil

⁴

●

HbA1c in gestational diabetes

Lower as a secondary outcome only in trials

A blood measure of average blood sugar over weeks.

Low certainty

Results and what it means

Why it was measured

To see whether cod liver oil lowers blood sugar in gestational diabetes.

Statistical vs. clinical meaning

Primary outcome null; secondary outcome only.

Safety implication

Pregnancy: see the Safety tab.

Study	Result	People	Product
²¹	No significant difference for the primary outcome at 4 weeks; lower in the cod liver oil group at 12 to 16 weeks (P < 0.05)	550 women with gestational diabetes	Cod liver oil versus mineral oil

²¹

●

hs-CRP (inflammation marker)

Lower as a secondary outcome in trials

A blood test that rises with inflammation.

Low certainty

Results and what it means

Why it was measured

To see whether cod liver oil lowers inflammation.

Statistical vs. clinical meaning

A marker, not a health outcome.

Safety implication

None reported.

Study	Result	People	Product
²¹	Lower with cod liver oil at 12 to 16 weeks (P < 0.05)	550 women with gestational diabetes	Cod liver oil versus mineral oil

²¹

●

Depression symptom score (HADS)

Lower in users (survey) in trials

A questionnaire that scores symptoms of depression and anxiety.

Very low certainty

Results and what it means

Why it was measured

To compare symptoms in cod liver oil users and non-users.

Statistical vs. clinical meaning

Cross-sectional only.

Safety implication

None reported.

Study	Result	People	Product
¹⁴	High scores in 2.5% of daily users versus 3.8% of others; adjusted OR 0.71 (0.52 to 0.97)	21,835 adults in Norway	Daily cod liver oil by self-report

¹⁴

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 4

Cod liver oil is high in vitamin A, which can harm an unborn baby. The NHS says fish liver oil supplements are high in vitamin A, and that anyone who is pregnant should avoid supplements containing vitamin A, including fish liver oil such as cod liver oil. It also advises avoiding them when trying for a baby unless a GP says otherwise. A large US cohort of 22,748 pregnant women found more birth defects of the head and face (cranial neural crest) with high intakes of preformed vitamin A, with an apparent threshold near 10,000 IU a day from supplements. Authoritative guidance and cohort study ^{23 15}
Too much vitamin A over years may weaken bones. The NHS says that taking more than an average of 1.5 mg (1,500 micrograms) of vitamin A a day from food and supplements for many years may make bones more likely to fracture, especially in older people and women after the menopause. A meta-analysis found high vitamin A and retinol intake raised the risk of hip fracture. By the USDA entry, one tablespoon of cod liver oil has about 4,080 micrograms of vitamin A, so the amount in a product matters a great deal; products differ. Authoritative guidance and meta analysis ^{24 20 26 4}
Too much vitamin D raises blood calcium. The NHS says too much vitamin D over a long time can build up calcium in the body (hypercalcaemia), which can weaken bones and damage the kidneys and the heart. Cod liver oil adds to vitamin D from other supplements, so the total counts. Authoritative guidance ^{25 26}
Added together, nutrients from the oil can pass guideline levels. In the UK EPIC-Norfolk cohort, cod liver oil nutrients about doubled median intakes of vitamins A, D and E and of EPA and DHA, and guideline levels for vitamin A were likely to be exceeded in people taking a vitamin A supplement. NCCIH says the vitamin A and D amounts vary from product to product. Cohort analysis and authoritative guidance ^{11 22}

Side effects 4

Effect	How often	Severity and recovery	Evidence
Unpleasant taste, bad breath, bad-smelling sweat, headache, heartburn, nausea, diarrhoea These are described for omega-3 supplements in general.	NCCIH says omega-3 side effects are usually mild; the 34,601-person winter trial reported only low-grade side effects in both the cod liver oil and placebo groups.	Usually mild Not stated in the sources read.	Authoritative guidance and randomised trial ^{22 2}
Atrial fibrillation (irregular heartbeat) The trials used marine omega-3 capsules and concentrates; cod liver oil was not analysed on its own.	A meta-analysis of 7 trials (81,210 people) found marine omega-3 supplements linked to more atrial fibrillation: HR 1.25 (1.07 to 1.46), larger above 1 g a day of omega-3 (HR 1.49).	Can be serious Not stated in the abstract.	Meta analysis of trials ⁶
Bleeding Cod liver oil was not separately studied. Ask a doctor or pharmacist before use with blood-thinning medicines.	A 2024 meta-analysis of 11 trials (120,643 people) found no overall increase in bleeding with omega-3 (rate ratio 1.09, 0.91 to 1.31). Trials of high-dose purified EPA showed about a 50% higher relative risk of bleeding, a 0.6% absolute rise.	Modest Not stated in the abstract.	Meta analysis of trials ⁹
Vitamin A excess: bone fragility and, in pregnancy, birth defects Related to the amount of vitamin A in a product.	See the key safety points and the pregnancy section.	Can be serious Not stated in the sources read.	Authoritative guidance, cohort study and meta analysis ^{24 15 20}

Liver

No source read described liver injury from cod liver oil, and the liver-safety database LiverTox was not opened. Vitamin A can build up in the liver, but no source read described this for cod liver oil.

