Black tea: the brewed drink and the dried leaf.

Black Tea

Q: Is black tea the same as a tea extract or supplement?

No. A cup of tea is a weak water extract. Extracts, powders and capsules are concentrated products. Liver warnings exist for green tea catechin extracts (EFSA); nothing equivalent was read for black tea extract, so the page makes no claim about it. Do not carry results from one product to the other.

Q: Does black tea lower cholesterol?

Maybe slightly, but reviews disagree. A pooled analysis of 10 trials found LDL cholesterol 4.64 mg/dL lower and Cochrane found a fall in black tea trials. A review in people with high cholesterol and a review of 14 short trials found no significant effect.

Q: Does black tea lower blood pressure?

Small falls have been reported. Cochrane found about 1.85 mmHg lower systolic pressure with black tea. A review of green or black tea found larger falls with green stronger than black, and a review of 14 short trials found none. Do not use tea in place of blood pressure treatment.

Q: Do people who drink black tea live longer or have fewer heart problems?

In 38 cohort data sets, the highest tea intake was linked with about 10% lower all-cause and 14% lower heart-disease death. This is an association; tea types were not separated and cause is uncertain. No trial of black tea has measured heart attacks, strokes or deaths.

Q: Does black tea help with diabetes or blood sugar?

Not clearly. Ten trials of tea or tea extract in people with type 2 diabetes found no significant change in fasting blood sugar. A cohort meta-analysis found no clear overall link with developing diabetes. Talk to your doctor before changing diabetes care.

Q: Does black tea help focus, memory or mood?

Not shown for the drink itself. A review of 50 trials found small gains mainly for L-theanine plus caffeine as isolated compounds, mostly in short tests. The reviewers ask for more trials using actual tea.

Q: Does black tea have caffeine, and can it affect sleep?

Yes. A lab study found 14 to 61 mg per serving in white, green and black teas, and the FDA lists 71 mg in a 12 fl oz cup. Caffeine can cause jitters and fast heartbeat, and EFSA says it may affect sleep in some adults, especially near bedtime. Sensitivity varies and some medicines raise it.

Q: Does tea affect iron?

It can. Black tea reduced iron absorption from a test meal by 79 to 94%, and the NHS tells people with iron deficiency anaemia to eat and drink less tea. A French study of healthy adults found no link between tea drinking and iron stores.

Q: Is black tea safe in pregnancy, breastfeeding or for children?

It counts toward your caffeine limit. The NHS says no more than 200 mg of caffeine a day in pregnancy and counts about 75 mg in a cup of tea, and EFSA says up to 200 mg a day does not raise concerns for the foetus. The FDA suggests asking a health care provider about caffeine while breastfeeding and quotes guidance to avoid caffeinated drinks for children under 2. Ask a clinician.

Camellia sinensis · also called Black tea, tea (fully oxidised tea leaf). Not the same as a tea extract or supplement.

Black tea is a drink made from the leaves of the tea plant, fully oxidised (often called fermented) before drying. People drink it for alertness, heart health and general wellbeing. Pooled trials show small and mixed effects on cholesterol and blood pressure, and studies that follow people over time link tea with lower death rates but cannot prove cause. The main cautions are its caffeine, its effect on iron absorption, and very hot drinks.

General information, not medical advice. Last substantive update October 25, 2026 · Not medically reviewed. A named clinician has not signed off on this page. How this page is made

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About Black Tea

Black tea is the drink from fully oxidised tea leaves. Research gives small and mixed results for cholesterol and blood pressure and no clear effect on blood sugar in trials. Large studies link tea drinking with lower death rates, but cannot show cause. The drink has caffeine, can lower iron absorption, and very hot tea is a risk for the oesophagus. Extracts and capsules are a separate product.

What it is

Black tea comes from the leaves of Camellia sinensis, a plant of the tea family (Theaceae) that GBIF accepts as a species. Green, black, oolong and white tea all come from this one plant and differ in how the leaves are processed. Black tea is the fully oxidised kind. Herbal teas such as peppermint or chamomile come from other plants.

The drink contains caffeine, theaflavins and other oxidation products of tea polyphenols, and a little L-theanine. One black tea trial reported theaflavins at 90 mg per litre of tea, but amounts vary a lot between products.

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Tea, extract or supplement?

A cup of black tea is a weak water extract of the leaf. Extracts, powders and capsules are concentrated products, and results from one do not carry over to the other. The liver warnings that exist for tea extracts come from green tea: EFSA noted rare liver injury after green tea infusions and raised liver enzymes with high-dose catechin supplements, and a review of 159 human studies tied liver effects to concentrated, catechin-rich preparations rather than brewed tea. No safety study of black tea extract was found in the sources read, so the page makes no claim about it.

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What the research shows

Cholesterol: reviews disagree. One pooled analysis of 10 trials and the Cochrane review found falls in LDL; a review in people with high cholesterol and a review of 14 short trials did not. Blood pressure: small falls in some reviews, none in the review of short trials, and black tea looked weaker than green.

In large groups followed over time, the highest tea intake was linked with lower all-cause and heart-disease death. The authors and a later review say this does not prove cause. Trials of tea or extract in type 2 diabetes found no clear effect on blood sugar, and one single trial in healthy adults reported large falls in glucose and fats that has not been repeated.

For focus and mood, a review of 50 trials found its clearest effects for theanine plus caffeine, not tea itself.

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Fluoride and metals

Tea plants take up fluoride. A study of 121 black teas found the most fluoride in tea-bag infusions and about twice as much in African teas as in Central or East Asian teas. A second study found all fluoride hazard scores below the threshold, but highest in older low-weight women. A study of 8 brands found metals lower in the infusion than in the dry leaf and within limits, with arsenic worth monitoring. No pesticide figures were read.

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Regulators and status

The FDA, the NHS and EFSA give caffeine guidance that includes tea. IARC classed very hot beverages as probably carcinogenic to the oesophagus. No black tea monograph was opened from the EMA, and NCCIH, LiverTox and Health Canada pages for black tea were not read.

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At a glance

Traditional uses history, not proof

Black tea is one of the most widely drunk teas. EFSA reports that tea was the main source of caffeine in the UK and Ireland.
No traditional-use or history source for black tea was read, so none is claimed here.

Studied for research

Cholesterol (LDL), mixed
Blood pressure, low
Heart disease and death rates in drinkers (an association), low
Risk of type 2 diabetes (an association), low
Blood sugar in type 2 diabetes, low (no clear effect)
Blood sugar and fats in healthy adults (one trial), very low
Focus and mood, insufficient

Main compounds

Caffeine
Theaflavins and other oxidation products (thearubigins)
Polyphenols such as flavan-3-ols and flavonols
L-theanine
Oxalate

Common forms

Brewed loose-leaf or tea-bag tea (the form studied here)
Bottled, sweetened and flavoured teas (different products; not covered by these studies)
Concentrated tea extracts, powders and capsules (a different product; no black tea extract safety study was read)

Research links: FDA: How much caffeine is too much · NHS: Foods to avoid in pregnancy · NHS: Iron deficiency anaemia · EFSA: Caffeine risk assessment explained · Cochrane: green and black tea and heart disease prevention (abstract) · Meta-analysis: black tea and cholesterol (abstract) · Research Library · Genes & Biomarkers Library

What it is and its history

Accepted scientific name: Camellia sinensis
Naming authority: (L.) Kuntze
Synonyms: Camellia thea Link; Camellia bohea (L.) Sweet; Camellia chinensis (Sims) Kuntze; Camellia sinensis var. bohea (L.) Kunzte
Common names: Black tea (English); Tea (English); Té (Spanish); Planta de té (Spanish)
Family or group: Theaceae (the tea family)
Classification: Plantae > Ericales > Theaceae > Camellia > Camellia sinensis
Native range: Not checked in the sources read.
Habitat: Not checked.
What it looks like: Stems: Not checked.; Leaves: The leaf is the part used. For black tea it is fully oxidised before drying (the fermented tea of the reviews read; no botanical source was opened).; Flowers: Not checked.; Fruit: Not checked.
Cultivation: Not checked.
Harvest and processing: A review of oxidised tea polyphenols groups black tea with oolong and dark tea as fermented teas, unlike unfermented green tea. EFSA describes green tea as made without fermentation, which prevents oxidation of the polyphenols. The sources read give no step-by-step process for black tea and none is given here.
Look-alikes and adulterants: Name: Other teas from the same plant; Note: Green, oolong, white and pu-erh tea are the same species processed differently; their research and safety findings do not transfer automatically.; Name: Herbal teas; Note: Peppermint, chamomile and similar drinks are made from other plants and usually have no caffeine; a lab study found no caffeine in the herbal teas it tested.; Name: Tea extracts and supplements; Note: Concentrated products are not the same as a cup of tea.
Sustainability and conservation: Not checked.

Photographs

A clear glass cup of deep amber-red black tea beside a small pile of dried black tea leaves — Black tea: the brewed drink and the dried leaf.

Traditional use and history history, not clinical proof

Tradition or era	Documented use	Source
Not covered	No history source for black tea was read in this round, so no traditional uses are claimed. The only usage fact from the sources read is that tea is a major daily source of caffeine in the UK and Ireland (EFSA).	s-efsa-caffeine

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
Caffeine PubChem 2519	methylxanthine (stimulant)	Leaf A lab study found 14 to 61 mg per serving in white, green and black teas; the FDA lists 71 mg in 12 fl oz of black tea.	Stimulates the central nervous system (EFSA); can raise heart rate and disturb sleep in sensitive people. ^{30 3 27 25}	Human data
Theaflavins PubChem 135403798	polyphenol pigments formed when tea is oxidised	Leaf A Mauritian black tea used in one trial contained theaflavins at 90 mg per litre.	Often named as a possible active in black tea; no human study in the sources read isolates their effect. ^{31 2}	Not established
Theaflavin 3,3'-digallate PubChem 135536164	theaflavin (polyphenol pigment)	Leaf Not read.	Not studied in the sources read. ³²	Not assessed
Thearubigins and other oxidation products	larger oxidation products of tea polyphenols	Leaf Not read.	A review notes that oxidation products of tea polyphenols differ greatly from one tea type to the next. None of the sources read measured thearubigins on their own. ²¹	Not assessed
Gallic acid derivatives, flavan-3-ols and flavonols	polyphenols	Leaf All were measured in the Mauritian tea of one trial (see paper).	Polyphenols in tea bind iron and lower its absorption from a meal. ^{2 9}	Human data
L-Theanine PubChem 439378	amino acid	Leaf Not read for black tea.	With caffeine, linked with small short-term gains in attention and mood in trials of the isolated compounds. ^{33 20}	Human data
Oxalate	organic acid	Leaf (infusion) A kidney-stone trial listed black tea as high in oxalate (86 mg a day in the test phase).	Raises the question of kidney stones; trials and surveys disagree. ²²	Human data

Mechanisms, receptors and pathways

Target or pathway	Gene or receptor	What was found	Level
Central nervous system stimulation by caffeine	n/a	EFSA says caffeine stimulates the central nervous system and in moderate doses increases alertness and reduces sleepiness. ²⁵	Human data
Iron absorption (polyphenol binding)	n/a	In human volunteers, polyphenol drinks reduced iron absorption in a dose-dependent way related to their total polyphenol content; black tea was more inhibitory than cocoa and several herb teas at the same polyphenol amount. ⁹	Human data
Weight and fat metabolism through gut bacteria (hypothesis)	n/a	The authors of one review propose that tea polyphenols block carbohydrate-digesting enzymes and interact with gut bacteria to make short-chain fatty acids that change fat metabolism, and say fermented teas may trigger this more than green tea. It is the authors' own hypothesis and results are inconsistent. ²¹	Hypothesis by reviewers
Heart and blood-vessel effects (suggested)	n/a	Reviewers list plausible antioxidant, anti-inflammatory, blood-vessel, anti-clotting and gut-bacteria effects, but say a causal effect has not been shown. ¹⁵	Hypothesis by reviewers

Absorption, metabolism and elimination

Absorption: EFSA says caffeine taken by mouth is absorbed rapidly and completely.
Distribution: Not covered.
Metabolism: EFSA says the time to remove half of a caffeine dose varies widely with age, body weight, pregnancy, medicines and liver function.
Elimination: The EFSA factsheet gives a range of about two to eight hours for adults.
Bioavailability: Not covered for theaflavins or other tea polyphenols in the sources read.

