A new study led by researchers at Beth Israel Deaconess Medical Center (BIDMC) and the Harvard School of Public Health (HSPH) has found that heavy drinkers -- men who consume an average of three or more alcoholic beverages per day -- are nearly 45 percent more likely to suffer an ischemic stroke compared with nondrinkers.
The study also found that while light and moderate drinkers appear to be at neither greater risk nor greater advantage than abstainers when it comes to ischemic stroke, the frequency with which they consume alcohol may modestly influence their risk.
The findings, reported in the January 4, 2005 issue of the Annals of Internal Medicine, help shed light on a subject that has been the source of some confusion, and reinforce the importance of what the authors call "drinking patterns," the number of days per week that alcohol is consumed and the amount consumed on drinking days.
"In this study, the participants who were at lowest risk for stroke were the men who consumed one or two drinks on three to four days of the week," says lead author Kenneth Mukamal, MD, MPH, a general internist at BIDMC and Assistant Professor of Medicine at Harvard Medical School. "The importance of drinking pattern for stroke risk parallels our previous findings among this same group of men regarding alcohol consumption and the risk of developing diabetes and coronary heart disease. Among all three types of disease, the lowest risk seems to occur when consumption is limited to one or, at most, two drinks, approximately every other day, with little benefit shown above three to four drinking days per week."
Nearly 700,000 individuals in the U.S. suffer an ischemic stroke each year. Sometimes referred to as a "brain attack," the condition develops when an artery in the brain becomes blocked by a blood clot. There are two types of ischemic stroke: thrombotic, which results from the development of a blood clot within the brain itself, and embolic, which is the result of a clot traveling through the bloodstream from another part of the body and becoming lodged in the brain. In both instances, the ensuing deprivation of oxygen and nutrients to the brain can result in neurological damage or death.
During the course of the 14-year study the authors followed 38,156 participants who are part of the HSPH-based Health Professionals Follow-up Study. Beginning in 1986 and continuing every four years thereafter until 2000, the male participants, who ranged in age from 40 to 75, responded to a detailed questionnaire regarding diet and medical history, including alcohol consumption.
The researchers examined the following factors to gauge the influence of alcohol consumption on the risk for ischemic stroke: average amount of alcohol consumed; drinking patterns (number of days per week alcohol was consumed); and type of beverage consumed (beer, red wine, white wine, or spirits). They also looked at the incidence of both subtypes of ischemic stroke – thrombotic and embolic. During the course of the study, they confirmed 412 cases of ischemic stroke among the study participants.
Their findings showed that men whose average alcohol intake was three or more drinks per day had a 42 percent higher risk of ischemic stroke (particularly embolic stroke) than did abstainers. This finding, says Mukamal, may be attributable to alcohol's association with both high blood pressure and atrial fibrillation.
Although the findings also found that average intake of lower amounts of alcohol was associated with neither a significantly higher nor lower risk of stroke, when drinking frequency was taken into account, the light and moderate drinkers who consumed alcohol three to four days per week had a modest 32 percent lower stroke risk than did nondrinkers.
"I think there has been a subtle assumption that moderate drinking is associated with a lower risk of ischemic stroke, similar to the way that it is associated with a lower risk of heart attack," says Mukamal. "But our study did not demonstrate a statistically significant role for alcohol in guarding against stroke. While there does appear to be a small window for which light drinking is associated with lower risk, it's important to note that this window is smaller than it is for heart disease and therefore you cannot simply extrapolate between the two."
Mukamal notes that red wine appeared to offer slightly more protection than other types of alcohol, with red-wine drinkers shown to be at 23 percent lower risk of ischemic stroke. (Intake of one or more glasses per day was linked to a 46 percent lower risk, but few men in this study drank red wine on a daily basis, he adds.)
"Compared with other types of alcohol, red wine was associated with a step-wise lower risk of ischemic stroke," according to Mukamal. "This is curious, because among this population of men, red wine is not linked to a lower risk of heart disease any more than any other type of alcohol, so it's unclear why this would be the case with stroke." He adds that further research will be needed to help clarify this finding.
For now, the standard recommendation that men drink no more than two drinks per drinking day still appears to be a good one, say the authors.
"Our findings directly support current public health recommendations stating that men should consume less than two drinks per day," the authors write. "At the same time, our findings support the safety of continued light alcohol consumption among adults who have been able to appropriately regulate the quality and timing of their alcohol use."
Study coauthors include senior author Eric Rimm, ScD, Walter Willett, MD, DrPH, Alberto Ascherio, MD, DrPH, Ichiro Kawachi, MD, PhD, and Meir Stampfer, MD, DrPH, of the Harvard School of Public Health; Murray Mittleman, MD, DrPH, of Beth Israel Deaconess Medical Center; Katherine Conigrave, MD, of Royal Prince Albert Hospital, Camperdown, Australia; and Carlos Camargo Jr., MD, DrPH, of Massachusetts General Hospital.