Drinking black tea—at least two cups a day—may help people live a longer, healthier life, according to new research from the National Institutes of Health.
The findings, published Monday in the Annals of Internal Medicine, found that black tea drinkers had a “modestly” lower risk of death from all causes, as well as death from cardiovascular disease, ischemic heart disease, and stroke.
While past evidence has linked tea consumption with greater longevity, those studies predominantly evaluated green tea, typically in Asian populations. Research on black tea—which is the most common type of tea consumed in the United Kingdom—had previously been limited with mixed findings.
The new research, however, suggests that the health benefits of black tea are similar to those of green tea, and that even higher levels of black tea consumption can be part of a healthy diet.
Two Cups of Black Tea Each Day Linked to Lower Risk of Death
For the study, researchers from the National Cancer Institute evaluated the health data from 498,043 people in the U.K. between the ages of 40 and 69, sourced by the UK Biobank, a large-scale biomedical database.
The participants completed a baseline questionnaire that included questions about their tea-drinking and lifestyle habits, and researchers compared those self-reported habits to mortality rates from all causes.
The participants were followed for about 11 years, and researchers determined that people who drank at least two cups of tea per day had a 9%–13% lower risk of death from all causes, compared to people who did not drink tea at all.
People who drank more tea were also found to have lower rates of death from cardiovascular disease, ischemic heart disease, and stroke.
The findings held true regardless of how people enjoyed their tea—hot or cold, with or without milk or sugar—and how quickly or slowly they were able to metabolize the caffeine.
The health benefits appeared to cap off around two cups of tea a day. Although more tea wasn't necessarily harmful, there weren't any added health benefits.
Health Benefits of Green Tea
Health Benefits Associated With Black Tea
Black tea contains high levels of polyphenols and flavonoids, which are known to reduce oxidative stress and inflammation, according to Dana Hunnes, PhD, MPH, RD, senior clinical dietitian at UCLA Medical Center, and assistant professor at UCLA Fielding School of Public Health, who was not involved in the new research.
“It is likely that what this study was seeing may be related to the effect of these phytonutrients and compounds in tea that reduce oxidative stress and inflammation, and therefore lower the risk of all-cause mortality,” Hunnes, who is also the author of Recipe for Survival, told Health.
Both inflammation and oxidative stress damage our cells and may eventually lead to cancer, according to Benjamin Hirsh, MD, director of preventive cardiology at Northwell Health’s Sandra Atlas Bass Heart Hospital, who was not involved in the new study.
Hunnes added that inflammation has also been found to be a contributing factor for many other health conditions, too, like heart disease, stroke, and diabetes.
“Inflammation is affected significantly by what we eat, what we drink, and whatever else we ingest,” said Hunnes, “which is why so many conditions are now considered ‘nutrition-related chronic disease.”
But in consuming foods and beverages that are rich in phytonutrients—compounds produced by plants—people can give their bodies a nutritious boost by enhancing immunity and repairing and protecting against cellular damage.
"Similar to fruits and vegetables, polyphenols and flavonoids are helpful in reducing inflammation […] and promoting cellular protection from damage," said Dr. Hirsh.
Consuming flavonoids and polyphenols specifically—the types of phytonutrients found in black tea—can help improve blood vessel function, lower bad cholesterol, and manage insulin sensitivity, among other things, according to Guy L. Mintz, MD, director of cardiovascular health and lipidology at Northwell Health’s Sandra Atlas Bass Heart Hospital, who was not involved in the new research.
Black Tea Consumption May Not Be the Only Factor
Although researchers concluded that black tea—even in larger amounts—can be part of a healthy diet, it's important to point out that more research will be needed to see how drinking black tea may affect other populations, since participants in the new research were predominantly white.
“Although the associations were assessed comprehensively and carefully, these results need to be replicated in future studies and extended in other diverse populations,” corresponding author Maki Inoue-Choi, PhD, staff scientist in the division of cancer epidemiology and genetics with the National Cancer Institute, said in a media briefing.
Further research on how lifestyle and genetic factors affect the benefits of tea consumption will also be necessary—particularly because the study was observational, said Hunnes.
"Is it that they're drinking tea and not sugar-sweetened beverages? Is it that the tea itself is a wondrous beverage with all of its phytonutrients, polyphenols, and flavonoids? Is it a combination of all of the above?" Hunnes said, adding that we just don't know those answers yet.
And while the findings suggest tea can be part of a healthful diet, this doesn't necessarily mean everybody needs to commit to drinking multiple cups of tea a day, according to the researchers.
If you do add tea to your diet, listen to your body. Tea contains a lot of caffeine and some people may be sensitive to its stimulating effects. It’s also a diuretic and too much may lead to dehydration, said Dr. Mintz.
But those who enjoy a couple cups of tea a day should probably stick with it for the potential health benefits. "If you have no problem with caffeine, drink to your heart's content," said Hunnes, "but you won't really see much benefit beyond just drinking two cups per day."