How often. No frequency was found.

Monitoring. No agency monitoring advice was found.

This is a safety connection. It is not evidence that Cod liver oil supports liver health.

Medicines and supplements 5

With	Why it matters	Importance	Evidence	What to do
Other sources of vitamin A (liver, liver pâté, multivitamins, other fish liver oils) supplement	Vitamin A from several sources adds up.	The NHS says people who eat liver once a week should not take vitamin A supplements, including fish liver oil, and that total vitamin A should stay at or under 1.5 mg a day on average.	Regulator High certainty ^{24 23}	Check labels of multivitamins; ask a pharmacist.
Other vitamin D supplements supplement	Vitamin D from several products adds up.	The NHS says not to take more than 100 micrograms (4,000 IU) of vitamin D a day for adults, because of hypercalcaemia.	Regulator High certainty ²⁵	Add up the vitamin D from all products; ask a pharmacist.
Blood-thinning and antiplatelet medicines prescription	Omega-3 fats may affect blood clotting.	A 2024 meta-analysis found no overall rise in bleeding with omega-3, and background antiplatelet use did not change the result; high-dose purified EPA showed a modest rise.	Trials Low certainty ⁹	Ask a doctor or pharmacist.
Retinoid medicines (such as those for acne or psoriasis) prescription	Retinoids are related to vitamin A, so taking extra vitamin A could add to their effects.	No source read for this page described this interaction, so it is not confirmed here.	Not checked Not enough evidence	Ask a pharmacist before combining.
Heart rhythm medicines and heart rhythm problems condition	Marine omega-3 supplements were linked to more atrial fibrillation in trials.	HR 1.25 overall; larger above 1 g a day of omega-3.	Meta-analysis Moderate certainty ⁶	Ask a doctor if you have a heart rhythm problem.

Who should check first 6

Situation	Advice	Evidence
Pregnancy and trying for a baby	The NHS says to avoid supplements containing vitamin A, including fish liver oil such as cod liver oil, in pregnancy, and unless a GP advises otherwise when trying for a baby, because too much vitamin A can harm an unborn baby. The Norwegian pregnancy trials gave cod liver oil, but the NHS advice is to avoid it. Ask a doctor or midwife.	Authoritative guidance and cohort ^{23 15 7}
Breastfeeding	No source read gave cod liver oil advice for breastfeeding other than the trial in Norway, which continued to 3 months after birth. Ask a doctor, midwife or pharmacist. The LactMed database was not opened.	Not established ⁷
Women after the menopause and older men	The NHS says these groups, who are more at risk of osteoporosis, should avoid more than 1.5 mg of vitamin A a day from food and supplements combined, including fish liver oil. A Norwegian study linked childhood cod liver oil to lower bone density in later life.	Authoritative guidance and observational ^{24 4}
Children and babies	The NHS gives lower upper limits of vitamin D for babies and younger children than for adults; cod liver oil products differ in strength. Give children supplements only on the advice of a doctor, health visitor or pharmacist.	Authoritative guidance ^{25 22}
Fish allergy	The NHS says fish and shellfish allergies are quite common and can be severe, and that people allergic to one type of fish often react to others. No source read said whether cod liver oil can trigger a reaction, so ask a doctor or allergist before using it.	Authoritative guidance (general fish allergy) ²³
Kidney disease, high blood calcium, heart rhythm problems or bleeding disorders	Too much vitamin D raises blood calcium and can damage kidneys and heart (NHS). Marine omega-3 was linked to more atrial fibrillation in trials. No source read gave cod liver oil advice for kidney disease or bleeding disorders. Ask a doctor first.	Authoritative guidance and meta analysis ^{25 6 9}

Overdose, product quality and regulators

Summary. Cod liver oil is an oil, but its vitamin A and D content is what limits safe use over time. The harm comes from long-term excess, not from a single use.

Animal. Not reviewed.

