Women who drink more than one cup of coffee a day might have a 22 to 25 percent lower risk of stroke, according to a new study announced Thursday (March 10) by the American Heart Association.
The study, which is published in the association's journal "Stroke," looked at 34,670 Swedish women ages 49 to 83 who were followed for an average 10.4 years. Women who drank one to two, three to four, or five or more cups of coffee per day had similar benefits compared with those who reported daily intake of less than a cup, researchers from the National Institute of Environmental Medicine, Karolinska Institute in Stockholm, Sweden, said.
Women who drank little or no coffee had an increased risk of stroke, researchers found.
Scientists have theorized that coffee could have either beneficial or harmful effects on the cardiovascular system, but earlier studies have been inconclusive. Only one previous study examined the association between coffee consumption and stroke incidence in healthy women, but it was also inconclusive, according to the American Heart Association.
Coffee is one of the most widely consumed beverages in the world, so even small health effects of substances in coffee may have large public-health consequences, Susanna Larsson, Ph.D., the study's lead author and a researcher in the Division of Nutritional Epidemiology, said.
"Some women have avoided consuming coffee because they have thought it is unhealthy. In fact, increasing evidence indicates that moderate coffee consumption may decrease the risk of some diseases such as diabetes, liver cancer and possibly stroke," she said.
The differences were unchanged by smoking status, body-mass index, and history of diabetes, hypertension or alcohol consumption, indicating that coffee's effects are not influenced by those cardiovascular risk factors.
The women participated in the Swedish Mammography Cohort, a long-running epidemiological study investigating the association of diet, lifestyle and disease development. All participants were free of cardiovascular disease and cancer at the study's beginning in 1997.
Larsson's team collected data on cases of first stroke among the women that occurred between Jan. 1, 1998, and Dec. 31, 2008. The researchers documented 1,680 strokes: 1,310 cerebral infarctions/ischemic strokes (caused by blockages), 154 intracerebral hemorrhages (caused by bleeding inside the brain), 79 subarachnoid hemorrhages (caused by bleeding on the surface of the brain) and 137 unspecified strokes.
After adjustment for other risk factors, the coffee consumption was associated with a statistically significant lower risk of total stroke, stroke caused by blockages and bleeding on the brain's surface, Larsson said. Strokes cased by blockages are generally most strongly associated with dietary factors.
The study made no distinction between regular and decaffeinated coffee, but decaffeinated-coffee consumption in Sweden is low, Larsson said.
Potential ways that coffee drinking might reduce the risk of stroke include weakening inflammation in arteries that is associated with heart disease, reducing oxidative stress caused by toxins and "free radicals" that are part of natural metabolism and lowering the body's need for insulin (insulin sensitivity), she said.
Larsson previously published a study in 2008 for the American Heart Association showing that coffee and tea consumption could potentially reduce the risk of stroke in male smokers.
More studies on coffee consumption and stroke are needed before firm conclusions can be reached, Larsson said.