Conducted Studies that Make You Rethink Tea

I recently reviewed several medical studies about tea. Together, they offer useful insights into how tea drinking may relate to longevity, heart health, mood, and blood pressure.

The wording matters. Most long-term tea studies are observational. They can find associations, but they cannot prove that tea caused the results.

Medical Tea Studies at a Glance

Can Tea Help You Live Longer?

Several studies have connected regular tea drinking with a lower risk of death. However, this does not prove that tea extends life.

One study examined more than 9,000 Chinese adults aged 80 and older. Consistent tea drinkers had a lower mortality rate than people who rarely or never drank tea. The results varied based on when participants developed or maintained the habit. Read the study. (1)

Another study followed more than 100,000 Chinese adults. Researchers compared habitual tea drinkers with people who rarely drank tea.

Habitual tea drinkers consumed tea at least three times per week. They had a 20% lower risk of heart disease and stroke during the study period. They also had a 22% lower risk of death from those conditions and a 15% lower risk of death from any cause.

At age 50, habitual tea drinkers were also projected to live about 1.26 years longer without cardiovascular disease. These figures describe statistical associations rather than guaranteed benefits for each person. Review the study summary. (2)

UK Tea Study

Researchers have also studied tea drinking outside China. One large study included nearly 500,000 participants in the United Kingdom.

The researchers followed participants for a median of about 11 years. People who drank two or more cups of tea each day had a moderately lower risk of death than nondrinkers.

Black tea accounted for most of the tea consumed. The association remained present regardless of whether participants added milk or sugar. It also remained across different preferred tea temperatures and genetic differences in caffeine metabolism. Read the UK Biobank study. (3)

This does not mean that additions never matter. Large amounts of sugar add calories and can reduce the nutritional value of a drink. However, the study did not show that adding milk removed tea’s association with lower mortality.

Can Tea Improve Your Mood?

A 2018 study examined caffeine, green tea, and other dietary factors among Korean adults. It found an association between green tea consumption and a lower prevalence of depression.

However, this type of study cannot show that green tea or caffeine prevents depression. Diet, income, exercise, sleep, social habits, and existing health can all influence the results. Read the study. (4)

Caffeine can temporarily improve alertness and energy. A warm cup of tea may also provide comfort as part of a calming routine.

However, tea does not treat clinical depression. Excess caffeine can worsen anxiety, restlessness, and sleep problems in sensitive people.

Anyone experiencing lasting sadness, hopelessness, loss of interest, or thoughts of self-harm should seek help from a qualified healthcare professional.

Caffeine in Tea

Tea contains less caffeine than many servings of coffee or energy drinks. However, the amount varies widely.

Leaf quantity, tea type, water temperature, and brewing time can change these numbers.

For most healthy adults, the U.S. Food and Drug Administration considers up to 400 mg of caffeine per day an amount not generally linked with harmful effects. Pregnancy guidance commonly limits daily caffeine to 200 mg. Harvard’s caffeine overview explains these amounts. (5)

The earlier estimate of 50–300 mg as a universal “moderate” range does not serve as an official safety limit. Personal tolerance also matters.

Some people develop anxiety, a rapid heartbeat, stomach discomfort, or sleep problems at much lower doses. Children, adolescents, pregnant people, and people taking certain medications require more caution.

Could Fermented Tea Be Beneficial?

Kombucha is a fermented drink made from tea, sugar, bacteria, and yeast. It contains organic acids and other compounds created during fermentation.

Despite its long history and modern popularity, research has not confirmed many of its advertised health benefits. A 2019 systematic review found very little human clinical evidence. Read the systematic review. (6)

Research on fermented foods in general does not prove that kombucha provides the same effects. Each fermented product contains different organisms and compounds. Review the research on fermented foods. (7)

Commercial kombucha can also contain added sugar, caffeine, and a small amount of alcohol. Homemade versions may become contaminated if producers do not control sanitation and acidity.

Pregnant people and anyone with a weakened immune system should ask a healthcare professional before drinking unpasteurized kombucha.

