The study looked at the green tea and coffee drinking habits of more than 82,000 Japanese adults, ages 45 to 74, for an average of 13 years. Researchers found that the more green tea or coffee people drink, the lower their risk of having a stroke.
Tea and coffee are the most popular drinks in the world after water, suggesting that these results may apply in other countries, too.
Previous limited research has shown green tea's link to lower death risks from heart disease, but it has only touched on the association with lower stroke risks. Other studies have shown inconsistent connections between coffee and stroke risks.
The new study found:
- People who drank at least 1 cup of coffee daily had about a 20% lower risk of stroke compared to those who rarely drank it.
- People who drank 2 to 3 cups of green tea daily had a 14% lower risk of stroke, and those who had at least 4 cups had a 20% lower risk, compared to those who rarely drank it.
- People who drank at least 1 cup of coffee or 2 cups of green tea daily had a 32% lower risk of intracerebral hemorrhage, compared to those who rarely drank either beverage. Intracerebral hemorrhage happens when a blood vessel bursts and bleeds inside the brain. About 13% of strokes are due to this condition.
Researchers adjusted their findings to account for age, sex, and lifestyle factors like smoking, alcohol, weight, diet, and exercise. Green tea drinkers in the study were more likely to exercise than non-drinkers.
What's in a Cup?
Dale Webb, DPhil, director of research and information at the U.K.'s Stroke Association, says in an email: "We welcome this study, which suggests that the benefits of antioxidants in coffee and green tea may offset the potential harm from caffeine. The results demonstrate higher consumption of green tea and coffee might reduce the risks for stroke, especially for intracerebral haemorrhage.
"We would like to see further research to understand the underlying biological mechanisms for these findings."
It's unclear how green tea affects stroke risks. A compound group known as catechins may provide some protection, as they have an antioxidant anti-inflammatory effect.
Some chemicals in coffee include chlorogenic acid, which is thought to cut stroke risks by lowering the chances of developing type 2 diabetes.