That's the surprising conclusion of new research in the March 19 issue of the Journal of the American Medical Association.
While there have been several studies on alcohol and cognitive functioning, the results have been mixed, says the new study's author, Dr. Kenneth J. Mukamal, an internist at Beth Israel Deaconess Medical Center in Boston.
In the last three to four years, however, larger studies have been suggesting that moderate drinkers do seem to have a lower risk of dementia, he adds.
The current study appears to be the largest to look at this in detail, Mukamal says, and also includes repeated assessments of how much people were drinking before joining up with the study.
Mukamal and his colleagues looked at 373 people with a recent onset of dementia and 373 controls who were among the 5,888 participants in the Cardiovascular Health Study. All of the participants were 65 or older.
Those who consumed one to six drinks a week had the lowest odds of developing dementia -- a 54 percent lower risk than those who abstained. Those who had between zero and one drink a week had a 35 percent lower risk; those who consumed seven to 13 drinks a week a 31 percent lower risk; and those who consumed 14 to 21 drinks a week a 22 percent greater risk.
The association between moderate drinking and dementia was similar for men and women, but the risks of heavier drinking seemed to be more apparent among the men, Mukamal says.
"Maybe men who drink heavily tend to drink more heavily than women who drink heavily," he speculates. "There may also be some issue of context. Men who drink heavily may be doing so alone. Women who drink that amount may be doing so on a more social basis and there's some thinking that social contacts can ward off dementia."
The exact biological mechanisms are still unclear, although there is speculation. Previous work has shown that light and moderate drinkers had fewer white matter lesions, which scientists think might be linked to blood vessel blockages. Such blockages are implicated in heart attacks and in dementia.
"Much like alcohol consumption is supposed to prevent heart attacks by preventing blockages in blood vessels, the same thing might be happening in dementia," Mukamal says. "By preserving blood flow to the brain, we could hold off dementia."
The results are still not convincing to all experts.
"It's very difficult to conclude whether alcohol has any impact on your risk for dementia," says Dr. Antonio Convit, an associate professor of psychiatry and medical director of the Center for Brain Health at New York University School of Medicine in New York City. "The more you know, the more you realize that these studies are not all pointing in the same direction."
In particular, Convit points to the famed Rotterdam Study, which found that one to two drinks per day was the most beneficial amount but only for men. The new study found those levels actually increased the risk of dementia.
Part of the discrepancy may be explained by the fact that the Rotterdam population was younger (participants were 55 and older), Mukamal says.
Still, Convit is not planning to revise what he tells his patients anytime soon.
"Because of the known cardiovascular benefits, I would tell them moderate amounts of alcohol -- one drink a day -- certainly doesn't seem like it's going to harm you," he says. "But [concerning] dementia, there's zero benefit that I can see from these studies."
Mukamal agrees with that recommendation.
"For people in this age group, alcohol interacts with a lot of medications," he says. "It's not a simple thing to make any sort of recommendation, but for people who are drinking more than one to six drinks a week, this might be a reason to cut back. The current guidelines say no more than one a day for older adults, and this fits nicely with that."
Alzheimer's disease, which is just one form of dementia, currently affects 4 million people in the United States, with 360,000 new cases diagnosed each year. The total number of people with dementia is much larger.
For more on Alzheimer's disease, visit the Alzheimer's Association.
The American Psychological Association has information on age-related cognitive changes.