²⁵

Isolated compounds versus whole extracts

A cup of black tea is a water extract of the oxidised leaf. Isolated caffeine, isolated theanine and concentrated extracts are different products. The thinking and mood review found its clearest effects for theanine with caffeine, not tea drinks; the liver warnings are for green tea catechin extracts, not brewed tea. Do not carry results from one form to another.

Nutritional composition

Black tea is not a source of essential nutrients worth relying on. A study of eight brands found that the essential minerals in an infusion add only a small fraction of daily needs. Tea adds fluid and caffeine, and tea polyphenols can lower iron absorption from a meal.

7benefits and uses looked at

34studies and sources checked

Low certaintybest evidence rating found

7lab markers tracked in trials

1 mixed findings4 low certainty1 very low certainty1 not enough evidence

What was looked at

The 7 benefits and uses checked for Black Tea, each with how strong the evidence is. Tap one to open it.

Cholesterol (LDL)Mixed findings
Blood pressureLow certainty
Heart disease and death rates in tea drinkersLow certainty
Risk of developing type 2 diabetesLow certainty
Blood sugar in people with type 2 diabetesLow certainty
Blood sugar and blood fats in healthy adults (one trial)Very low certainty
Thinking, mood and focusNot enough evidence

Lab markers tracked in the studies

LDL cholesterolTotal cholesterolSystolic blood pressureDiastolic blood pressureFasting blood glucoseFasting insulinTriglycerides

What is Black Tea good for?

The uses people ask about and how strong the human evidence is for each. Many reviews pool green and black tea or all tea types, so none of these results is a clean answer about one cup of black tea.

Cholesterol (LDL)Mixed findingsA pooled analysis of 10 trials found LDL cholesterol about 4.6 mg/dL lower and Cochrane found a fall in black tea trials, but reviews in people with high cholesterol and of short trials found no significant effect. Blood pressureLow certaintyCochrane found a small fall in systolic pressure with black tea, a review of green or black tea found larger falls (green stronger than black), and a review of short trials found none. Observational studies link tea with modestly lower odds of high blood pressure. Heart disease and death rates in tea drinkersLow certaintyIn 38 cohort data sets (nearly 2 million people), the highest tea intake was linked with about 10% lower all-cause and 14% lower heart-disease death. This is an association, and tea types were not separated. Risk of type 2 diabetesLow certaintyA meta-analysis of 19 cohort studies found no clear overall link between tea and type 2 diabetes, with a lower risk only at the highest intake. Observational only. Blood sugar in type 2 diabetesLow certaintyTen trials of tea or tea extract in people with type 2 diabetes found no clear change in fasting blood sugar, with small changes in fasting insulin and waist size. Blood sugar and blood fats in healthy adults (one trial)Very low certaintyOne 12-week trial in healthy adults reported large falls in fasting glucose and triglycerides compared with hot water. It is a single trial, larger than the pooled reviews suggest, and needs repeating. Thinking, mood and focusNot enough evidenceA review of 50 trials found small gains mainly for theanine plus caffeine, not for tea drinks. Whether black tea helps focus is not shown.

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.

Cholesterol (LDL)

Mixed findings

Pooled trials of black tea drinks found a small average fall in LDL cholesterol, but a review in people with high cholesterol and a review of short green or black tea trials found no clear effect.

4 studiesBrewed black tea as a drink. Amounts and tea types differed between t…

Studies, doses and limits

What the trials found

A 2015 meta-analysis of 10 trials (411 people) found LDL lower by 4.64 mg/dL. A Cochrane review of 4 black tea trials found a fall of 0.43 mmol/L over about six months, with few trials and a risk of bias. A 2019 review of 6 trials in people with high cholesterol, and a 2020 review of 14 green or black tea trials, found no significant effect.

Results

Zhao 2015: LDL -4.64 mg/dL (95% CI -8.99 to -0.30); total cholesterol -2.04 and HDL -1.15 not significant. Cochrane 2013 (black tea): LDL MD -0.43 mmol/L (-0.56 to -0.31). Araya-Quintanilla 2019: no significant change in total, LDL, HDL or triglycerides in high-cholesterol adults. Igho-Osagie 2020: no significant change in any blood fat.

Effect sizes as reported

Small average fall in some reviews; none in others. The reviews do not agree.

Why this rating

Four reviews point in different directions. Trials are small and short, the largest fall comes from a handful of trials with a risk of bias, and two reviews found nothing. No heart attack or stroke outcome has been measured.

Form and dose studied

Brewed black tea as a drink. Amounts and tea types differed between trials, and this page gives no amounts. No capsule or extract trials were read.

Who was studied

Healthy adults, adults at higher heart risk, and adults with high cholesterol, mostly in short trials.

Limits

Small trials; tea type and amount differed; one review mixes green and black tea; a lab number is not a heart outcome.

Why researchers looked

High LDL cholesterol is a risk factor for heart disease, and black tea contains polyphenols (theaflavins and thearubigins) that are often suggested to help.

Traditional use

Not described in the sources read.

Proposed mechanism Not established

No mechanism was established in the sources read. Black tea contains theaflavins, thearubigins, catechins and caffeine, but the reviews read do not show which of them, if any, explains these results.

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

Black tea has caffeine, can lower iron absorption and is not a treatment for high cholesterol. See the Safety tab. Ask a doctor about cholesterol treatment.

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Blood pressure

Low certainty

Some pooled trials found small average falls in blood pressure with black or green tea, but a review of short trials found none, and black tea looked weaker than green.

4 studiesBrewed tea as a drink. Amounts differed and are not given here.

Studies, doses and limits

What the trials found

The Cochrane review of black tea trials found systolic pressure 1.85 mmHg lower over about six months. A 2020 review of 5 trials (408 people with raised or high blood pressure) of green or black tea found falls of 4.81 mmHg systolic and 1.98 mmHg diastolic, with green tea stronger than black. A 2020 review of 14 trials found no significant effect. A 2026 review of 20 observational studies links tea drinking with modestly lower odds of high blood pressure, with a stronger link in black tea drinkers that the authors call hypothesis-generating.

Results

Cochrane 2013 (black tea): SBP MD -1.85 mmHg (-3.21 to -0.48); DBP -1.27 (-3.06 to 0.53, not significant). Mahdavi-Roshan 2020 (green or black): SBP WMD -4.81 (-8.40 to -1.58); DBP -1.98 (-3.77 to -0.20). Igho-Osagie 2020: no significant change. Jiang 2026: cross-sectional OR 0.92 (0.87 to 0.97); cohort OR 0.87 (0.84 to 0.92).

Effect sizes as reported

A few mmHg at most in trials that found an effect; no effect in the review of short trials.

Why this rating

Few trials with different results, green and black tea pooled in most of them, and the observational data cannot show cause. The reviewers disagree.

Form and dose studied

Brewed tea as a drink. Amounts differed and are not given here.

Who was studied

Adults with raised or high blood pressure, and healthy adults.

Limits

Five to fourteen small trials per review; short follow-up; observational findings may reflect other habits.

Why researchers looked

High blood pressure is a major risk factor for heart disease and stroke, and tea is an everyday drink that people ask about.

Traditional use

Not described in the sources read.

Proposed mechanism Not established

No mechanism was established in the sources read. Black tea contains theaflavins, thearubigins, catechins and caffeine, but the reviews read do not show which of them, if any, explains these results.

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

Caffeine can raise heart rate and blood pressure briefly in some people. Do not use tea in place of blood pressure treatment.

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Heart disease and death rates in tea drinkers

Low certainty

In large groups followed over time, people who drank the most tea had about 10% lower death from any cause and about 14% lower death from heart disease. This is a link, not proof that tea is the cause.

3 studiesTea as usually drunk. This page gives no amounts to aim for.

Studies, doses and limits

What the trials found

A 2024 meta-analysis pooled 38 cohort data sets (1,956,549 people). The highest tea intake was linked to 0.90 times the all-cause death risk and 0.86 times the heart-disease death risk, with no clear link to cancer death. The biggest gains were around 1.5 to 2 cups a day. A 2026 narrative review says causal inference is uncertain. The Cochrane review found no trial of black tea that reported heart events.

Results

Kim 2024: all-cause ES 0.90 (0.86 to 0.95); CVD death 0.86 (0.79 to 0.94); cancer death 0.90 (0.78 to 1.03, not significant). Liu 2026: evidence does not support picking a tea type for a disease or a standard therapeutic amount. Cochrane 2013: no heart events reported by any trial.

Effect sizes as reported

10% lower all-cause and 14% lower heart-disease death in the highest versus lowest intake groups.

Why this rating

Observational data only. The tea types were not separated, so it is not a black-tea-only result, and people who drink more tea may differ in other ways.

Form and dose studied

Tea as usually drunk. This page gives no amounts to aim for.

Who was studied

Adults in cohort studies worldwide.

Limits

Confounding and reverse cause are possible; tea types and preparation differ; no trial has tested black tea for heart attack, stroke or death.

Why researchers looked

Tea is drunk daily by many people, so even small effects could matter, and population studies can look at heart attacks and death that short trials cannot.

Traditional use

Not described in the sources read.

Proposed mechanism Pharmacological theory

The reviewers describe plausible antioxidant, anti-inflammatory, blood-vessel and gut-bacteria effects, but say a causal effect has not been shown and Mendelian randomisation studies have not consistently supported one.

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

These results do not mean more tea is safer. See the Safety tab for caffeine, iron and very hot drinks.

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Risk of developing type 2 diabetes

Low certainty

Across 19 large follow-up studies there was no clear overall link between tea drinking and type 2 diabetes. A lower risk showed up only in people drinking four or more cups a day. This is an association and tea types were not separated.

1 studiesTea as usually drunk, types not separated. No amounts are recommended…

Studies, doses and limits

What the trials found

A 2023 paper reported a cohort of 5,199 adults in China (relative risk 1.02, no link) and a meta-analysis of 19 cohort studies (1,076,311 people): pooled relative risk 0.96 (0.91 to 1.00), and 0.83 (0.76 to 0.90) for four or more cups a day.

Results

Li 2023: own cohort RR 1.02 (0.82 to 1.28); pooled RR 0.96 (0.91 to 1.00); 4 or more cups a day RR 0.83 (0.76 to 0.90).

Effect sizes as reported

No overall effect; 17% lower risk at the highest intake in a pooled association.

Why this rating

Observational only, tea types not separated, self-reported intake, and the overall result sits on the line of no effect.

Form and dose studied

Tea as usually drunk, types not separated. No amounts are recommended here.

Who was studied

Adults in cohort studies.

Limits

Confounding by other habits is likely; heavy tea drinkers may differ from others; no trial of risk.

Why researchers looked

Tea polyphenols such as theaflavins are suggested to affect how the body handles sugar.

Traditional use

Not described in the sources read.

Proposed mechanism Pharmacological theory

The authors suggest polyphenols such as theaflavins may have a blood-sugar-lowering effect, but their own cohort did not show an effect and no mechanism was established.

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

Very high tea intake means a lot of caffeine and can lower iron absorption. See the Safety tab.

¹⁴

Blood sugar in people with type 2 diabetes

Low certainty

Ten trials of tea or tea extract in people with type 2 diabetes found no clear change in fasting blood sugar. There were small changes in fasting insulin and waist size.