Tea and Blood Pressure

A 2020 meta-analysis reviewed more than 1,000 records but included only five eligible trials. Together, those trials involved 408 participants.

The analysis found that regular tea consumption produced small reductions in systolic and diastolic blood pressure. Longer interventions showed stronger results. Green tea appeared to have a greater effect than black tea in this analysis. Read the meta-analysis. (8)

The small number of studies and participants limits the strength of the conclusion. Tea should not replace blood pressure medication or medical care.

People with high blood pressure should monitor their caffeine response. Caffeine can temporarily raise blood pressure, especially in people who do not consume it regularly.

Tea and Heart Disease

A Dutch study followed more than 37,000 adults for about 13 years. Moderate tea consumption was associated with a lower risk of death from coronary heart disease.

Participants who drank more than six cups per day also had a lower observed risk of coronary heart disease. However, the study did not find a clear relationship between tea intake and stroke. Read the Dutch cohort study. (9)

This was an observational study. It could not prove that tea caused the lower risk.

Tea can still fit into a heart-healthy lifestyle, especially when it replaces sugary drinks. Exercise, sleep, diet, tobacco avoidance, and medical care remain much more important than any single drink.

The Risk of Drinking Very Hot Tea

The risk linked with hot tea comes from temperature rather than the tea leaves.

A large study in Iran followed more than 50,000 adults. Drinking tea at 60°C, or 140°F, and above was associated with a higher risk of esophageal squamous cell carcinoma.

The strongest association appeared among people who drank at least 700 milliliters of tea per day at these temperatures. Read the hot-tea study. (10)

Very hot liquids may repeatedly injure the lining of the esophagus. The same concern can apply to coffee, hot chocolate, and other hot drinks.

Brewing temperature and drinking temperature are different. You can prepare black tea with near-boiling water and then let it cool before drinking.

Avoid drinking any beverage while it feels painfully hot. Waiting several minutes provides a simple way to reduce the risk.

Green Tea Extract and Liver Injury

Brewed green tea is generally safe for most adults. Concentrated green tea extracts create a different risk.

Case reports have linked some green tea extract supplements with liver injury. In severe cases, patients have required hospitalization or a liver transplant.

The possible cause involves concentrated catechins, particularly epigallocatechin gallate, or EGCG. Risk may increase when people take high doses or consume the supplements without food.

The problem is not simply that the compounds are “synthetic.” Many supplements contain concentrated compounds extracted from real tea leaves.

A clinical review documented cases of liver injury associated with green tea extract products. Read the review. (11)

Stop using a supplement and seek medical care if you develop yellow skin, dark urine, severe fatigue, abdominal pain, nausea, or unusual itching.

People with liver disease should speak with a healthcare professional before taking green tea extract. The risk from drinking normally brewed green tea appears much lower.

Summary of Medical Tea Studies

Research links regular tea drinking with several positive health outcomes. These include lower observed rates of mortality, cardiovascular disease, and high blood pressure.

However, most of these findings show associations. Tea drinkers may also have different diets, exercise habits, incomes, healthcare access, and social routines.

Tea is not a cure or a substitute for medical treatment. It can still serve as an enjoyable part of a balanced lifestyle.

For safer tea consumption:

• Limit added sugar.
• Monitor your total caffeine intake.
• Let very hot tea cool before drinking it.
• Use caution with green tea extract supplements.
• Do not use tea to replace prescribed medication or professional care.

Tea has remained popular for thousands of years because of its flavor, variety, and cultural value. Its possible health benefits provide another reason to enjoy it, but the scientific evidence calls for balance rather than exaggerated promises.

References

1. Tea consumption and mortality among the oldest-old Chinese
2. Habitual tea drinking and cardiovascular health
3. Tea consumption and mortality in the UK Biobank
4. Green tea, caffeine, and depression among Korean adults
5. Harvard Nutrition Source: Caffeine
6. Kombucha systematic review
7. Review of fermented foods and health
8. Tea consumption and blood pressure meta-analysis
9. Tea, coffee, and cardiovascular disease in a Dutch cohort
10. Hot tea consumption and esophageal cancer risk
11. Green tea extract and liver injury