Study: Green tea, coffee may protect against stroke

Green tea and coffee may help lower stroke risk, especially when each is a regular part of a diet, according to a Japanese study.

“This is the first large-scale study to examine the combined effects of both green tea and coffee on stroke risks,” Yoshihiro Kokubo, MD, PhD, FAHA, FACC, FESC, the study’s lead author out of the National Cerebral and Cardiovascular Center in Japan, said in a news release. “You may make a small but positive lifestyle change to help lower the risk of stroke by adding daily green tea to your diet.”

Researchers asked 83,269 Japanese adults about their green tea and coffee drinking habits, following them for an average of 13 years. As reported March 14 on the website of Stroke, an American Heart Association journal, they found that the more green tea or coffee people drink, the lower their stroke risk:

• People who drank at least one cup of coffee daily had about a 20% lower risk of stroke compared with people who rarely drank it.

• People who drank two to three cups of green tea daily had a 14% lower risk of stroke, and those who had at least four cups had a 20% lower risk, compared with those who rarely drank it.

• People who drank at least one cup of coffee or two cups of green tea daily had a 32% lower risk of intracerebral hemorrhage, compared with those who rarely drank either beverage.

Participants in the study were ages 45 to 74, almost evenly divided in gender and free of cancer and cardiovascular disease.

During the 13-years of follow-up, researchers reviewed participants’ hospital medical records and death certificates, collecting data about heart disease, stroke and causes of death. They adjusted their findings to account for age, sex and lifestyle factors such as smoking, alcohol, weight, diet and exercise. Green tea drinkers in the study were more likely to exercise compared with non-drinkers.

Previous limited research has shown green tea’s link to lower death risk from heart disease, but has only touched on its association with lower stroke risk. Other studies have shown inconsistent connections between coffee and stroke risk.

Initial study results showed that drinking more than two cups of coffee daily was linked to increasing coronary heart disease rates in age- and sex-adjusted analysis. But the researchers said they did not find the association after factoring in the effects of cigarette smoking, thus underscoring smoking’s negative health impact on heart and stroke health.

A typical cup of coffee or tea in Japan was approximately 6 ounces. “Our self-reported data may be reasonably accurate, because nationwide annual health screenings produced similar results, and our validation study showed relatively high validity,” Kokubo said. “The regular action of drinking tea [and] coffee largely benefits cardiovascular health because it partly keeps blood clots from forming.”

Tea and coffee are the most popular drinks in the world after water, suggesting these results may apply in America and other countries, the researchers said.

How green tea affects stroke risk is unclear, the researchers said. A compound group known as catechins may provide some protection. Catechins have antioxidant and anti-inflammatory effects, increasing plasma antioxidant capacity and anti-thrombogenic effects.

Chemicals in coffee include chlorogenic acid, thus cutting stroke risks by lowering the chances of developing type 2 diabetes.

Further research could clarify how the interaction between coffee and green tea might help further lower stroke risks, Kokubo said.

The study abstract is available at

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