1 studiesTea or tea extract, pooled; this is not a black-tea-drink-only result.

Studies, doses and limits

What the trials found

A 2016 meta-analysis of 10 randomised trials (608 people) of tea or tea extract in type 2 diabetes. It does not separate black tea from other tea or from extracts.

Results

Fasting glucose -0.05 mmol/L (-0.51 to 0.40), not significant; LDL, HDL, triglycerides, blood pressure and insulin resistance not significant; tea reduced the fall in fasting insulin (1.30 U/L) and waist circumference fell 2.70 cm only in trials longer than 8 weeks.

Effect sizes as reported

No clear effect on blood sugar.

Why this rating

Small trials, tea and extract pooled, and not black-tea-specific.

Form and dose studied

Tea or tea extract, pooled; this is not a black-tea-drink-only result.

Who was studied

Adults with type 2 diabetes.

Limits

Small trials; the review pooled several kinds of tea and extract.

Why researchers looked

People with type 2 diabetes look for everyday drinks that might help control blood sugar.

Traditional use

Not described in the sources read.

Proposed mechanism Not established

No mechanism was established in the sources read.

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

Do not change diabetes treatment because of tea. Talk to your doctor.

¹³

Blood sugar and blood fats in healthy adults (one trial)

Very low certainty

One 12-week trial in healthy adults in Mauritius found large falls in fasting glucose and triglycerides with a daily black tea infusion compared with hot water. It is a single trial with some design problems and is far larger than the pooled reviews suggest.

1 studiesA plain black tea infusion without additives. No amounts are recommen…

Studies, doses and limits

What the trials found

One randomised trial (Mauritian black tea, 12 weeks plus a 3-week wash-out, hot water as the control; 71% of people in the tea group and 29% in the control group).

Results

Fasting glucose fell 18.4% (P<0.001) and triglycerides 35.8% (P<0.01); LDL/HDL ratio fell 16.6% (P<0.05); HDL rose 20.3% (not significant); a blood antioxidant measure rose 418%.

Effect sizes as reported

Large percent changes in one trial.

Why this rating

One trial, unequal groups, a hot-water control, no blinding details in the abstract, numbers of people not given, and results far larger than the pooled reviews. It needs to be repeated.

Form and dose studied

A plain black tea infusion without additives. No amounts are recommended here.

Who was studied

Healthy adults in Mauritius.

Limits

Single trial; funding not stated in the abstract; antioxidant blood markers are not health outcomes.

Why researchers looked

The authors wanted to test whether everyday black tea changes heart risk markers in people with normal health.

Traditional use

Not described in the abstract.

Proposed mechanism Human data

Not established. The authors report the tea was rich in theaflavins and other polyphenols and that blood antioxidant levels rose.

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

No safety problems were reported in the abstract. See the Safety tab for caffeine and iron.

Thinking, mood and focus

Not enough evidence

A review of 50 trials found small gains in attention and mood mainly for the compound L-theanine taken together with caffeine, not for tea drinks. Whether a cup of black tea helps focus is not shown.

1 studiesIsolated L-theanine and caffeine, not black tea. No amounts are recom…

Studies, doses and limits

What the trials found

A 2025 meta-analysis of 50 randomised trials in healthy people tested tea, L-theanine, and L-theanine plus caffeine. Most trials used the isolated compounds, not tea drinks.

Results

Theanine plus caffeine versus placebo in the first two hours: for example attention switching accuracy SMD 0.33 (0.13 to 0.54). Theanine alone: choice reaction time SMD -0.35 at hour 1. The reviewers say the intervals often leave the size and direction uncertain and ask for more research using actual tea drinks.

Effect sizes as reported

Small to moderate for theanine with caffeine; unknown for black tea.

Why this rating

The evidence is for isolated compounds, mostly short single-dose tests; very little tested black tea itself.

Form and dose studied

Isolated L-theanine and caffeine, not black tea. No amounts are recommended here.

Who was studied

Healthy adults.

Limits

Short tests, healthy people only, little tea-drink data.

Why researchers looked

Black tea contains caffeine and a smaller amount of L-theanine, and people drink it to feel alert and calm.

Traditional use

Not described in the sources read.

Proposed mechanism Human data

The reviewers point to theanine and caffeine acting together; no mechanism is proven.

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

Caffeine can disturb sleep and raise heart rate. See the Safety tab.

²⁰

Connections to the rest of health

How Black Tea 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	Kind of connection	Evidence status	Context	Studies
Cholesterol Balance		Mixed findings	Cholesterol (LDL): Pooled trials of black tea drinks found a small average fall in LDL cholesterol, but a review in people with high cholesterol and a review of short green or black tea trials found no clear effect.	^{24 7 1 10}
Heart Health		Mixed findings	Cholesterol (LDL): Pooled trials of black tea drinks found a small average fall in LDL cholesterol, but a review in people with high cholesterol and a review of short green or black tea trials found no clear effect. Blood pressure: Some pooled trials found small average falls in blood pressure with black or green tea, but a review of short trials found none, and black tea looked weaker than green.	^{24 7 1 10 16 11}
Blood Pressure Support		Low certainty	Blood pressure: Some pooled trials found small average falls in blood pressure with black or green tea, but a review of short trials found none, and black tea looked weaker than green.	^{7 16 10 11}
Heart Health	Biological association	Low certainty	Heart disease and death rates in tea drinkers: In large groups followed over time, people who drank the most tea had about 10% lower death from any cause and about 14% lower death from heart disease. This is a link, not proof that tea is the cause.	^{12 15 7}
Healthy Aging	Biological association	Low certainty	Heart disease and death rates in tea drinkers: In large groups followed over time, people who drank the most tea had about 10% lower death from any cause and about 14% lower death from heart disease. This is a link, not proof that tea is the cause.	^{12 15 7}
Blood Sugar Balance	Biological association	Low certainty	Risk of developing type 2 diabetes: Across 19 large follow-up studies there was no clear overall link between tea drinking and type 2 diabetes. A lower risk showed up only in people drinking four or more cups a day. This is an association and tea types were not separated.	¹⁴
Blood Sugar Balance		Low certainty	Blood sugar in people with type 2 diabetes: Ten trials of tea or tea extract in people with type 2 diabetes found no clear change in fasting blood sugar. There were small changes in fasting insulin and waist size.	¹³
Blood Sugar Balance		Very low certainty	Blood sugar and blood fats in healthy adults (one trial): One 12-week trial in healthy adults in Mauritius found large falls in fasting glucose and triglycerides with a daily black tea infusion compared with hot water. It is a single trial with some design problems and is far larger than the pooled reviews suggest.	²
Cholesterol Balance		Very low certainty	Blood sugar and blood fats in healthy adults (one trial): One 12-week trial in healthy adults in Mauritius found large falls in fasting glucose and triglycerides with a daily black tea infusion compared with hot water. It is a single trial with some design problems and is far larger than the pooled reviews suggest.	²
Better Focus		Not enough evidence	Thinking, mood and focus: A review of 50 trials found small gains in attention and mood mainly for the compound L-theanine taken together with caffeine, not for tea drinks. Whether a cup of black tea helps focus is not shown.	²⁰
Mental Clarity		Not enough evidence	Thinking, mood and focus: A review of 50 trials found small gains in attention and mood mainly for the compound L-theanine taken together with caffeine, not for tea drinks. Whether a cup of black tea helps focus is not shown.	²⁰

B. Body systems

Connected to	Kind of connection	Evidence status	Context	Studies
Sleep Recovery	Adverse effect or risk	Low certainty	Caffeine may disturb sleep in some adults, especially close to bedtime (EFSA). Preparation or compound: Caffeine in black tea	^{25 27}
Cardiovascular System	Biological association	Mixed findings	Studied for: Cholesterol (LDL) Studied for: Blood pressure	^{24 7 1 10 16 11}
Heart Circulation	Biological association	Low certainty	Studied for: Heart disease and death rates in tea drinkers	^{12 15 7}
Blood Sugar Support	Biological association	Low certainty	Studied for: Risk of developing type 2 diabetes Studied for: Blood sugar in people with type 2 diabetes	^{14 13 2}
Brain Focus	Biological association	Not enough evidence	Studied for: Thinking, mood and focus	²⁰

C. Body parts and organs

Connected to	Kind of connection	Evidence status	Context	Studies
Heart	Adverse effect or risk	Low certainty	Caffeine can speed the heartbeat and cause palpitations in sensitive people (FDA). Preparation or compound: Caffeine in black tea	²⁷

E. Health conditions

Connected to	Kind of connection	Evidence status	Context	Studies
Iron deficiency	Drug or supplement interaction	Moderate certainty	Black tea lowered iron absorption from a test meal; the NHS advises people with iron deficiency anaemia to have less tea; healthy French adults showed no link with iron stores. Preparation or compound: Black tea polyphenols	^{9 28 19}
Kidney stones	Adverse effect or risk	Mixed findings	Studies disagree on tea and calcium-oxalate stones. Preparation or compound: Black tea (oxalate)	^{22 5 23}
Pregnancy	Contraindication	Low certainty	Tea counts toward the daily caffeine limit in pregnancy (NHS; EFSA). Preparation or compound: Caffeine in black tea	^{29 25}

I. Biomarkers

Connected to	Kind of connection	Evidence status	Context	Studies
LDL cholesterol	Biological association	Mixed findings	Measured in trials: lowered in some reviews. A lab change is not the same as a health benefit.	^{24 7 1 10}
Total cholesterol	Biological association	Low certainty	Measured in trials: unchanged. A lab change is not the same as a health benefit.	^{24 1}
Systolic blood pressure	Biological association	Low certainty	Measured in trials: lowered slightly in some reviews. A lab change is not the same as a health benefit.	^{7 16 10}
Diastolic blood pressure	Biological association	Low certainty	Measured in trials: unchanged or lowered slightly. A lab change is not the same as a health benefit.	^{7 16}
Fasting blood glucose	Biological association	Low certainty	Measured in trials: unchanged in diabetes trials; lowered in one small trial. A lab change is not the same as a health benefit.	^{13 2}
Fasting insulin	Biological association	Low certainty	Measured in trials: small change. A lab change is not the same as a health benefit.	¹³
Triglycerides	Biological association	Very low certainty	Measured in trials: unchanged in pooled reviews; lowered in one small trial. A lab change is not the same as a health benefit.	^{2 13}

L. Active compounds

Connected to	Kind of connection	Evidence status	Context	Studies
Caffeine	Biological association	Human	Stimulates the central nervous system (EFSA); can raise heart rate and disturb sleep in sensitive people. Preparation or compound: Leaf	^{30 3 27 25}
Theaflavins	Biological association	Not established	Often named as a possible active in black tea; no human study in the sources read isolates their effect. Preparation or compound: Leaf	^{31 2}
Theaflavin 3,3'-digallate	Biological association	Not assessed	Not studied in the sources read. Preparation or compound: Leaf	³²
Thearubigins and other oxidation products	Biological association	Not assessed	A review notes that oxidation products of tea polyphenols differ greatly from one tea type to the next. None of the sources read measured thearubigins on their own. Preparation or compound: Leaf	²¹
Gallic acid derivatives, flavan-3-ols and flavonols	Biological association	Human	Polyphenols in tea bind iron and lower its absorption from a meal. Preparation or compound: Leaf	^{2 9}
L-Theanine	Biological association	Human	With caffeine, linked with small short-term gains in attention and mood in trials of the isolated compounds. Preparation or compound: Leaf	^{33 20}
Oxalate	Biological association	Human	Raises the question of kidney stones; trials and surveys disagree. Preparation or compound: Leaf (infusion)	²²

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 25, 2026).

Evidence at a glance: what the research found for 7 outcomes

4Low certainty

1Very low certainty

1Mixed findings

1Not enough evidence

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.

