However, a new survey of hundreds of thousands of adults failed to show cause and effect.

Written by Hannah Seo | Published on November 17, 2021 at 4:00 PM

A new study shows that drinking a moderate amount of coffee or tea may reduce the risk of stroke or dementia. 

Researchers surveyed 365,682 adults between the ages of 50 and 74 and asked them how much tea or coffee they drink each day. The team then tracked the health results of each participant for more than a decade. At the end of the study period, according to hospital records, there were 5,079 cases of dementia and 10,053 cases of stroke. Those who drink two to three cups of coffee or three to five cups of tea a day, or four to six cups of coffee and tea at the same time are least likely to suffer from stroke or dementia. Compared with abstinents, people who drink coffee and tea have a 28% lower risk of dementia and a 32% lower risk of stroke. The new study was published in PLOS Medicine on Tuesday. 

"Our research results show that drinking coffee and tea in moderation separately or at the same time is associated with a lower risk of stroke and dementia," the author wrote in the paper.

Despite the bold statistics, the new research has not established any causality. "We can't attribute it to cause and effect and say that'drinking more coffee or tea is good for the brain,'" Lee H. Schwamm, chairman of the American Stroke Association Advisory Board and chairman of the Vascular Neurology at Massachusetts General Hospital, told CNN in an email "We can only say that in this study, people who reported drinking coffee/tea in moderation were less likely to have a stroke or dementia during the 10-year follow-up."

This new study has many additional limitations, which the authors acknowledge in their paper. For example, it is important to note that the team only used self-reported coffee and tea consumption data at the beginning of the study. If people's coffee drinking habits have fundamentally changed during the study period, these data will not be collected.

In addition, self-reported alcohol consumption can be a tricky indicator because people may remember how many cups they drank, and the definition of "cup" may be different. The participants are also very homogeneous, mainly white, from the "socio-economically impoverished areas" of the United Kingdom.

[Related: The ultimate guide to making cafe-style coffee at home]

A large number of studies have shown that a small to moderate amount of caffeine intake is good for health. Caffeine is the psychostimulant in these drinks and has previously been associated with lowering the risk of dementia and Alzheimer's disease. Caffeine intake is also associated with reducing the risk of heart failure and Parkinson's disease. Nevertheless, the health value of coffee is still controversial, especially at higher consumption levels.

Kevin McConway, a statistician at the Open University of England, told The Guardian that this study showed that the association between stroke and dementia risk and coffee/tea drinking only works to a certain extent—“a certain level of consumption Later, the risk began to increase again, until it became higher than the risk of people who did not drink alcohol.... Once you drink seven or eight cups of coffee a day, the risk of stroke is greater than that of people who do not drink coffee, than those who drink two or three cups a day. People are much taller.” Although caffeine is useful for morning buzz, beware of headlines that are too noisy because it is good for health.

Hannah is a freelance science journalist, podcast writer, and poet based in Brooklyn. In addition to popular science, her work can also be found in magazines such as Wired, Scientific American, Walrus, and Environmental Health News.

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