The new study also showed that low to moderate alcohol intake did not lower their stroke risk, as some previous studies found.
While chronic alcohol abuse has been associated with brain volume loss, this study suggests that even moderate alcohol intake may promote brain atrophy, said Jingzhong Ding, Ph.D., lead author and a research associate at the Bloomberg School of Public Health at Johns Hopkins University in Baltimore. Brain atrophy may be associated with lower cognition and reduced extremity function.
Many studies have shown a strong correlation between heavy drinking and a higher risk of stroke and brain deterioration; however, evidence about the effects of low to moderate alcohol intake varies. Some studies have shown that alcohol intake is associated with reduced stroke risk in certain age groups, and others have found no correlation.
One study of people age 65 or older - the Cardiovascular Health Study - found that moderate alcohol intake was associated with fewer brain infarcts (dead tissue) and white matter lesions in the brain. However, moderate alcohol intake was also linked with brain atrophy (brain shrinkage).
Ding and colleagues from five other institutions assessed the relationship of alcohol intake with brain abnormalities in middle-aged adults. Cognitive decline is more common in older adults and alcohol consumption may change with aging. So, Ding felt that evaluating middle-aged adults could provide new evidence.
They used magnetic resonance imaging (MRI) to measure infarcts, changes in the inner matter of the brain known as white matter lesions, and brain atrophy. Infarcts and white matter lesions increase stroke risk.
The researchers randomly selected 2,821 participants, 55 years or older, from Forsyth County, N.C., and Jackson, Miss. who were participating in the Atherosclerosis Risk in Communities (ARIC) Study, a prospective, community-based investigation into the cause and natural development of atherosclerosis. Researchers used baseline information collected between 1987-89 and conducted follow-up examinations every three years until 1995. Participants were asked to have a brain MRI examination between 1993-95. After excluding those not eligible or those who declined to participate, 1,909 middle-aged adults (22 percent white men, 18 percent black men, 29 percent white women and 32 percent black women) underwent a brain MRI. Neuroradiologists then identified the presence of infarction, the extent of white matter lesions, and ventricular and sulcal size - void areas of the brain containing only cerebrospinal fluid.
Participants self-reported alcohol consumption, and were categorized into five groups: never drinkers, former drinkers, occasional drinkers (less than one drink per week), low drinkers (between one to six drinks per week), and moderate drinkers (seven to 14 drinks per week). Data on income, physical activity, cigarette smoking, cholesterol, hypertension, heart disease, diabetes, and stroke were also recorded.
In general, they found that as the level of alcohol intake increased, so did ventricular and sulcal size.
"There is no brain tissue in the ventricular and sulcal areas, as these areas are filled with cerebrospinal fluid," Ding said. "Therefore, an increase in ventricular and sulcal size indicates a reduction in the brain tissue, or brain atrophy, around the ventricular and sulcal areas."
Researchers observed no consistent association with infarction or white matter grade. Compared with never drinkers, former drinkers and moderate drinkers had higher odds of infarction without considering other factors. After adjusting for influencing factors, there was no protection from infarction associated with occasional or low drinking. There were also no consistent differences in white matter between current drinkers and never drinkers when looking at men and women and each racial group.
In general, both ventricular and sulcal size increased with higher alcohol intake among men, women, whites, and blacks, indicating a dose-response effect of alcohol consumption and brain atrophy. This finding suggests that the process might begin earlier in life than previously suggested.
However, the researchers note that the clinical significance of the small reduction of brain volume associated with moderate alcohol drinking is unknown.
"Because MRI measures in the brain were only conducted once during follow up, a causal relationship between alcohol intake and brain atrophy is difficult to establish," Ding said. Regardless of that limitation, he said, "the strength of the study lies in the large population-based sample and the consistency of the findings by gender and race."
"This study adds further to our knowledge concerning the effects of alcohol on the brain and provides new technology to investigate such issues," said Edgar J. Kenton, III, M.D., a spokesperson for the American Stroke Association.
Co-authors are Marsha L. Eigenbrodt, M.D.; Thomas H. Mosley, Jr., Ph.D.; Richard G. Hutchinson, M.D.; Aaron R. Folsom, M.D.; Tamara B. Harris, M.D.; and F. Javier Nieto, M.D., Ph.D. The study was partly funded by the National Heart, Lung, and Blood Institute.
Editor's note: For more information on stroke, visit the American Stroke Association Web site: strokeassociation.org.