Cholesterol (LDL) 4 studies Mixed findings Blood pressure 4 studies Low certainty Heart disease and death rates in tea drinkers 3 studies Low certainty Risk of developing type 2 diabetes 1 study Low certainty Blood sugar in people with type 2 diabetes 1 study Low certainty Blood sugar and blood fats in healthy adults (one trial) 1 study Very low certainty Thinking, mood and focus 1 study Not enough evidence

The evidence

The research centre for Black Tea. 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 searched PubMed and read the abstracts of about 24 sources, read the FDA and NHS pages, the EFSA caffeine factsheet and the IARC press release, and checked the plant name in GBIF and compounds in PubChem. Only abstracts were read for papers. Certainty ratings are the compiler's own reading. No funding statement was read for most papers, so industry links are not ruled out. No study is cited that we could not verify.

Study library: every study we checked 34

Design Research type Year from Search

Study	Design	People	Product, dose, length	Result
Araya-Quintanilla 2019 Effectiveness of black tea versus placebo in subjects with hypercholesterolemia: A PRISMA systematic review and meta-analysis. Diabetes & metabolic syndrome · PMID 31235165 · DOI	Meta-analysis	6 randomised trials (7 met the criteria) of black tea versus placebo in adults with high cholesterol	Black tea leaf (drink) Differed Short term · vs Placebo	No significant difference between black tea and placebo for total cholesterol (mean difference 1.67 mg/dL, CI -5.47 to 8.80), triglycerides, LDL (CI -11.02 to 4.60) or HDL. The authors conclude that in the short term there was no difference in blood fats. No significant effect in people with high cholesterol (Total cholesterol MD 1.67 (-5.47, 8.80) mg/dL; LDL CI -11.02 to 4.60; HDL MD 0.38 (-1.12, 1.87)) Methods, limits and funding Outcomes: Total, LDL, HDL cholesterol and triglycerides Limitations: Few trials, short follow-up, number of people not given in the abstract. Funding and conflicts: Not stated in the abstract Read: abstract
Bahorun 2012 The effect of black tea on risk factors of cardiovascular disease in a normal population. Preventive medicine · PMID 22198621 · DOI	Controlled trial	Healthy adults in Mauritius; 71% in the tea group and 29% in the control group (numbers of people not given in the abstract)	Mauritian black tea, plain infusion without additives leaf (drink) Daily tea drinks (amounts not repeated here) 12 weeks plus a 3-week wash-out · vs Hot water	The tea group had a large fall in fasting glucose (18.4%, P<0.001) and triglycerides (35.8%, P<0.01), a fall in the LDL/HDL ratio (16.6%, P<0.05), a non-significant rise in HDL, and a large rise in a blood antioxidant measure (FRAP, 418%). The tea was rich in theaflavins and other polyphenols. Large changes in one small trial (Percent changes only; no confidence intervals in the abstract) Methods, limits and funding Outcomes: Fasting glucose, blood fats and antioxidant status Limitations: One trial, unequal group sizes, a hot-water control rather than a matching placebo tea, number of people and blinding not given in the abstract, and the size of the changes is unusually large compared with the pooled reviews, so it needs repeating. Funding and conflicts: Not stated in the abstract Read: abstract
Chin 2008 Caffeine content of brewed teas. Journal of analytical toxicology · PMID 19007524 · DOI	Food analysis n/a	20 assorted commercial tea products brewed under different conditions	Brewed teas (white, green, black, decaffeinated, herbal) leaf (drink) Lab measurement	Caffeine in white, green and black teas ranged from 14 to 61 mg per 6 or 8 oz serving, with no clear trend by variety. Decaffeinated teas contained under 12 mg, and no caffeine was detected in the herbal teas. Steep time changed the caffeine level. Most brewed teas had less caffeine per serving than brewed coffee. Wide range between products (n/a) Methods, limits and funding Outcomes: Caffeine in a serving Limitations: Only 20 products, one lab. Funding and conflicts: Not stated in the abstract Read: abstract
EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS) 2018 Scientific opinion on the safety of green tea catechins. EFSA journal. European Food Safety Authority · PMID 32625874 · DOI	Authoritative guidance	EU opinion on green tea catechins (green tea is not fermented; this is a different tea from black tea)	Green tea infusions and green tea catechin supplements leaf (drink) and extract	EFSA considered green tea infusions prepared in the traditional way generally safe at usual European intakes, but noted rare liver injury after infusions, most probably an individual reaction. It found that high-dose catechin food supplements raised liver enzymes in trials. This opinion is about green tea, not black tea. Rare liver injury; supplements raise liver enzymes at high doses (n/a) Methods, limits and funding Outcomes: Liver safety of green tea catechins Limitations: Abstract only; about green tea. Used here only to explain why extracts are a different product from a drink. Funding and conflicts: EFSA is a regulator; no industry funding Read: abstract
Haghighatdoost 2021 The Associations Between Tea and Coffee Drinking and Risk of Calcium-Oxalate Renal Stones. Plant foods for human nutrition (Dordrecht, Netherlands) · PMID 34735676 · DOI	Case control	430 215 newly diagnosed calcium-oxalate stone patients and 215 matched controls	Tea (type not specified in the abstract) leaf (drink) Usual glasses per day from a questionnaire Past-year intake · vs Controls	After adjustment, people drinking 4 or more glasses of tea a day had higher odds of calcium-oxalate stones than people drinking fewer than 2 (OR 2.73, 95% CI 1.50-4.99). Coffee was not linked once adjusted. The authors say coffee results are cautious because few people drank coffee. Higher odds of stones with 4+ glasses a day; association only (OR 2.73 (1.50, 4.99)) Methods, limits and funding Outcomes: Calcium-oxalate kidney stones Limitations: Case-control design with food questionnaire recall; one population; tea type and strength not described; cause not shown. Funding and conflicts: Not stated in the abstract Read: abstract
Hamitoğlu 2026 Assessment of the Potential Health Risks Associated with the Toxic and Essential Elements Content in Tea Samples Marketed in Türkiye. Turkish journal of pharmaceutical sciences · PMID 41960756 · DOI	Food analysis n/a	Dry leaves and infusions of 8 commercial black tea brands in Turkey	Black tea leaf and infusion leaf and infusion Lab measurement	Aluminium was the main toxic element in the dry leaf, followed by lead; arsenic and cadmium were lower. Metal levels in the infusions were significantly lower than in the dry leaf, so only part moves into the cup. All hazard scores for the infusions were below 1, but the cancer risk estimate for arsenic was in the moderate range, so the authors say arsenic needs continued monitoring. Tea contributed only a small share of daily mineral needs. The authors note the small sample. Infusions within safety limits except arsenic worth monitoring (Hazard quotients and hazard index below 1; arsenic ILCR 1e-6 to 1e-4) Methods, limits and funding Outcomes: Arsenic, aluminium, cadmium, lead and essential minerals; health risk scores Limitations: Eight brands from one country; model-based risk estimates. Funding and conflicts: Not stated in the abstract Read: abstract
Hartley 2013 Green and black tea for the primary prevention of cardiovascular disease. Cochrane Database of Systematic Reviews · PMID 23780706 · DOI	Systematic review	821 11 randomised trials of at least 3 months in healthy adults or adults at higher heart risk (4 of black tea, 7 of green tea)	Green tea, black tea or tea extracts (analysed separately); amounts and forms differed leaf (drink) and extracts Differed between trials At least 3 months; blood-pressure and LDL results over about 6 months · vs No intervention, placebo or minimal intervention	No trial reported heart or blood-vessel events. For black tea, LDL cholesterol fell by 0.43 mmol/L (95% CI -0.56 to -0.31) and systolic blood pressure by 1.85 mmHg (-3.21 to -0.48) over six months; diastolic pressure change was not significant (-1.27 mmHg, CI -3.06 to 0.53). Only a small number of trials fed each result and the trials were at risk of bias. The authors say the evidence is limited and results should be treated with caution. Small falls in LDL and systolic pressure for black tea (Black tea LDL MD -0.43 mmol/L (-0.56, -0.31); SBP MD -1.85 mmHg (-3.21, -0.48); DBP MD -1.27 (-3.06, 0.53)) Methods, limits and funding Outcomes: Heart events, blood pressure, cholesterol Limitations: Few trials per analysis, risk of bias, forms and amounts of tea differed; no heart-event data. Funding and conflicts: Non-US government support listed in the PubMed record; no industry funding stated in the abstract Read: abstract
Hu 2018 The safety of green tea and green tea extract consumption in adults - Results of a systematic review. Regulatory toxicology and pharmacology : RTP · PMID 29580974 · DOI	Systematic review	Toxicology studies and 159 human intervention studies of green tea and green tea extract	Green tea and green tea extract leaf (drink) and extract Differed Differed · vs Differed	Liver effects came from a limited range of concentrated, catechin-rich preparations taken in large single doses, not from brewed tea or extracts used in drinks or food. This review is about green tea, not black tea. Liver effects tied to concentrated preparations (n/a) Methods, limits and funding Outcomes: Safety of green tea preparations Limitations: About green tea; the authors derived intake levels that are not repeated here. Funding and conflicts: Not stated in the abstract Read: abstract
Hurrell 1999 Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages. The British journal of nutrition · PMID 10999016	Controlled trial	Adult volunteers eating a standard bread meal with radio-labelled iron	Black tea and other polyphenol drinks (herb teas, coffee, cocoa) leaf (drink) Servings with different polyphenol contents Single meals · vs Water control meal	Black tea reduced iron absorption from the bread meal by 79 to 94%. All the polyphenol drinks were potent inhibitors, and adding milk to tea or coffee had little or no effect on this. Large drop in iron absorption from one meal (Not given in the abstract) Methods, limits and funding Outcomes: Absorption of non-haem (plant-type) iron Limitations: Single test meals in a 1999 lab-style trial; says nothing about long-term iron status. Funding and conflicts: Not stated in the abstract Read: abstract
Igho-Osagie 2020 Short-Term Tea Consumption Is Not Associated with a Reduction in Blood Lipids or Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. The Journal of nutrition · PMID 33188386 · DOI	Meta-analysis	798 14 randomised trials of green and/or black tea for at least 4 weeks (4 to 24 weeks, average 7.4) in healthy adults and at-risk adults	Green tea or black tea (drink) leaf (drink) Differed 4 to 24 weeks · vs Placebo or control	No significant effect of tea on systolic or diastolic blood pressure or on any blood fat in healthy or at-risk adults. The reviewers rated the strength of evidence low to moderate and said many studies were too small to detect changes. No significant effect (Not significant for all outcomes (see paper)) Methods, limits and funding Outcomes: Blood pressure and blood fats (total, LDL, HDL, triglycerides) Limitations: Green and black tea were pooled in this paper, so it is not a black-tea-only result. Trials were short and underpowered. The review was registered (PROSPERO CRD42020134513). Funding and conflicts: Non-US government support listed in the PubMed record; no industry funding stated in the abstract Read: abstract
Jiang 2026 The association between tea consumption and hypertension: a systematic review and meta-analysis. Frontiers in nutrition · PMID 42694065 · DOI	Systematic review	319565 20 observational studies in adults: 16 cross-sectional studies and 4 cohort studies	Tea (any type; black tea was a subgroup) leaf (drink) Habitual intake Observational · vs People drinking less or no tea	In the 16 cross-sectional studies tea drinking was weakly linked to lower hypertension (OR 0.92, 95% CI 0.87-0.97). The link was stronger for black tea drinkers (the authors call this subgroup finding hypothesis-generating). The 4 cohort studies gave OR 0.87 (0.84-0.92). The authors say a clinical protective effect cannot be confirmed because of the observational design and marked variation between studies. Modestly lower odds of hypertension in drinkers; not proof of cause (Cross-sectional OR 0.92 (0.87, 0.97), I2 62.8%; cohort OR 0.87 (0.84, 0.92)) Methods, limits and funding Outcomes: Hypertension (high blood pressure) prevalence or risk Limitations: Observational; the effect measures are not identical so pooled values are only relative associations; large differences between studies; cause cannot be shown. Funding and conflicts: Not stated in the abstract Read: abstract
Kim 2024 Tea consumption and risk of all-cause, cardiovascular disease, and cancer mortality: a meta-analysis of thirty-eight prospective cohort data sets. Epidemiology and health · PMID 38938012 · DOI	Meta-analysis	1956549 38 prospective cohort data sets (27 papers) of adults	Tea (types not separated) leaf (drink) Highest versus lowest intake Cohort follow-up · vs Lowest intake categories	Highest versus lowest tea intake: all-cause death 0.90 (95% CI 0.86-0.95); heart and blood-vessel death 0.86 (0.79-0.94); cancer death 0.90 (0.78-1.03, not significant). The greatest risk reductions were around 1.5 to 2 cups a day, with no further gain beyond that for all-cause death. 10% lower all-cause and 14% lower heart-disease death with the highest intake; association only (All-cause ES 0.90 (0.86, 0.95); CVD ES 0.86 (0.79, 0.94); cancer ES 0.90 (0.78, 1.03)) Methods, limits and funding Outcomes: Death from any cause, from heart and blood-vessel disease, and from cancer Limitations: Observational, so cause is not shown. Tea types and preparation were not separated, so this is not a black-tea-only result. The authors call for better prospective studies. Funding and conflicts: Not stated in the abstract Read: abstract
Li 2016 Effects of tea or tea extract on metabolic profiles in patients with type 2 diabetes mellitus: a meta-analysis of ten randomized controlled trials. Diabetes/metabolism research and reviews · PMID 25689396 · DOI	Meta-analysis	608 10 randomised trials of tea or tea extract in adults with type 2 diabetes	Tea or tea extract (pooled) leaf (drink) and extract Differed Differed (waist result only in interventions longer than 8 weeks) · vs Control	Fasting blood glucose did not change (-0.05 mmol/L, 95% CI -0.51 to 0.40), nor did insulin resistance, LDL, HDL, triglycerides or blood pressure. Tea reduced the fall in fasting insulin (1.30 U/L, 0.36 to 2.24), and waist circumference fell by 2.70 cm only in trials longer than 8 weeks. No clear effect on blood sugar; small changes in fasting insulin and waist (Fasting glucose -0.05 mmol/L (-0.51, 0.40); fasting insulin 1.30 U/L (0.36, 2.24); waist -2.70 cm (-4.72, -0.69)) Methods, limits and funding Outcomes: Blood sugar, insulin, cholesterol, blood pressure, weight measures Limitations: Tea and extract are pooled, and the abstract does not say how much was black tea. Small trials. Funding and conflicts: Non-US government support listed in the PubMed record; no industry funding stated in the abstract Read: abstract