High dose or long term signals. NHS: long-term vitamin A above 1.5 mg a day on average may weaken bones; vitamin D above 100 micrograms a day may cause hypercalcaemia. A US pregnancy cohort linked high preformed vitamin A to birth defects.

Overdose response. No source read described what happens with a single large swallow of cod liver oil. If someone has swallowed a lot, call poison control or emergency services.

Genotoxicity. Not researched.

Fish oils can carry traces of environmental pollutants, and the vitamin content of cod liver oil products varies.

Pollutants (PCBs and pesticides). A 2004 laboratory analysis of cod liver oil supplements sold in Italy found PCBs from 25 to 201 ng per gram of fat and DDTs from 25 to 133 ng per gram. Estimated daily intake of dioxin-like PCBs at the makers' suggested amounts was at most 0.74 pg TEQ per kg body weight, below the WHO range of 1 to 4 pg. The authors still call for strict monitoring. Products today may differ. ¹⁹

Vitamin content varies. NCCIH says the vitamin A and D in cod liver oil vary from product to product, so the label matters. In Norway, the vitamin A content of commercial cod liver oil was cut by 75% around the time of one study. ^{22 4}

Body	Action	Date
NHS (UK) (United Kingdom)	Fish and shellfish page: fish liver oil supplements are high in vitamin A; do not have more than 1.5 mg a day from food and supplements combined; in pregnancy avoid supplements containing vitamin A, including fish liver oil such as cod liver oil; avoid them when trying for a baby unless a GP advises otherwise. Vitamin A page: more than 1.5 mg a day over many years may affect bones; people who eat liver weekly should not take vitamin A supplements including fish liver oil. Vitamin D page: do not take more than 100 micrograms (4,000 IU) of vitamin D a day for adults and children aged 11 to 17. source	2026-06-26
NCCIH (US National Institutes of Health) (United States)	Fish liver oil supplements such as cod liver oil contain EPA and DHA plus vitamins A and D in amounts that vary by product; vitamins A and D can be harmful in excess. Omega-3 side effects are usually mild. source	2024-11

When to get medical help

Someone has swallowed a large amount of cod liver oil, or vitamin A or D products: call poison control or emergency services.
Wheezing, swelling of the lips or face, hives or trouble breathing after using it (possible allergy): get emergency help.
A new fast, uneven or fluttering heartbeat, chest pain or fainting: get medical help.
Constant thirst, passing a lot of urine, nausea, vomiting or confusion after long use of vitamin D products (possible high blood calcium): see a doctor.
Pregnant or trying for a baby and taking cod liver oil or other vitamin A products: stop and talk to a doctor or midwife.
Unusual bleeding or bruising, or black stools, if you also take blood thinners: see a doctor.

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 is cod liver oil?

Cod liver oil is an oil taken from the liver of cod and related fish. It supplies the omega-3 fats EPA and DHA and, unlike ordinary fish oil, large amounts of vitamins A and D. The amounts differ by product.

^{22 26}

How is cod liver oil different from fish oil?

Fish oil usually comes from the flesh of oily fish and gives EPA and DHA. Cod liver oil comes from the liver and also carries a lot of vitamin A and vitamin D. That is why it has extra cautions. Fish oil has its own page here.

^{22 23}

Does cod liver oil prevent colds or covid-19?

In a trial of 34,601 adults in Norway, cod liver oil in winter did not lower the risk of covid-19 or other respiratory infections compared with placebo. A small children's study gave a different signal but was weaker.

^{2 12}

Does cod liver oil help arthritis?

One 9-month trial found more people with rheumatoid arthritis could cut their NSAID painkillers (39% versus 10%), but arthritis activity did not change. A small older trial found no benefit for osteoarthritis. Do not change medicines without a doctor.

^{5 16}

Is cod liver oil safe in pregnancy?

The NHS says to avoid it in pregnancy and, unless a GP advises otherwise, when trying for a baby, because its vitamin A can harm an unborn baby. Ask a doctor or midwife about omega-3 options.

^{23 15}

Can cod liver oil weaken bones?

Too much vitamin A over many years may. The NHS says more than 1.5 mg a day on average, from food and supplements, may make bones more likely to fracture, and a Norwegian study linked childhood cod liver oil to lower bone density. Products differ, so read labels.

^{24 4 20}

Can you get too much vitamin D from it?

Yes. Too much vitamin D over a long time can raise blood calcium and harm the kidneys and heart, says the NHS. Cod liver oil adds to vitamin D from other supplements, so the total counts.

²⁵

Does cod liver oil help the heart?

Large reviews of omega-3 capsules found little or no effect on deaths or heart events, and a small possible fall in coronary events. Cod liver oil itself was not studied on its own. High amounts of marine omega-3 were linked to more atrial fibrillation.

