Two or more cups a day boosts protection for nonsmokers, study finds
The finding stems from the tracking of both coffee habits and stroke occurrence among tens of thousands of American women across nearly a quarter century. And it adds to earlier indications that coffee might also offer some protection against diabetes, while not raising the risk for heart trouble.
However, the current evidence also includes a cautionary note for smokers: Their habit seems to wipe out whatever protection long-term coffee drinking might otherwise confer.
"Many people have been very concerned that coffee might actually be a risk factor for stroke, that it might, in fact, increase the risk of stroke," said the study's co-author, Rob M. van Dam, an assistant professor at Harvard Medical School and Harvard School of Public Health, in Boston. "But here we saw that it might end up being beneficial rather than detrimental."
The findings were released Monday for the March 3 issue of Circulation.
To explore possible links between coffee drinking and stroke risk among women, the authors analyzed data on more than 83,000 women, who averaged about 55 years old and had participated in the Nurses' Health Study between 1980 and 2004. At the start of the study, none of the women had a history of stroke, heart disease, diabetes or cancer.
Based on the women's answers on seven food-habit surveys administered during the study, the researchers found that 84 percent of the women consumed at least some caffeinated coffee. As well, half said they drank decaffeinated coffee, 78 percent drank tea and 54 percent drank caffeinated sodas.
During the study's 24-year span, nearly 2,300 strokes occurred. More than half were ischemic strokes, which follow blood vessel blockage.
Coffee drinking was not linked to either the lowering or the raising of stroke risk among women who developed high blood pressure, diabetes or high cholesterol.
But after considering factors such as cigarette and alcohol consumption, van Dam and his colleagues found that healthy women who consumed two to three cups of caffeinated coffee a day had, on average, a 19 percent lower risk for any kind of stroke than did women who drank less than one cup a month. Drinking four or more cups a day lowered risk by 20 percent.
Women who drank five to seven cups of coffee a week were 12 percent less likely to have a stroke than were those who downed just one cup a month, the study found.
The team then zeroed in on the impact tobacco might have on the coffee-stroke link, noting that coffee drinkers are often also smokers.
What they found was striking: Among women who never smoked or had smoked but quit, drinking four or more cups of coffee a day conferred a 43 percent reduced risk for all types of stroke. However, among women with similar coffee habits who also smoked, stroke risk fell by just 3 percent.
It remains unclear what specific aspect of coffee plays the principal role in stroke risk reduction. However, the researchers noted that caffeinated tea and soft drinks carried no similar benefit -- implying that some other component in coffee, apart from caffeine, might provide the protective effect.
Whatever the case, the study authors pointed out that certain conditions -- such as insomnia, anxiety, high blood pressure and cardiac complications -- can be negatively affected by coffee drinking.
They further cautioned that the current findings need confirmation with continued research.
"This is quite an early finding," van Dam said. "And previous studies have been quite small. But the data we do have is very convincing in the sense that we feel comfortable that we definitely found no association between high coffee consumption and a higher stroke risk. So women can continue to enjoy their coffee and focus on other things to reduce stroke risk, such as engaging in more physical activity, reducing salt intake and stopping smoking."
Dr. Anthony Comerota, director of the Jobst Vascular Center at Toledo Hospital in Ohio, described the degree of benefit as "somewhat surprising."
"But what is not surprising," he said, "is the deleterious impact of cigarette smoking, which we know is the most potent risk factor -- perhaps other than diabetes -- for heart attack and stroke and general cardiovascular-related risk among both men and women."
Comerota suggested that future research should explore physical activity patterns among coffee drinkers and nondrinkers. "There may be behavior patterns which link increased physical activity with coffee drinking," he said, "and we know the more physical activity one has, the better cardiovascular risk reduction that person enjoys."
Drinking coffee appears to lower the risk for stroke among women, with more consumption translating into more protection, Spanish and American researchers suggest.
Another large study appearing in the same issue of Circulation offered insight into the impact of diet on stroke risk. It noted that American women who closely follow a traditional Mediterranean diet (high in monounsaturated fats, plant-based proteins, whole grains and fish) have a much lower risk for both heart disease and stroke.
As with van Dam's research, this study -- led by Teresa T. Fung of Simmons College and the Harvard School of Public Health in Boston -- was also based on analysis of participants in the Nurses' Health Study, nearly 75,000 of whom were tracked for two decades to see how their dietary habits stacked up against their incidence of both stroke and heart attack.
For more on diet and heart health, visit American Heart Association.