Li 2023 Daily higher tea consumption is associated with a reduced risk of type 2 diabetes: A cohort study and updated systematic review and meta-analysis. Nutrition research (New York, N.Y.) · PMID 37647847 · DOI	Meta-analysis	1076311 A cohort of 5,199 adults in China (1997 to 2009) plus a meta-analysis of 19 cohort studies	Tea (any variety; types not separated) leaf (drink) Self-reported tea drinking Cohort follow-up · vs Non-tea drinkers	In the authors' own cohort tea drinkers had a relative risk of type 2 diabetes of 1.02 (95% CI 0.82-1.28). In the meta-analysis of 19 cohorts there was no significant overall link (pooled RR 0.96, 0.91-1.00), but people who drank 4 or more cups a day had a 17% lower risk (RR 0.83, 0.76-0.90). No overall link; lower risk only at the highest intake, an association (Pooled RR 0.96 (0.91, 1.00); 4+ cups RR 0.83 (0.76, 0.90)) Methods, limits and funding Outcomes: New type 2 diabetes Limitations: Observational, tea types not separated, self-reported intake; high-intake people may differ in other habits. Funding and conflicts: Non-US government support listed in the PubMed record; no industry funding stated in the abstract Read: abstract
Liu 2026 Tea consumption and cardiovascular risk and outcomes: mechanistic insights, epidemiological evidence, and clinical implications. Frontiers in cardiovascular medicine · PMID 42755895 · DOI	Review	Narrative review of mechanisms, observational studies and trials	Tea (all types) leaf (drink) Differed	The reviewers say observational studies generally link habitual tea drinking with lower risk of hardening-of-the-arteries heart disease and death, but cause is uncertain: secondary-prevention data are limited, trials mainly measure surrogate markers, and Mendelian randomisation studies have not consistently supported a causal effect. They say current evidence does not support choosing a tea type for a disease or a standard therapeutic amount. Association only; cause not shown (n/a) Methods, limits and funding Outcomes: Heart and blood-vessel risk and outcomes Limitations: Narrative review, not a systematic pooling; tea types are not separated in the abstract. Funding and conflicts: Not stated in the abstract Read: abstract
Mahdavi-Roshan 2020 The effects of regular consumption of green or black tea beverage on blood pressure in those with elevated blood pressure or hypertension: A systematic review and meta-analysis. Complementary therapies in medicine · PMID 32507441 · DOI	Meta-analysis	408 5 randomised trials (9 measurements) of regular green or black tea drinks in adults with raised blood pressure or high blood pressure	Green or black tea (drink) leaf (drink) Differed Longer trials (3 months or more) showed larger falls · vs Control	Regular tea lowered systolic pressure by 4.81 mmHg (95% CI -8.40 to -1.58) and diastolic by 1.98 mmHg (-3.77 to -0.20). Without the most varied trials the falls were about 3.53 and 0.99 mmHg. The effect of green tea was more pronounced than that of black tea. No trial reported side effects. Small average falls; green tea stronger than black (SBP WMD -4.81 (-8.40, -1.58); DBP WMD -1.98 (-3.77, -0.20)) Methods, limits and funding Outcomes: Systolic and diastolic blood pressure Limitations: Only five trials; high variation between them; green and black tea pooled; two of five trials were not low risk of bias. Funding and conflicts: Not stated in the abstract Read: abstract
Małyszek 2025 Fluoride Content in Infusions of Selected Teas Available on the Polish Market-An In Vitro Study. Foods (Basel, Switzerland) · PMID 40724273 · DOI	Food analysis n/a	121 black tea samples on the Polish market (66 loose-leaf, 42 tea bags, 13 pyramid bags)	Black tea infusions leaf (drink) Lab measurement	Fluoride varied by tea form and origin. Tea-bag infusions had the highest fluoride and loose leaf the lowest. Teas from Africa had about twice as much fluoride as those from Central or East Asia. The authors say black tea, especially bags and African teas, may add a lot to daily fluoride intake and could exceed recommended levels for people drinking many cups or living in fluoridated areas. Fluoride varies widely between teas (n/a) Methods, limits and funding Outcomes: Fluoride, pH, calcium and phosphorus in infusions Limitations: One country's market; lab study of infusions; no health outcomes. Funding and conflicts: Not stated in the abstract Read: abstract
Małyszek 2025 Assessment of Fluoride Intake Risk via Infusions of Commercial Leaf Teas Available in Poland Using the Target Hazard Quotient Index Approach. Foods (Basel, Switzerland) · PMID 40941060 · DOI	Food analysis n/a	98 leaf teas on the Polish market (55 black, 27 green, 9 oolong, 7 white)	Leaf tea infusions leaf (drink) Lab measurement	Black teas had the lowest pH and the highest acidity, fluoride and phosphorus, especially teas from Africa and Central Asia. All fluoride hazard scores were well below the threshold (below 1), but the highest were in older adults of low body weight, particularly women drinking green tea. The authors say fluoride from leaf tea does not appear to pose a direct health risk, but older low-weight women may be more susceptible and should moderate high-fluoride teas. Hazard score below the threshold; higher in small older women (THQ < 1 for all) Methods, limits and funding Outcomes: Fluoride and a hazard score (target hazard quotient) Limitations: One country's market; hazard scores are model estimates, not measured harm. Funding and conflicts: Not stated in the abstract Read: abstract
Mennen 2007 Consumption of black, green and herbal tea and iron status in French adults. European journal of clinical nutrition · PMID 17299492 · DOI	Cross sectional	2593 954 men and 1,639 women in France (SU.VI.MAX), healthy adults	Black, green and herbal tea leaf (drink) Usual tea drinking by questionnaire Cross-sectional · vs Non-drinkers / lower drinkers	Serum ferritin was not related to black, green or herbal tea drinking in men or women, and the risk of iron depletion was not related to tea drinking, strength, infusion time or time of day. The authors conclude apparently healthy adults are not at risk of iron depletion from tea. No link in healthy adults (Not given in the abstract) Methods, limits and funding Outcomes: Blood ferritin (iron stores) and iron depletion Limitations: Cross-sectional; healthy French adults only; says nothing about people who already have low iron. Funding and conflicts: Not stated in the abstract Read: abstract
Payne 2025 Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrition reviews · PMID 40314930 · DOI	Meta-analysis	50 randomised trials in healthy people (15 eligible for at least one meta-analysis) of tea, L-theanine, or L-theanine plus caffeine	Tea (Camellia sinensis), L-theanine, or L-theanine plus caffeine leaf (drink) and isolated compounds Differed Mostly single doses · vs Placebo	The clearest small-to-moderate differences were for theanine plus caffeine against placebo in the first two hours (for example attention switching accuracy SMD 0.33, 95% CI 0.13-0.54). Theanine alone improved choice reaction time at hour 1 (SMD -0.35). The reviewers say the intervals often leave the size and direction uncertain, and that more research using tea drinks is needed. Small effects for theanine with caffeine; tea drinks themselves not shown (e.g. attention switching SMD 0.33 (0.13, 0.54); choice reaction time with theanine SMD -0.35 (-0.61, -0.10)) Methods, limits and funding Outcomes: Thinking, mood and sleep Limitations: Most trials tested isolated compounds, not tea; mostly short, single-dose tests in healthy people. Funding and conflicts: Not stated in the abstract Read: abstract
Rothenberg 2018 A Review on the Weight-Loss Effects of Oxidized Tea Polyphenols. Molecules (Basel, Switzerland) · PMID 29758009 · DOI	Review	Review of how oxidised tea polyphenols might affect body weight	Fermented (black, oolong, dark) and unfermented teas leaf	The authors put forward their own "short-chain fatty acid hypothesis": tea polyphenols block carbohydrate-digesting enzymes and interact with gut bacteria, which could change fat metabolism. They say some evidence suggests fermented teas trigger this more than unfermented ones, and that results are inconsistent. Hypothesis, not a human result (n/a) Methods, limits and funding Outcomes: Weight-loss mechanisms (hypothesis) Limitations: A mechanism review proposing the authors' own hypothesis; not a trial. Funding and conflicts: Not stated in the abstract Read: abstract
Siener 2021 Effect of Black Tea Consumption on Urinary Risk Factors for Kidney Stone Formation. Nutrients · PMID 34959987 · DOI	Controlled trial	10 10 healthy men on a standard diet	Black tea leaf (drink) Fixed daily volume during the black tea days Ten days in all: five days of fruit tea as the control, then five days of black tea · vs Fruit tea (no oxalate) in the first phase of the same men	Black tea did not significantly change 24-hour urinary oxalate. Urinary citrate, which helps protect against calcium stones, increased significantly, and the stone-risk saturation measures stayed the same. The authors conclude no raised risk of kidney stones could be shown in normal subjects and say people who absorb too much oxalate need more study. No rise in urine oxalate in healthy men (Not given in the abstract) Methods, limits and funding Outcomes: 24-hour urine oxalate, citrate and stone-risk measures Limitations: Ten healthy men only, short, no stone formers; not a trial of stones themselves. Funding and conflicts: Not stated in the abstract Read: abstract
Wu 2024 Habitual tea consumption is associated with a lower prevalence of kidney stone disease in postmenopausal women. PeerJ · PMID 39677960 · DOI	Cross sectional	11484 11,484 postmenopausal women in the Taiwan Biobank	Tea (type not specified in the abstract) leaf (drink) Habitual tea drinking versus none, by questionnaire Cross-sectional · vs Non-tea drinkers	Habitual tea drinkers had lower prevalence of kidney stones (7% vs 5%); adjusted odds ratio 0.78 (95% CI 0.63-0.96). Women drinking two cups or more a day had OR 0.71 (0.56-0.90). Lower stone prevalence in drinkers; association only (OR 0.78 (0.63, 0.96); two cups or more OR 0.71 (0.56, 0.90)) Methods, limits and funding Outcomes: Kidney stone disease Limitations: Cross-sectional questionnaire study in postmenopausal women in Taiwan; cause not shown; tea type not specified. Funding and conflicts: Non-US government support listed in the PubMed record; no industry funding stated in the abstract Read: abstract
Zhao 2015 Black tea consumption and serum cholesterol concentration: Systematic review and meta-analysis of randomized controlled trials. Clinical nutrition (Edinburgh, Scotland) · PMID 24972454 · DOI	Meta-analysis	411 10 randomised trials of black tea drinking; adults, with and without higher heart risk	Black tea drink leaf (drink) Differed between trials Differed · vs Placebo or control drink (per review)	LDL cholesterol fell by 4.64 mg/dL (95% CI -8.99 to -0.30; P = 0.036). Total cholesterol (-2.04 mg/dL) and HDL (-1.15 mg/dL) did not change clearly. The LDL fall was larger in people at higher heart risk. Small fall in LDL; none in total or HDL (LDL -4.64 (-8.99, -0.30) mg/dL; total -2.04 (-6.43, 2.35); HDL -1.15 (-3.04, 0.75)) Methods, limits and funding Outcomes: Total, LDL and HDL cholesterol Limitations: Small total sample; the abstract gives no certainty grade; the LDL interval almost reaches zero. Funding and conflicts: Non-US government support listed in the PubMed record; no industry funding stated in the abstract Read: abstract
n/a 2015 EFSA: Caffeine, EFSA explains risk assessment (factsheet, 2015) n/a · Source	Authoritative guidance n/a	n/a	n/a	Said above. Methods, limits and funding Outcomes: Says single doses of caffeine up to 200 mg from all sources do not raise safety concerns for healthy adults; single doses of 100 mg may affect sleep in some adults, particularly close to bedtime; intakes up to 400 mg a day do not raise concerns for healthy adults other than pregnant women; up to 200 mg a day does not raise concerns for the foetus. Notes tea was the main caffeine source in the UK and Ireland. Limitations: A factsheet summarising a scientific opinion; the full opinion was not opened. Text of the PDF read on 2026-10-25. Read: full-text
n/a 2016 IARC (WHO): Press release no. 244, IARC Monographs evaluate drinking coffee, mate, and very hot beverages (15 June 2016) n/a · Source	Authoritative guidance n/a	n/a	n/a	Said above. Methods, limits and funding Outcomes: Classed drinking very hot beverages (above about 65 C) as probably carcinogenic to humans (Group 2A) for cancer of the oesophagus, based on limited human evidence from places where tea or mate is traditionally drunk very hot. Says the temperature, not the drink, appears responsible. Limitations: A press release; the full journal summary was not opened. Text read on 2026-10-25. Read: full-text
n/a 2024 FDA: Spilling the Beans: How Much Caffeine Is Too Much? (content current as of 28 Aug 2024) n/a · Source	Authoritative guidance n/a	n/a	n/a	Said above. Methods, limits and funding Outcomes: Lists black tea at 71 mg caffeine and green tea at 37 mg in a 12 fl oz drink. Says about 400 mg a day is not generally linked with negative effects in most adults, with wide differences in sensitivity and some medicines raising sensitivity. Lists signs of too much caffeine. Advises people who are pregnant, trying to become pregnant or breastfeeding to ask their health care provider whether to limit caffeine. Quotes the Dietary Guidelines that caffeinated drinks should be avoided for children younger than 2. Says decaffeinated tea still has some caffeine. Limitations: A consumer update, not a trial. Page text read on 2026-10-25. Read: full-text
n/a 2024 NHS (UK): Iron deficiency anaemia (page last reviewed 26 January 2024) n/a · Source	Authoritative guidance n/a	n/a	n/a	Said above. Methods, limits and funding Outcomes: Under "things you can do", tells people with iron deficiency anaemia to eat and drink less tea, coffee, and dairy foods and high-phytic-acid foods, because large amounts of these make it harder to absorb iron from food and tablets. Limitations: A public-health page, not a trial. Page text read on 2026-10-25. Read: full-text
n/a 2026 NHS (UK): Foods to avoid in pregnancy (page last reviewed 15 June 2026) n/a · Source	Authoritative guidance n/a	n/a	n/a	Said above. Methods, limits and funding Outcomes: Says not to have more than 200 mg of caffeine a day in pregnancy, lists about 75 mg in a cup of tea (black or green), and says too much caffeine has been linked to a higher chance of miscarriage and stillbirth. Limitations: A public-health page, not a trial. Page text read on 2026-10-25. Read: full-text
n/a 2026 PubChem: Caffeine (CID 2519) n/a · Source	Database record n/a	n/a	n/a	Identity record only. Methods, limits and funding Outcomes: Caffeine, formula C8H10N4O2. Limitations: Database record, checked 2026-10-25. Read: full-text
n/a 2026 PubChem: Theaflavin (CID 135403798) n/a · Source	Database record n/a	n/a	n/a	Identity record only. Methods, limits and funding Outcomes: Theaflavin, formula C29H24O12. Limitations: Database record, checked 2026-10-25. Read: full-text
n/a 2026 PubChem: Theaflavin 3,3'-digallate (CID 135536164) n/a · Source	Database record n/a	n/a	n/a	Identity record only. Methods, limits and funding Outcomes: Theaflavin 3,3'-digallate, formula C43H32O20. Limitations: Database record, checked 2026-10-25. Read: full-text
n/a 2026 PubChem: L-Theanine (CID 439378) n/a · Source	Database record n/a	n/a	n/a	Identity record only. Methods, limits and funding Outcomes: L-Theanine, formula C7H14N2O3. Limitations: Database record, checked 2026-10-25. Read: full-text
n/a 2026 GBIF Backbone Taxonomy: Camellia sinensis (L.) Kuntze (usage key 3189635) n/a · Source	Database record n/a	n/a	n/a	Accepted species, family Theaceae, order Ericales. Methods, limits and funding Outcomes: Accepted species Camellia sinensis (L.) Kuntze, family Theaceae, order Ericales. Limitations: Taxonomic database record via the GBIF API, checked 2026-10-25. Read: full-text

