Tea

Studies in people

• Concern

  Medicine absorption²

  Drinking green tea may lower how much of some medicines your body takes in.

• Benefit

  Type 2 diabetes risk³

  People who drank more tea were less likely to develop type 2 diabetes, though scientists say more research is needed.

• Benefit

  Dementia risk and memory⁴

  In adults, drinking tea was linked to lower dementia risk and slightly better cognitive function.

• Concern

  Liver injury from supplements⁵

  In people, green tea was linked to liver injury, often with jaundice, in 40 cases.

• Open question

  Memory and thinking⁶

  Some studies link green tea to lower dementia risk, but scientists do not yet know whether it truly helps.

• Concern

  Iron absorption from food⁷

  Tea can block iron absorption from meals, but eating meat or taking vitamin C at the same time may help.

• Benefit

  Body weight and belly fat⁸

  In people, green tea extract supplements lowered body weight, BMI and body fat, but not waist size.

• Benefit

  White blood cell activity⁹

  In healthy adults, 14 days of green tea extract increased white blood cell activity when blood was stimulated.

• No harm found

  Breast milk quality¹⁰

  In nursing mothers, drinking decaffeinated black tea did not raise the antioxidants or tea compounds in their breast milk.

• Benefit

  Disability in older adults¹¹

  In older Japanese adults, caffeine intake was linked to less disability, but green tea itself was not.

• Benefit

  Bone strength in women¹²

  In women, drinking tea for years was linked to stronger bones, but men saw no such link.

• Concern

  Breast density in women¹³

  In this study, decaffeinated tea was linked to denser breasts in some women, but scientists say larger studies are needed.

Animal and lab studies only

• Benefit

  Weight and blood sugar²³

  In animal studies, matcha tea lessened weight gain and improved blood sugar and fats on a high-fat diet.

Study type not stated

• Benefit

  Antioxidant levels in yoghurt¹⁷

  Adding Pu-erh tea to probiotic yoghurt greatly boosted its antioxidant power, though tasters liked it less than plain yoghurt.

• Benefit

  Heart and cancer protection¹⁸

  Tea is rich in antioxidants and may help protect against cancer, heart disease, kidney stones and cavities.

• Concern

  Liver health¹⁹

  Green tea extracts taken in large doses on an empty stomach were linked to liver problems, but brewed tea was not.

• Benefit

  Cancer prevention²⁰

  Green tea polyphenols like EGCG may help prevent cancer, but scientists do not yet know exactly how.

Found in some samples or products

These come from where it was grown, how it was processed or cooked, or what it was made into. They are not about the ingredient itself, so the signal does not count them.

• Pesticide exposure risk¹⁶

  In tea leaf samples, some pesticide levels were high enough to possibly matter for adult tea drinkers.

• Chemicals formed by roasting²¹

  Roasting Oolong tea, especially over charcoal, raises the PAH chemicals in the leaves, and hotter brewing releases more into your cup.

• Contaminants and infant risk²²

  Tea samples in Algeria held lead and aluminium, and infants could face health effects from drinking it regularly.

Single cases of misuse or overdose

One person or one incident, such as an accidental overdose or a mistake in a kitchen or factory. They are real, but a single case does not show what happens at normal amounts, so the signal does not count them.

• Brain white matter damage¹⁵

  A vegetarian woman who drank lots of tea developed brain problems after childbirth, but recovered with treatment.

How it’s made and used

• Toxin levels in drink¹⁴

  Some post-fermented tea in China held fumonisins, but amounts eaten stayed far below the daily limit.

The signal at the top counts the findings in people and in animal and lab studies. A concern in studies of people outranks animal and lab studies, and “No concerns” needs at least one finding in people. When most findings in people point one way, the page leans that way (“Mostly”), and every finding is still shown. Findings whose study type is not stated are shown but not counted. This page is a reference, not medical advice. It describes what regulators and published research say. Talk to a doctor or dietitian about your own diet.

Expert panels that weigh all the research. Shown for context: the signal at the top does not count them. IARC rates whether something can cause cancer at all, not how likely it is at the amounts in food.

• WHO cancer agency (IARC), 1990

  Not enough evidence to say whether it causes cancer in people (Group 3).