ANAHEIM, Calif., Feb. 7 -- A bit of alcohol can protect against stroke, but even a little cigarette smoke carries a hidden stroke risk, researchers reported here today at the American Heart Association's 22nd International Joint Conference on Stroke and Cerebral Circulation.
Light or occasional alcohol consumption lowered stroke risk by up to 62 percent compared to non-drinkers in a New York City study. But people who had at least five drinks daily tripled their stroke risk.
Researchers in Winston-Salem, N.C., found that current and former smokers had a significantly increased risk of so-called silent stroke compared to people who never smoked. But the study also showed about a 20 percent increase in the prevalence of silent stroke in non-smokers exposed to environmental tobacco smoke.
Silent stroke refers to reduced blood flow in brain arteries without the accompanying symptoms of stroke.
Alcohol and stroke have shared a controversial relationship, said Ralph L. Sacco, M.D., a stroke specialist at Columbia-Presbyterian Medical Center in New York City. Some studies have suggested that excessive drinking increases stroke risk. Other studies have hinted at a protective effect from modest consumption.
"The protective effect hasn't been seen in all populations, particularly African Americans," said Sacco, director of the ongoing Northern Manhattan Stroke Study. "Studies also have been unclear about the amount of alcohol that is protective."
He and his colleagues examined alcohol consumption during the 12 month period that preceded a stroke in 423 patients and compared those findings with year-long alcohol consumption in 793 people with no history of stroke. The two groups were matched for age, sex and race. Hispanics accounted more than half the populations of both groups. African Americans comprised about 30 percent of each group.
After adjusting for such stroke risk factors as high blood pressure, diabetes, coronary artery disease and smoking, the scientists correlated alcohol intake with stroke risk. They defined a drink as a standard shot of liquor (1.5 ounces), one beer (12 ounces) or four ounces of wine.
Occasional drinkers -- who consumed less than one drink per month -- had a 62 percent lower risk of stroke than people who never drank. For people who consumed up to two alcoholic drinks per day, stroke risk was 45 percent lower compared to non-drinkers. Both differences were statistically significant.
When alcohol consumption ranged between 2 and 4 drinks daily, the association with stroke risk become less clear. Although 27 percent lower than the risk for nondrinkers, the association was no longer statistically significant.
But consumption of more than five drinks daily more than tripled the risk of stroke.
The protective effect of occasional and light drinking held up for men and women, for different age groups and for all racial and ethnic subgroups. The study also produced some evidence that formerly heavy drinkers who had cut back to light or occasional consumption enjoy similar protective benefits.
"Drinking heavily in the past doesn't seem to have the same effect as current heavy drinking," Sacco said. "That implies that reforming your habits can have an impact on reducing your stroke risk."
This study was supported by two grants from the National Institute of Neurological Disorders and Stroke.
George Howard, Dr.P.H., and his colleagues at Bowman Gray School of Medicine evaluated the prevalence of stroke-like brain lesions in people who had no reported history of stroke or transient ischemic attack (TIA). These "little strokes" occur when a blood clot temporarily interrupts blood flow to the brain. About 36 percent of people who experience a TIA will later have a stroke.
The 1,805 people whose brains were studied were characterized as current smokers (330), past smokers (666), people who have never smoked but were regularly exposed to environmental smoke (669) and people who have never smoked and have not been exposed to environmental smoke (140).
Overall, 282 individuals had stroke-like brain lesions. Cigarette smoking proved to be a strong predictor of silent stroke, doubling the risk compared to people who have never smoked. Former smokers had a 50 percent higher prevalence of silent stroke, compared to non-smokers.
Non-smokers exposed to environmental smoke had a bout a 20 percent increased prevalence of the stroke-like lesions, a finding that was provocative but not statistically significant, said Howard.
"From a strictly scientific perspective, I cannot say that passive smoking is associated with these silent lesions," he explained. "But I do believe there is an association. You clearly see a dose-response relationship that increases fairly nicely across the spectrum of exposure to tobacco smoke, beginning with passive smoking."
The findings are consistent with previous Bowman Gray studies showing an association between exposure to environmental smoke and increased thickening of the carotid arteries, which supply the brain with blood. Thickened carotid arteries also increase the risk of stroke.