What we do not know yet

What the evidence supports: small and mixed effects on cholesterol and blood pressure; no clear effect on blood sugar in trials; links with lower death rates that cannot show cause.
No long-term trial of black tea as a drink with heart attack, stroke or death as outcomes.
Most reviews pool green and black tea or all tea types, so black-tea-only results are few.
No black tea drug interaction was found in the sources read; no black tea extract safety study was found.
Funding statements were not stated in most abstracts, so industry links are not ruled out; EMA, NCCIH, LiverTox and Health Canada pages for black tea were not opened.

How new research is added

New studies are found by a saved PubMed search and are placed in a review queue. A person reads each one before it changes any evidence rating or safety wording. New publications never change ratings automatically.

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".

Metabolic 5

●

LDL cholesterol

Lowered in some reviews in trials

The cholesterol carried in the blood that is linked with higher heart disease risk.

Mixed findings

Results and what it means

Why it was measured

To see whether black tea changes blood fats.

Statistical vs. clinical meaning

Small and inconsistent; a lab number, not a heart outcome.

Safety implication

None from the numbers; see the Safety tab for caffeine and iron.

Study	Result	People	Product
²⁴	LDL -4.64 mg/dL (95% CI -8.99 to -0.30)	Adults in 10 trials	Black tea drink
⁷	LDL MD -0.43 mmol/L (-0.56 to -0.31) for black tea	Adults in 4 black tea trials	Black tea drink
¹	No significant difference from placebo	Adults with high cholesterol in 6 trials	Black tea
¹⁰	No significant effect on LDL	Healthy and at-risk adults in 14 trials	Green and/or black tea

^{24 7 1 10}

●

Total cholesterol

Unchanged in trials

All the cholesterol carried in the blood, including LDL and HDL.

Low certainty

Results and what it means

Why it was measured

A broad measure of blood fats.

Statistical vs. clinical meaning

No clear effect on total or HDL cholesterol.

Safety implication

None.

Study	Result	People	Product
²⁴	Total -2.04 mg/dL (95% CI -6.43 to 2.35), not significant; HDL -1.15 (-3.04 to 0.75), not significant	Adults in 10 trials	Black tea drink
¹	Total MD 1.67 mg/dL (-5.47 to 8.80), not significant	Adults with high cholesterol in 6 trials	Black tea

^{24 1}

●

Fasting blood glucose

Unchanged in diabetes trials; lowered in one small trial in trials

Blood sugar measured after not eating overnight.

Low certainty

Results and what it means

Why it was measured

To see whether black tea changes blood sugar.

Statistical vs. clinical meaning

The pooled review found no effect; the single trial is far larger and unconfirmed.

Safety implication

None from the numbers.

Study	Result	People	Product
¹³	-0.05 mmol/L (95% CI -0.51 to 0.40), not significant	608 adults with type 2 diabetes in 10 trials	Tea or tea extract
²	Fell 18.4% (P<0.001)	Healthy adults in one 12-week trial	Black tea infusion versus hot water

^{13 2}

●

Fasting insulin

Small change in trials

Insulin measured in the blood after not eating overnight.

Low certainty

Results and what it means

Why it was measured

A marker of how hard the body works to control sugar.

Statistical vs. clinical meaning

A small change in a lab marker only.

Safety implication

None.

Study	Result	People	Product
¹³	Tea reduced the fall in fasting insulin (1.30 U/L, 95% CI 0.36 to 2.24); insulin resistance (HOMA-IR) not significant	608 adults with type 2 diabetes	Tea or tea extract

¹³

●

Triglycerides

Unchanged in pooled reviews; lowered in one small trial in trials

A type of fat in the blood.

Very low certainty

Results and what it means

Why it was measured

A blood fat linked with heart and metabolic health.

Statistical vs. clinical meaning

Two sources disagree; the larger fall comes from one unconfirmed trial.

Safety implication

None.

Study	Result	People	Product
²	Fell 35.8% (P<0.01)	Healthy adults in one 12-week trial	Black tea infusion versus hot water
¹³	-0.11 mmol/L (-0.28 to 0.05), not significant	Adults with type 2 diabetes	Tea or tea extract

^{2 13}

Other 2

●

Systolic blood pressure

Lowered slightly in some reviews in trials

The top number in a blood pressure reading, the pressure when the heart beats.

Low certainty

Results and what it means

Why it was measured

To see whether regular tea drinking changes blood pressure.

Statistical vs. clinical meaning

Small and inconsistent.

Safety implication

Caffeine can raise blood pressure briefly in some people.

Study	Result	People	Product
⁷	SBP MD -1.85 mmHg (-3.21 to -0.48) for black tea	Adults in black tea trials	Black tea drink
¹⁶	SBP -4.81 mmHg (-8.40 to -1.58); green tea stronger than black	408 adults with raised or high blood pressure in 5 trials	Green or black tea drink
¹⁰	No significant effect	798 adults in 14 trials	Green and/or black tea

^{7 16 10}

●

Diastolic blood pressure

Unchanged or lowered slightly in trials

The bottom number in a blood pressure reading, the pressure between heartbeats.

