Tea is the most widely drunk beverage in the world after water, and every true tea, whether white, green, oolong or black, comes from the same plant, Camellia sinensis. Its compounds have been studied for decades for possible effects on the heart and on cancer. Some findings hold up in people, many don't yet, and a few come with real cautions. Here is where the evidence stands.
What's in your cup
Tea leaves are rich in polyphenols, plant compounds that act as antioxidants in the laboratory. The best known are the catechins, and in particular EGCG (epigallocatechin gallate), which is the most abundant catechin in green tea.
Processing changes the mix. White tea, made from young buds and leaves with little handling, and green tea, which is heated soon after picking, keep most of their catechins. Oolong is partly oxidized and black tea fully oxidized, which turns many catechins into theaflavins and thearubigins, the compounds behind black tea's color and body. All four contain caffeine and L-theanine, an amino acid linked to tea's calm-but-alert reputation.
Herbal "teas" such as chamomile, rooibos or peppermint come from other plants entirely, so the research on this page doesn't apply to them.
Tea and heart health
Large observational studies, which follow big groups of people for years, have linked regular tea drinking with a somewhat lower risk of heart disease and stroke. According to the US National Center for Complementary and Integrative Health (NCCIH), the link between green tea and lower coronary heart disease risk has shown up in studies of Asian populations but not in Western ones.
Clinical trials, where people are assigned to drink tea or not, are smaller and shorter. In those trials green tea, mostly given as extract supplements rather than brewed tea, lowered total and LDL ("bad") cholesterol by a small amount. Trials of black tea suggest modest improvements in how well blood vessels relax.
The catch is that associations are not proof. People who drink tea every day may also differ in what they eat, how much they smoke or exercise, and how much they earn, and studies can't fully account for all of that. Tea may be a modest plus for the heart, but it isn't a treatment, and it doesn't replace the things known to make a difference, such as not smoking, staying active and managing blood pressure.
Tea and cancer
In test tubes and animal studies, EGCG and other tea compounds slow the growth of cancer cells, interfere with the blood supply tumors need, and protect cells from damage. Those results explain why researchers keep studying tea.
The human evidence is much less clear. Studies of tea drinkers and cancer risk have produced inconsistent results, and NCCIH says no firm conclusion can be drawn about whether green tea helps prevent cancer. Lab doses of EGCG are also often far higher than anything a cup of tea delivers.
One link is better established, and it is about temperature rather than tea. The International Agency for Research on Cancer classifies drinking very hot beverages, above about 149°F (65°C), as a probable cause of esophageal cancer. Letting tea cool for a few minutes before drinking takes care of it.
What we know, and what we don't
Reasonably established: brewed tea is a safe everyday drink for most adults, and very hot drinks raise the risk of esophageal cancer.
Possible but uncertain: a modestly lower risk of heart disease among regular tea drinkers, and small improvements in cholesterol.
Seen mainly in the lab: effects of tea compounds on cancer cells, tumors and the immune system.
Cautions
Caffeine. The FDA puts up to 400 mg of caffeine a day as an amount not generally linked to negative effects in most healthy adults. A 12-ounce serving of black tea has about 70 mg and green tea just under 40 mg. People who are pregnant, trying to become pregnant or breastfeeding should ask their health care provider how much caffeine is right for them.
Green tea extracts. Concentrated green tea supplements, in pills or capsules, have been linked to rare cases of liver injury. That has not been seen with tea as a drink.
Medicines. Large amounts of green tea can lower blood levels of the beta-blocker nadolol, and green tea extract can affect some other drugs. If you take medication and plan to drink a lot of green tea or take a supplement, check with your doctor or pharmacist.
Iron. Tea drunk with meals can reduce how much iron the body absorbs from plant foods. For anyone low in iron, drinking tea between meals rather than with them is a simple fix.
What goes in it. Sugar, syrups and sweetened bottled teas add calories that can outweigh whatever the tea itself offers.
Enjoying tea
The best reason to drink tea is that you like it: the ritual, the flavor, the warmth of the cup. Brew it the way you enjoy it, let it cool a little, and treat any health effects as a possible bonus rather than the point. Learn more about the different types and how to brew them in our guide to tea.
Sources
- Green tea (National Center for Complementary and Integrative Health)
- Spilling the beans: how much caffeine is too much? (US Food and Drug Administration)
- Health-promoting effects of black tea: a narrative review of clinical trials (International Journal of Food Science, 2025)
- Drinking coffee, mate, and very hot beverages, IARC Monographs volume 116 (International Agency for Research on Cancer, 2016)
Last reviewed November 2026. This article is general information, not medical advice.