Need another excuse to drink that cup of coffee in the morning? Do you regularly reach for a cup of green tea when you need a mid-afternoon pick-me-up? You may be lowering your risk of stroke, if research published March 14 in Stroke: Journal of the American Heart Association holds true. Study findings suggest that the benefits of green tea and coffee consumption may include a reduction in risk of stroke by as much as 20%.

Study Findings At a Glance

Green tea and coffee consumption were both linked to reduced risk of stroke in a large, prospective multi-cohort study of Japanese adults.
People who drank at least four 6-ounce cups of green tea or coffee each day were 20 percent less likely to experience stroke
The study did not prove a causal relationship between drinking green tea and coffee and stroke prevention. It only shows an assocation.
Results suggest that coffee and green tea can be part of an overall health plan to reduce risk of stroke and other cardiovascular disease

What the Researchers Did

The large, prospective cohort study was conducted by a team of Japanese researchers led by Yoshihiro Kokubo, chief doctor in the department of preventive cardiology at the National Cerebral and Cardiovascular Center in Osaka, Japan.

For the study, Kokubo’s team assessed the dietary and green tea and coffee drinking habits of 82,369 adults in Japan. About half of the participants (47,400) were men, and half were women (53,538). All were between the ages of 45 and 72. Typically, a cup of tea or coffee in Japan is about six ounces.

The researchers followed participants for 13 years, tracking hospital medical records and death certificates. They collected information about stroke, heart disease, and causes of death. Then they analyzed the data, adjusting for age, sex and lifestyle factors like smoking, alcohol, weight, diet and exercise.

What the Researchers Found

When researchers compiled their results, they found that people who drank coffee and green tea daily were dramatically less likely to experience stroke. In general, the more green tea or coffee people drank, the lower their stroke risks. When they compared coffee and green tea drinkers to non-drinkers (or rare drinkers), they found that:

People who drank at least one cup of coffee daily had about a 20 percent lower risk of stroke
People who drank two to three cups of green tea daily had a 14 percent lower risk of stroke
People who drank at least four cups of green tea had a 20 percent lower risk of stroke
People one cup of coffee or two cups of green tea daily had a 32 percent lower risk of intracerebral hemorrhage – stroke that occurs when a blood vessel in the brain bursts, causing bleeding into brain tissue. Intracerebral hemorrhage is a type of hemorrhagic (“bleeding”) stroke.

“The regular action of drinking tea, coffee, largely benefits cardiovascular health because it partly keeps blood clots from forming,” said Kokubo.

Experts aren’t sure why green tea and coffee appear to lower stroke risk. Some scientists have proposed that a compound in green tea called catechins may play a role. Catechins are antioxidants and have anti-inflammatory properties, which help to prevent blood clots from forming.

The stroke-prevention benefits of coffee may stem from its known preventive effect on Type 2 diabetes. Coffee contains a chemical called chlorogenic acid, which lowers the chances of developing Type 2 diabetes. Type 2 diabetes is a major risk factor for stroke, so preventing that disease reduces stroke risk dramatically.

Why It’s Important

The study adds to a growing body of research that suggests caffeinated beverages, especially tea and coffee, may have protective effects on cardiovascular health.

Findings reported in 2008 suggested that men who drank more than five cups of coffee per day had a 44 percent lower risk of dying from heart disease, while women who drank four to five cups reduced their risk by 34 percent. Results from another study, also published in 2008, linked green tea consumption to better blood vessel function and lower risk of heart disease. And research reported in 2010 found a 45 percent lower risk of death from heart disease in people who drank three to six cups of green or black tea daily.

Still, not all studies have shown positive results. Many experts have expressed concern about the potentially harmful effects of caffeine on heart health and blood vessel function.

While other studies have focused on the effects of tea and coffee on the heart, Kokubo’s study was the first to specifically address stroke risk. “This is the first large-scale study to examine the combined effects of both green tea and coffee on stroke risks,” Kokubo said in a press release.

Stroke is a major health problem across the globe. Globally, according to the World Health Organization, nearly 15 million people have a stroke each year – and five million of them die. More than 795,000 people in the United States have a stroke each year. Stroke is the leading cause of disability and third leading cause of death in the United States, causing one out of every 19 deaths nationwide, according to the Centers for Disease Control and Prevention.

Kokubo’s findings on hemorrhagic stroke may be especially important. Although hemorrhagic strokes are less common than ischemic strokes, constituting about 13 percent of all strokes, they are more deadly. In developed countries, nearly one out of five people who experience hemorrhagic stroke die within 30 days of leaving the hospital, according to data from the Organisation for Economic Coopration and Development. In comparison, about one out of twenty ischemic strokes (stroke caused by a blood clot in the brain) lead to death within 30 days. So finding effective ways to prevent hemorrhagic stroke could have a huge impact on stroke mortality.

Study Limits

Researchers acknowledged several limitations to their findings. The study relied on self-reported data about dietary and other lifestyle habits. Dietary studies are especially prone to faulty memories. So it’s possible that study participants may have said they drank more tea and coffee than they actually did. “However, 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.

Initial study results showed increased risk of heart disease and stroke among coffee drinkers. But coffee drinkers were also more likely to be smokers. So when researchers controlled for smoking, they no longer found the positive association.

Conversely, green tea drinkers also exercised more. Since exercise is known to protect against stroke, higher rates of exercise among green tea drinkers could make green tea consumption appear more beneficial than it really is.

Generally, only caffeinated coffee is consumed in Japan, so the results do not necessarily apply to drinkers of decaffeinated coffee.

Tea and coffee are the most popular drinks in the world after water, suggesting that these results may apply in America and other countries. However, the study did not prove that drinking green tea or coffee causes fewer strokes. Although it did show a strong association between the two, it does not conclusively tease out whether specific compounds in tea or coffee protect against stroke or if tea or coffee drinkers may simply share another behavior that protects against stroke.

What It Means for You

“This is the first large-scale study to examine the combined effects of both green tea and coffee on stroke risks,” said Kokubo in a press 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.”

Adding green tea or coffee to your diet may be helpful, but they can’t cover up for multiple dietary or lifestyle “sins.” In addition to drinking that cuppa, stroke prevention steps include following American Heart Association guidelines for regular exercise, weight control, and heart-healthy dietary patterns that include lots of fruits, vegetables, lean meats, fish, and monounsaturated fats, and few sweets. Get your blood pressure and cholesterol levels checked regularly, and control them if they are high.

In sum, this study adds to growing evidence that coffee and tea, although no panacea, appear to have a place in a heart- and brain-healthy diet.