Low certainty

Results and what it means

Why it was measured

The second part of a blood pressure reading.

Statistical vs. clinical meaning

Even smaller than systolic changes.

Safety implication

None from the numbers.

Study	Result	People	Product
⁷	DBP MD -1.27 mmHg (-3.06 to 0.53), not significant for black tea	Adults in black tea trials	Black tea drink
¹⁶	DBP -1.98 mmHg (-3.77 to -0.20)	408 adults with raised or high blood pressure	Green or black tea drink

^{7 16}

Safety

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

Main points to know 8

A cup of black tea is not the same as a tea extract or supplement. This page is about black tea as a drink. Concentrated tea extracts, powders and capsules are a different product. The liver warnings that exist for tea extracts come from green tea catechin supplements: EFSA found rare liver injury after green tea infusions and raised liver enzymes with high-dose catechin supplements, and a review of 159 human studies tied liver effects to concentrated, catechin-rich preparations rather than brewed tea. No safety study of black tea extract capsules was found in the sources read, so nothing here covers them. Do not carry results from one form to the other. Authoritative guidance ^{4 8}
Caffeine. Black tea contains caffeine. A lab study of 20 products found 14 to 61 mg per serving in white, green and black teas, and the FDA lists black tea at 71 mg in a 12 fl oz drink. The FDA says about 400 mg a day from all sources is not generally linked with negative effects in most adults, but people differ a lot in how sensitive they are and some medicines raise sensitivity. EFSA says a single 100 mg dose of caffeine may affect sleep in some adults, particularly close to bedtime. Decaffeinated tea still has a little caffeine. Authoritative guidance ^{27 25 3}
Tea can block iron absorption. In a trial using a bread meal, black tea cut absorption of non-haem iron by 79 to 94%, and milk made little difference. The NHS tells people with iron deficiency anaemia to eat and drink less tea. A French study of healthy adults found no link between tea drinking and iron stores, so the concern is mainly for people with low iron, pregnant people and those at risk of anaemia. Controlled trial ^{9 28 19}
Pregnancy: caffeine limit. Tea counts toward the daily caffeine limit. The NHS says not to have more than 200 mg of caffeine a day in pregnancy and counts about 75 mg in a cup of tea. EFSA says up to 200 mg a day from all sources does not raise safety concerns for the foetus. The NHS links too much caffeine with a higher chance of miscarriage and stillbirth. Authoritative guidance ^{29 25}
Very hot tea. The International Agency for Research on Cancer (IARC) classed drinking very hot beverages (above about 65 C) as probably carcinogenic to the oesophagus. It said the temperature, not the drink, appears responsible. The evidence came from places where tea or mate is traditionally drunk very hot. Authoritative guidance ²⁶
Kidney stones: studies disagree. Black tea contains oxalate. In a small trial of 10 healthy men it did not raise urinary oxalate. A case-control study linked 4 or more glasses of tea a day with more calcium-oxalate stones (OR 2.73), while a Taiwan study in postmenopausal women found fewer stones in tea drinkers. If you have had kidney stones, ask your doctor about tea. Mixed ^{22 5 23}
Fluoride and metals depend on the tea. Tea plants take up fluoride. A study of 121 black teas found the most fluoride in tea-bag infusions, and about twice as much in teas from Africa as from Central or East Asia. A second study found all hazard scores below the safety threshold, but highest in older, low-weight women. A study of 8 brands found metals lower in the cup than in the dry leaf and within limits, with arsenic worth monitoring. Food analysis ^{17 18 6}
Babies and young children. The FDA quotes the Dietary Guidelines that caffeinated drinks should be avoided for children younger than 2. No source read gives tea advice for older children, so ask a paediatrician. Authoritative guidance ²⁷

Side effects 5

Effect	How often	Severity and recovery	Evidence
Caffeine effects: fast or pounding heartbeat, jitters, anxiety, poor sleep, upset stomach, headache Listed by the FDA as signs of too much caffeine from any source. The FDA also says withdrawal from regular caffeine is not dangerous but can be unpleasant.	Depends on how much caffeine you have from all sources and how sensitive you are; no rate was found for black tea.	mild to moderate Usually settles when caffeine is cut back	Authoritative guidance ²⁷
Sleep disturbance A single 100 mg caffeine dose may affect sleep duration and pattern in some adults.	Some adults, especially if caffeine is taken close to bedtime (EFSA).	mild Reversible	Authoritative guidance ²⁵
Lower iron absorption from a meal The NHS advises people with iron deficiency anaemia to eat and drink less tea.	Large effect on one test meal (79 to 94%); no link with iron stores in healthy French adults.	matters most if iron is already low Reversible	Controlled trial ^{9 19 28}
Kidney stone risk (unclear) A trial showed no rise in urine oxalate; a case-control study linked 4 or more glasses a day with more stones.	Studies disagree; no rate found.	not established Not described	Mixed ^{22 5 23}
Fluoride intake The authors say people drinking many cups, or living where water is fluoridated, could exceed recommended levels, and that older low-weight women may be more susceptible.	Varies with tea form and origin; hazard scores were below the threshold in one study.	not established for ordinary use Not described	Food analysis ^{17 18}

Liver

No report of liver injury from black tea as a drink was found in the sources read. Liver injury is documented for green tea catechin extracts and rarely after green tea infusions (EFSA); that is a different tea and a different product. No source read describes liver injury from black tea extract. ^{4 8}

How often. No rate for black tea was found. The green tea findings are not applied to black tea.

Monitoring. No monitoring advice for black tea was read. If you use any concentrated tea product and notice yellow skin or eyes, dark urine or severe tiredness, stop it and get medical help.

This is a safety connection. It is not evidence that Black Tea supports liver health.

Medicines and supplements 4

With	Why it matters	Importance	Evidence	What to do
Iron tablets and iron-rich meals supplement	Tea polyphenols bind iron from food and lower absorption; black tea reduced absorption from a bread meal by 79 to 94%.	Matters if you are treating or at risk of iron deficiency.	Controlled trial Moderate certainty ^{9 28}	The NHS tells people with iron deficiency anaemia to eat and drink less tea. Ask your pharmacist or doctor about timing of tea and iron.
Medicines and stimulants that also affect the heart, nerves or sleep general caffeine	Black tea contains caffeine. The FDA says some medications can make people more sensitive to caffeine.	Not specific to black tea; no drug-by-drug list for black tea was read.	Authoritative guidance Low certainty ²⁷	If you take medicines, ask your pharmacist whether caffeine matters for you.
Warfarin and other medicines for blood clots prescription	No source read describes an interaction between black tea as a drink and warfarin. A case report exists for large amounts of green tea, which is a different tea and was not re-read here.	Not established for black tea.	Insufficient Not enough evidence	Tell your prescriber about any big change in your tea habits so blood tests can be timed.
Concentrated tea extracts and supplements supplement	A cup of tea and a concentrated extract are different products. Green tea extracts have documented liver effects at high doses (EFSA); nothing equivalent was found for black tea extract.	Not established for black tea extract.	Authoritative guidance Not enough evidence ^{4 8}	Ask a pharmacist or doctor before taking any concentrated tea product.

Who should check first 6

Situation	Advice	Evidence
Pregnancy	Black tea is not banned, but its caffeine counts toward the daily limit (NHS 200 mg a day in pregnancy; about 75 mg in a cup of tea). EFSA says up to 200 mg a day from all sources does not raise concerns for the foetus. Ask your midwife or doctor.	Authoritative guidance ^{29 25}
Breastfeeding	The FDA suggests people who are breastfeeding ask their health care provider whether to limit caffeine. No breastfeeding-specific tea source was read beyond that.	Authoritative guidance ²⁷
Iron deficiency anaemia or low iron	The NHS advises eating and drinking less tea. Ask your doctor about iron and tea.	Authoritative guidance ^{28 9}
Past kidney stones	Results on tea and stones disagree. Ask your doctor or kidney specialist.	Mixed ^{22 5 23}
Trouble sleeping, anxiety, fast heartbeat or other caffeine sensitivity	Black tea contains caffeine. The FDA lists signs of too much caffeine and says sensitivity varies. Talk to a doctor if tea brings these on.	Authoritative guidance ^{27 25}
Children under 2	The FDA quotes the Dietary Guidelines that drinks with caffeine should be avoided for children younger than 2.	Authoritative guidance ²⁷

Overdose, product quality and regulators

Summary. No poisoning from ordinary black tea drinking was described in the sources read. The risks that were found are about caffeine, iron absorption and very hot drinks.

Animal. Not read.

Human doses studied. Not covered. This page gives no amounts.

High dose or long term signals. Heavy drinking raises the questions about caffeine, fluoride and kidney stones listed above; none of the studies read shows harm in ordinary use.

Overdose response. Not described in the sources read. The FDA notes that pure and highly concentrated caffeine products are a separate danger and have caused serious harm, including death; they are not tea.

Genotoxicity. Not read.

Toxic or hazardous parts. The leaf is the part used. No source read describes a toxic part of the tea plant.

Quality findings come from food analyses of fluoride and metals, not from tests of adverse effects.

Fluoride. A study of 121 Polish black teas found fluoride highest in tea-bag infusions and lowest in loose leaf, and about twice as high in African teas as in Central or East Asian teas. A second study of 98 leaf teas found all fluoride hazard scores below the threshold, with the highest in older low-weight women. ^{17 18}

Aluminium, lead, arsenic and cadmium. A Turkish study of 8 black tea brands found aluminium the main toxic element in the dry leaf, then lead, with lower arsenic and cadmium. Infusions had significantly lower levels than leaf, hazard scores were below 1, and the authors say arsenic needs continued monitoring. Eight brands is a small sample. ⁶

Pesticides and flavoured teas. No pesticide figures or data on flavoured teas were read.

Body	Action	Date
US FDA (United States)	Consumer update on caffeine: black tea 71 mg per 12 fl oz; about 400 mg a day not generally linked with negative effects in most adults; lists signs of too much caffeine; avoid caffeinated drinks for children under 2 (quoting the Dietary Guidelines). source	2024-08-28
NHS (United Kingdom)	Pregnancy: no more than 200 mg of caffeine a day; about 75 mg in a cup of tea. source	2026-06-15
NHS (United Kingdom)	People with iron deficiency anaemia should eat and drink less tea, coffee and dairy foods, which make it harder to absorb iron. source	2024-01-26
EFSA (European Union)	Caffeine factsheet: up to 400 mg a day from all sources does not raise safety concerns for healthy adults except pregnant women; up to 200 mg a day does not raise concerns for the foetus; a single 100 mg dose may affect sleep in some adults. source	2015-05
IARC (WHO) (International)	Very hot beverages probably carcinogenic to humans (Group 2A) for the oesophagus; temperature, not the drink, appears responsible. source	2016-06-15
EFSA (European Union)	Opinion on green tea catechins (not black tea): traditional infusions generally considered safe at European intakes; rare liver injury after infusions; high-dose catechin supplements raised liver enzymes. source	2018-04

When to get medical help

A racing or irregular heartbeat, chest pain, fainting or severe anxiety after tea or any caffeine.
Yellow skin or eyes, dark urine, pale stools or severe itching if you use any concentrated tea product.
Severe tiredness, breathlessness or pale skin if you have anaemia.
Pain in the side or back, blood in the urine or fever if you have a history of kidney stones.

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 black tea?

Black tea is a drink made from the leaves of the tea plant, Camellia sinensis, after the leaves are fully oxidised (often called fermented). Green, oolong and white tea come from the same plant but are processed differently. The drink contains caffeine and theaflavins.

^{34 21}

Is black tea the same as a tea extract or supplement?

No. A cup of tea is a weak water extract. Extracts, powders and capsules are concentrated products. Liver warnings exist for green tea catechin extracts (EFSA); nothing equivalent was read for black tea extract, so the page makes no claim about it. Do not carry results from one product to the other.