^{1 6}

What are the side effects?

NCCIH says omega-3 side effects are usually mild: bad taste, bad breath, headache, heartburn, nausea and diarrhoea. Vitamin A and D excess are the more serious risks over time.

^{22 2}

Does it interact with medicines?

Vitamin A and D from several products add up. A 2024 review found no overall extra bleeding with omega-3, but high-dose purified EPA showed a modest rise. Ask a pharmacist if you take blood thinners or retinoid medicines; retinoid interactions were not confirmed in a source read.

^{24 9}

Is there contamination in cod liver oil?

A 2004 analysis of supplements sold in Italy found traces of PCBs and pesticide residues, with estimated intakes below the WHO range for dioxin-like compounds. Products today may differ.

¹⁹

Does it help type 1 diabetes or multiple sclerosis?

Observational studies in Norway found links with lower odds, but they rely on memory, and the two diabetes studies disagree on timing. No trial shows cod liver oil prevents either condition.

^{18 17 3}

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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 the NHS pages on fish and shellfish, vitamin A and vitamin D and the NCCIH omega-3 page, re-checked nutrient values in saved USDA FoodData Central data, and re-read PubMed abstracts for trials, cohorts and reviews. Only abstracts were read for studies. The NIH Office of Dietary Supplements fact sheets were blocked and are marked unread.
How we rate evidence: See "How we rate evidence" in the Evidence tab.
Independence: No product is promoted on this page. No affiliate links are shown. Trials of cod liver oil products may have manufacturer links not stated in abstracts.

