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Sept. 19, 2022 — Several recent studies have suggested that drinking several cups of tea per day could lower the risk of diabetes, heart disease, and stroke.
The latest study indicates that drinking four cups of black, green, or oolong tea per day can lower the risk of developing type 2 diabetes by 17% over a decade. The research will be presented next week at the European Association for the Study of Diabetes annual conference.
“Our results are exciting because they suggest that people can do something as simple as drinking four cups of tea a day to potentially lessen their risk of developing type 2 diabetes,” Xiaying Li, a researcher at Wuhan University of Science and Technology, told NBC News.
Li and colleagues reviewed 19 studies, which included more than 1 million adults across 8 countries. They found that the benefits of drinking tea went up as someone drank more cups. For one to three cups per day, for instance, the risk of type 2 diabetes dropped by 4%. The percentages increased from there.
In another study published last month, researchers found that drinking two or more cups of black tea per day lowered the overall risk of death by 9% to 13% among 498,000 people in the U.K. during a 14-year period, as compared with those who drank no tea. The study also found a link between drinking multiple cups of tea per day and a lower risk of heart disease and stroke.
“We think our findings will be very reassuring to people who are already drinking tea,” Maki Inoue-Choi, PhD, a staff scientist at the National Cancer Institute, told NBC News.
Even among those who drank more than 10 cups of tea per day, “we didn’t see any negative effects on mortality risk,” she said.
The health benefits could stem from the polyphenols in tea, which are natural compounds in plants that provide antioxidants and may decrease inflammation, Inoue-Choi noted. Reducing inflammation can lower the risk of developing health conditions such as heart disease.
In green tea, the dominant polyphenols are called catechins, which can protect cells from damage, NBC News reported. When green tea leaves are fermented to make black tea, the catechins convert to theaflavins, which provide another form of antioxidants.
Inoue-Choi said she and colleagues found that adding milk or sugar to tea didn’t reduce the health benefits. But she noted that the participants tended to use those ingredients sparingly.
“The sweetened tea from the store has a lot more sugar,” she said. “We should still follow the dietary guidelines to avoid too much sugar and too much saturated fat.”
Other studies have found that drinking tea may provide other health benefits as well, such as reducing the risk of lung, ovarian, prostate, or colorectal cancer. But the results have been mixed. Other studies have found that drinking several cups of black tea per day can increase the risk of breast cancer, and one study found that drinking extremely hot tea can increase the risk of esophageal cancer.
“Findings for cancer have been more mixed,” Inoue-Choi said. ‘There have been more consistent results for [reduced risks of] heart disease or stroke.”
For now, she said, drinking tea appears beneficial, but scientists wouldn’t likely tell people to change their behavior or give recommendations about the ideal amount of tea to drink.
“We wouldn’t recommend people change their tea intake solely based on this single study,” Inoue-Choi said.
NBC News: “Drinking tea may lower the risk of diabetes, heart disease and death, mounting research shows.”
European Association for the Study of Diabetes: “EASD 2022.”
Annals of Internal Medicine: “Tea Consumption and All-Cause and Cause-Specific Mortality in the UK Biobank.”
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