July 15, 2010 -- Just one drink -- whether beer, wine, or hard liquor -- may double your risk of stroke in the hour after your cocktail hour, according to a new study in Stroke. A few hours later, however, your risk seems to return to its previous level.
Numerous studies have shown that moderate alcohol consumption-- no more than two drinks per day for men and one drink per day for women -- may provide some important health benefits including lower risk for heart disease and stroke. To keep moderate drinking in perspective, a drink is defined as one 12-ounce beer, 4 ounces of wine, 1.5 ounces of 80-proof spirits, or 1 ounce of 100-proof spirits.
"There is a small transient increase in risk of stroke after one drink, but it goes away over 24 hours," says study researcher Murray A. Mittleman, MD, DrPH, director of the Cardiovascular Epidemiology Research Unit at Beth Israel Deaconess Medical Center in the Harvard Medical School in Boston.
Exactly why this occurs is not fully understood, but alcohol may increase blood pressure levels or affect the blood's ability to clot, he tells WebMD. High blood pressure and abnormal blood clotting can increase stroke risk.
"These changes occur rapidly and may be responsible for the transient increase in stroke risk," Mittleman says. "Many of these factors return to baseline in a number of hours, and there are some benefits to heart health with moderate drinking, such as good cholesterol levels going up."
But "we know that even occasionally having higher amounts of alcohol can have detrimental effects," he says. "People who consume multiple servings of alcohol per day are at higher risk for cardiac problems in addition to some other ill health effects, including breast cancer risk in women and liver and throat disease."
Measuring Stroke Risk of Drinkers
In the Stroke Onset Study (SOS), researchers interviewed 390 people three days after they had an ischemic stroke. The most common type of stroke, ischemic strokes occur when blood flow to the brain is blocked by a blood clot. People whose ability to speak was impaired by their stroke were not included in the new study.
During the interviews, 14 people said they drank an alcoholic beverage within an hour of their stroke, 104 said they had a drink within the past 24 hours, and 248 said they had drunk alcohol in the past year, the researchers report.
Stroke risk was 2.3 times higher in that first hour after alcohol consumption, 60% higher in that second hour, and returned to normal risk thereafter, when compared with stroke risk in people who did not drink an alcoholic beverage during these time intervals. The findings held even after researchers took into account other factors known to affect stroke risk.
Now, Mittleman and colleagues plan look at how alcohol affects stroke risk over six months.
Calling the new study "intriguing," Irene Katzan, MD, director of the Primary Stroke Care Center at the Cleveland Clinic in Ohio, tells WebMD that the new research "seems to open the door for us to evaluate the phenomenon more closely."
The new study will not change how she talks to her patients about their drinking habits.
"The guidelines and general consensus state that one to two drinks a day is slightly beneficial at reducing risk of stroke and heart disease, and that heavy drinking is detrimental, and this study does not change that," she says.
However, "it's very interesting and should be further explored because if we better understand and characterize this phenomenon, it could potentially alter what we tell patients in the future."