Sources 26

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

Abdelhamid AS, Brown TJ, Brainard JS, Biswas P, Thorpe GC, Moore HJ et al.. Omega-3 fatty acids for the primary and secondary prevention of cardiovascular disease.. Cochrane Database Syst Rev. 2020. PMID 32114706. DOI 10.1002/14651858.CD003177.pub5. (abstract)
Brunvoll SH, Nygaard AB, Ellingjord-Dale M, Holland P, Istre MS, Kalleberg KT et al.. Prevention of covid-19 and other acute respiratory infections with cod liver oil supplementation, a low dose vitamin D supplement: quadruple blinded, randomised placebo controlled trial.. BMJ. 2022. PMID 36215222. DOI 10.1136/bmj-2022-071245. (abstract)
Cortese M, Riise T, Bjørnevik K, Holmøy T, Kampman MT, Magalhaes S et al.. Timing of use of cod liver oil, a vitamin D source, and multiple sclerosis risk: The EnvIMS study.. Mult Scler. 2015. PMID 25948625. DOI 10.1177/1352458515578770. (abstract)
Forsmo S, Fjeldbo SK, Langhammer A. Childhood cod liver oil consumption and bone mineral density in a population-based cohort of peri- and postmenopausal women: the Nord-Trondelag Health Study.. Am J Epidemiol. 2008. PMID 18033763. DOI 10.1093/aje/kwm320. (abstract)
Galarraga B, Ho M, Youssef HM, Hill A, McMahon H, Hall C et al.. Cod liver oil (n-3 fatty acids) as an non-steroidal anti-inflammatory drug sparing agent in rheumatoid arthritis.. Rheumatology (Oxford). 2008. PMID 18362100. DOI 10.1093/rheumatology/ken024. (abstract)
Gencer B, Djousse L, Al-Ramady OT, Cook NR, Manson JE, Albert CM. Effect of Long-Term Marine ɷ-3 Fatty Acids Supplementation on the Risk of Atrial Fibrillation in Randomized Controlled Trials of Cardiovascular Outcomes: A Systematic Review and Meta-Analysis.. Circulation. 2021. PMID 34612056. DOI 10.1161/CIRCULATIONAHA.121.055654. (abstract)
Helland IB, Smith L, Saarem K, Saugstad OD, Drevon CA. Maternal supplementation with very-long-chain n-3 fatty acids during pregnancy and lactation augments children's IQ at 4 years of age.. Pediatrics. 2003. PMID 12509593. DOI 10.1542/peds.111.1.e39. (abstract)
Helland IB, Smith L, Blomén B, Saarem K, Saugstad OD, Drevon CA. Effect of supplementing pregnant and lactating mothers with n-3 very-long-chain fatty acids on children's IQ and body mass index at 7 years of age.. Pediatrics. 2008. PMID 18676533. DOI 10.1542/peds.2007-2762. (abstract)
Javaid M, Kadhim K, Bawamia B, Cartlidge T, Farag M, Alkhalil M. Bleeding Risk in Patients Receiving Omega-3 Polyunsaturated Fatty Acids: A Systematic Review and Meta-Analysis of Randomized Clinical Trials.. J Am Heart Assoc. 2024. PMID 38742535. DOI 10.1161/JAHA.123.032390. (abstract)
Lentjes MA, Welch AA, Mulligan AA, Luben RN, Wareham NJ, Khaw KT. Cod liver oil supplement consumption and health: cross-sectional results from the EPIC-Norfolk cohort study.. Nutrients. 2014. PMID 25325252. DOI 10.3390/nu6104320. (abstract)
Lentjes MA, Mulligan AA, Welch AA, Bhaniani A, Luben RN, Khaw KT. Contribution of cod liver oil-related nutrients (vitamins A, D, E and eicosapentaenoic acid and docosahexaenoic acid) to daily nutrient intake and their associations with plasma concentrations in the EPIC-Norfolk cohort.. J Hum Nutr Diet. 2015. PMID 25228113. DOI 10.1111/jhn.12271. (abstract)
Linday LA, Shindledecker RD, Tapia-Mendoza J, Dolitsky JN. Effect of daily cod liver oil and a multivitamin-mineral supplement with selenium on upper respiratory tract pediatric visits by young, inner-city, Latino children: randomized pediatric sites.. Ann Otol Rhinol Laryngol. 2004. PMID 15562899. DOI 10.1177/000348940411301108. (abstract)
Linday LA. Cod liver oil, young children, and upper respiratory tract infections.. J Am Coll Nutr. 2010. PMID 21677119. DOI 10.1080/07315724.2010.10719894. (abstract)
Raeder MB, Steen VM, Vollset SE, Bjelland I. Associations between cod liver oil use and symptoms of depression: the Hordaland Health Study.. J Affect Disord. 2007. PMID 17184843. DOI 10.1016/j.jad.2006.11.006. (abstract)
Rothman KJ, Moore LL, Singer MR, Nguyen US, Mannino S, Milunsky A. Teratogenicity of high vitamin A intake.. N Engl J Med. 1995. PMID 7477116. DOI 10.1056/NEJM199511233332101. (abstract)
Stammers T, Sibbald B, Freeling P. Efficacy of cod liver oil as an adjunct to non-steroidal anti-inflammatory drug treatment in the management of osteoarthritis in general practice.. Ann Rheum Dis. 1992. PMID 1540019. DOI 10.1136/ard.51.1.128. (abstract)
Stene LC, Ulriksen J, Magnus P, Joner G. Use of cod liver oil during pregnancy associated with lower risk of Type I diabetes in the offspring.. Diabetologia. 2000. PMID 11043854. DOI 10.1007/s001250051499. (abstract)
Stene LC, Joner G, Norwegian Childhood Diabetes Study Group. Use of cod liver oil during the first year of life is associated with lower risk of childhood-onset type 1 diabetes: a large, population-based, case-control study.. Am J Clin Nutr. 2003. PMID 14668274. DOI 10.1093/ajcn/78.6.1128. (abstract)
Storelli MM, Storelli A, Marcotrigiano GO. Polychlorinated biphenyls, hexachlorobenzene, hexachlorocyclohexane isomers, and pesticide organochlorine residues in cod-liver oil dietary supplements.. J Food Prot. 2004. PMID 15330552. DOI 10.4315/0362-028x-67.8.1787. (abstract)
Wu AM, Huang CQ, Lin ZK, Tian NF, Ni WF, Wang XY et al.. The relationship between vitamin A and risk of fracture: meta-analysis of prospective studies.. J Bone Miner Res. 2014. PMID 24700407. DOI 10.1002/jbmr.2237. (abstract)
Yang S, Lin R, Si L, Li Z, Jian W, Yu Q et al.. Cod-Liver Oil Improves Metabolic Indices and hs-CRP Levels in Gestational Diabetes Mellitus Patients: A Double-Blind Randomized Controlled Trial.. J Diabetes Res. 2019. PMID 31956660. DOI 10.1155/2019/7074042. (abstract)
. NCCIH: Omega-3 Supplements: What You Need To Know (last updated November 2024). . . (full-text)
. Fish and shellfish: nutrition (NHS; page last reviewed 26 June 2026). . . (full-text)
. Vitamin A (NHS; page last reviewed 3 August 2020, next review was due 3 August 2023). . . (full-text)
. Vitamin D (NHS; page last reviewed 3 August 2020). . . (full-text)
. USDA FoodData Central, SR Legacy (April 2018 release): "Fish oil, cod liver" (FDC 173577). . . (full-text)

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
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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.