^{4 8}

Does black tea lower cholesterol?

Maybe slightly, but reviews disagree. A pooled analysis of 10 trials found LDL cholesterol 4.64 mg/dL lower and Cochrane found a fall in black tea trials. A review in people with high cholesterol and a review of 14 short trials found no significant effect.

^{24 7 1 10}

Does black tea lower blood pressure?

Small falls have been reported. Cochrane found about 1.85 mmHg lower systolic pressure with black tea. A review of green or black tea found larger falls with green stronger than black, and a review of 14 short trials found none. Do not use tea in place of blood pressure treatment.

^{7 16 10 11}

Do people who drink black tea live longer or have fewer heart problems?

In 38 cohort data sets, the highest tea intake was linked with about 10% lower all-cause and 14% lower heart-disease death. This is an association; tea types were not separated and cause is uncertain. No trial of black tea has measured heart attacks, strokes or deaths.

^{12 15 7}

Does black tea help with diabetes or blood sugar?

Not clearly. Ten trials of tea or tea extract in people with type 2 diabetes found no significant change in fasting blood sugar. A cohort meta-analysis found no clear overall link with developing diabetes. Talk to your doctor before changing diabetes care.

^{13 14}

Does black tea help focus, memory or mood?

Not shown for the drink itself. A review of 50 trials found small gains mainly for L-theanine plus caffeine as isolated compounds, mostly in short tests. The reviewers ask for more trials using actual tea.

²⁰

Does black tea have caffeine, and can it affect sleep?

Yes. A lab study found 14 to 61 mg per serving in white, green and black teas, and the FDA lists 71 mg in a 12 fl oz cup. Caffeine can cause jitters and fast heartbeat, and EFSA says it may affect sleep in some adults, especially near bedtime. Sensitivity varies and some medicines raise it.

^{3 27 25}

Does tea affect iron?

It can. Black tea reduced iron absorption from a test meal by 79 to 94%, and the NHS tells people with iron deficiency anaemia to eat and drink less tea. A French study of healthy adults found no link between tea drinking and iron stores.

^{9 28 19}

Is black tea safe in pregnancy, breastfeeding or for children?

It counts toward your caffeine limit. The NHS says no more than 200 mg of caffeine a day in pregnancy and counts about 75 mg in a cup of tea, and EFSA says up to 200 mg a day does not raise concerns for the foetus. The FDA suggests asking a health care provider about caffeine while breastfeeding and quotes guidance to avoid caffeinated drinks for children under 2. Ask a clinician.

^{29 25 27}

Can black tea cause kidney stones?

Studies disagree. A small trial in healthy men found no rise in urine oxalate, a case-control study linked 4 or more glasses of tea a day with more calcium-oxalate stones, and a Taiwan study of postmenopausal women found fewer stones in tea drinkers. If you have had stones, ask your doctor.

^{22 5 23}

Is very hot tea a problem, and what about fluoride or metals?

IARC classed very hot beverages as probably carcinogenic to the oesophagus, and said it is the temperature, not the drink. Fluoride is highest in tea-bag infusions and African teas in a Polish study, with hazard scores below the threshold. A Turkish study found metals within limits, with arsenic worth monitoring.

^{26 17 18 6}

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Editorial transparency

Written by: AlternativeMed editorial team. Research compiled with AI assistance, then checked against PubMed records.
Medical review: None. This page has not been reviewed by a physician or pharmacist.
First published: 2026-10-25
Last substantive update: 2026-10-25
How we research: We searched PubMed and read the abstracts of about 24 sources, read the FDA and NHS pages, the EFSA caffeine factsheet and the IARC press release, and checked the plant name in GBIF and compounds in PubChem. Only abstracts were read for papers. Certainty ratings are the compiler's own reading. No funding statement was read for most papers, so industry links are not ruled out. No study is cited that we could not verify.
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. This page is information, not a recommendation to drink or take anything.

Sources 34

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

Araya-Quintanilla F, Gutiérrez-Espinoza H, Moyano-Gálvez V, et al. Effectiveness of black tea versus placebo in subjects with hypercholesterolemia: A PRISMA systematic review and meta-analysis.. Diabetes & metabolic syndrome. 2019. PMID 31235165. DOI 10.1016/j.dsx.2019.05.019. (abstract)
Bahorun T, Luximon-Ramma A, Neergheen-Bhujun VS, et al. The effect of black tea on risk factors of cardiovascular disease in a normal population.. Preventive medicine. 2012. PMID 22198621. DOI 10.1016/j.ypmed.2011.12.009. (abstract)
Chin JM, Merves ML, Goldberger BA, et al. Caffeine content of brewed teas.. Journal of analytical toxicology. 2008. PMID 19007524. DOI 10.1093/jat/32.8.702. (abstract)
EFSA Panel on Food Additives and Nutrient Sources added to Food (ANS). Scientific opinion on the safety of green tea catechins.. EFSA journal. European Food Safety Authority. 2018. PMID 32625874. DOI 10.2903/j.efsa.2018.5239. (abstract)
Haghighatdoost F, Sadeghian R, Abbasi B. The Associations Between Tea and Coffee Drinking and Risk of Calcium-Oxalate Renal Stones.. Plant foods for human nutrition (Dordrecht, Netherlands). 2021. PMID 34735676. DOI 10.1007/s11130-021-00933-4. (abstract)
Hamitoğlu M, Şahin M, Esen G, et al. Assessment of the Potential Health Risks Associated with the Toxic and Essential Elements Content in Tea Samples Marketed in Türkiye.. Turkish journal of pharmaceutical sciences. 2026. PMID 41960756. DOI 10.4274/tjps.galenos.2026.86132. (abstract)
Hartley L, Flowers N, Holmes J, et al. Green and black tea for the primary prevention of cardiovascular disease.. Cochrane Database of Systematic Reviews. 2013. PMID 23780706. DOI 10.1002/14651858.CD009934.pub2. (abstract)
Hu J, Webster D, Cao J, et al. The safety of green tea and green tea extract consumption in adults - Results of a systematic review.. Regulatory toxicology and pharmacology : RTP. 2018. PMID 29580974. DOI 10.1016/j.yrtph.2018.03.019. (abstract)
Hurrell RF, Reddy M, Cook JD. Inhibition of non-haem iron absorption in man by polyphenolic-containing beverages.. The British journal of nutrition. 1999. PMID 10999016. (abstract)
Igho-Osagie E, Cara K, Wang D, et al. Short-Term Tea Consumption Is Not Associated with a Reduction in Blood Lipids or Pressure: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.. The Journal of nutrition. 2020. PMID 33188386. DOI 10.1093/jn/nxaa295. (abstract)
Jiang R, Chen J, Lin H, et al. The association between tea consumption and hypertension: a systematic review and meta-analysis.. Frontiers in nutrition. 2026. PMID 42694065. DOI 10.3389/fnut.2026.1883708. (abstract)
Kim Y, Je Y. Tea consumption and risk of all-cause, cardiovascular disease, and cancer mortality: a meta-analysis of thirty-eight prospective cohort data sets.. Epidemiology and health. 2024. PMID 38938012. DOI 10.4178/epih.e2024056. (abstract)
Li Y, Wang C, Huai Q, et al. Effects of tea or tea extract on metabolic profiles in patients with type 2 diabetes mellitus: a meta-analysis of ten randomized controlled trials.. Diabetes/metabolism research and reviews. 2016. PMID 25689396. DOI 10.1002/dmrr.2641. (abstract)
Li X, Zeng J, Chen B, et al. Daily higher tea consumption is associated with a reduced risk of type 2 diabetes: A cohort study and updated systematic review and meta-analysis.. Nutrition research (New York, N.Y.). 2023. PMID 37647847. DOI 10.1016/j.nutres.2023.08.002. (abstract)
Liu R, Li J, Liang Y. Tea consumption and cardiovascular risk and outcomes: mechanistic insights, epidemiological evidence, and clinical implications.. Frontiers in cardiovascular medicine. 2026. PMID 42755895. DOI 10.3389/fcvm.2026.1913976. (abstract)
Mahdavi-Roshan M, Salari A, Ghorbani Z, et al. The effects of regular consumption of green or black tea beverage on blood pressure in those with elevated blood pressure or hypertension: A systematic review and meta-analysis.. Complementary therapies in medicine. 2020. PMID 32507441. DOI 10.1016/j.ctim.2020.102430. (abstract)
Małyszek A, Zawiślak I, Kulus M, et al. Fluoride Content in Infusions of Selected Teas Available on the Polish Market-An In Vitro Study.. Foods (Basel, Switzerland). 2025. PMID 40724273. DOI 10.3390/foods14142452. (abstract)
Małyszek A, Zawiślak I, Kulus M, et al. Assessment of Fluoride Intake Risk via Infusions of Commercial Leaf Teas Available in Poland Using the Target Hazard Quotient Index Approach.. Foods (Basel, Switzerland). 2025. PMID 40941060. DOI 10.3390/foods14172944. (abstract)
Mennen L, Hirvonen T, Arnault N, et al. Consumption of black, green and herbal tea and iron status in French adults.. European journal of clinical nutrition. 2007. PMID 17299492. DOI 10.1038/sj.ejcn.1602634. (abstract)
Payne ER, Aceves-Martins M, Dubost J, et al. Effects of Tea (Camellia sinensis) or its Bioactive Compounds l-Theanine or l-Theanine plus Caffeine on Cognition, Sleep, and Mood in Healthy Participants: A Systematic Review and Meta-Analysis of Randomized Controlled Trials.. Nutrition reviews. 2025. PMID 40314930. DOI 10.1093/nutrit/nuaf054. (abstract)
Rothenberg DO, Zhou C, Zhang L. A Review on the Weight-Loss Effects of Oxidized Tea Polyphenols.. Molecules (Basel, Switzerland). 2018. PMID 29758009. DOI 10.3390/molecules23051176. (abstract)
Siener R, Hesse A. Effect of Black Tea Consumption on Urinary Risk Factors for Kidney Stone Formation.. Nutrients. 2021. PMID 34959987. DOI 10.3390/nu13124434. (abstract)
Wu KH, Lee JI, Lee YC, et al. Habitual tea consumption is associated with a lower prevalence of kidney stone disease in postmenopausal women.. PeerJ. 2024. PMID 39677960. DOI 10.7717/peerj.18639. (abstract)
Zhao Y, Asimi S, Wu K, et al. Black tea consumption and serum cholesterol concentration: Systematic review and meta-analysis of randomized controlled trials.. Clinical nutrition (Edinburgh, Scotland). 2015. PMID 24972454. DOI 10.1016/j.clnu.2014.06.003. (abstract)
n/a. EFSA: Caffeine, EFSA explains risk assessment (factsheet, 2015). n/a. 2015. (full-text)
n/a. IARC (WHO): Press release no. 244, IARC Monographs evaluate drinking coffee, mate, and very hot beverages (15 June 2016). n/a. 2016. (full-text)
n/a. FDA: Spilling the Beans: How Much Caffeine Is Too Much? (content current as of 28 Aug 2024). n/a. 2024. (full-text)
n/a. NHS (UK): Iron deficiency anaemia (page last reviewed 26 January 2024). n/a. 2024. (full-text)
n/a. NHS (UK): Foods to avoid in pregnancy (page last reviewed 15 June 2026). n/a. 2026. (full-text)
n/a. PubChem: Caffeine (CID 2519). n/a. 2026. (full-text)
n/a. PubChem: Theaflavin (CID 135403798). n/a. 2026. (full-text)
n/a. PubChem: Theaflavin 3,3'-digallate (CID 135536164). n/a. 2026. (full-text)
n/a. PubChem: L-Theanine (CID 439378). n/a. 2026. (full-text)
n/a. GBIF Backbone Taxonomy: Camellia sinensis (L.) Kuntze (usage key 3189635). n/a. 2026. (full-text)

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