Older women who enjoy having a glass of wine with dinner or an occasional nightcap may be helping to prevent the onset of dementia, a new study suggests.

As part of the ongoing Nurses' Health Study, researchers in the U.S. looked at almost 12,500 women between the ages of 70 and 81 for up to 15 years.

The team tracked the women's alcohol consumption, and tested their memory and concentration. The study appears in Thursday's issue of The New England Journal of Medicine.

Low-to-moderate consumption of alcohol shows health benefits.

Researchers found women who drank an average of one drink per day had a 20 per cent lower risk of cognitive impairment, compared to nondrinkers.

Drinking less than 15 grams of alcohol per day in wine, beer and spirits all showed benefits.

Doctors who study Alzheimer's and other forms of dementia say it makes sense that alcohol protects the brain since it's been shown to protect the heart.

Francine Grodstein

One theory suggests alcohol improves blood flow to both organs.

"There's a lot of evidence now that the same kind of things that are good for your overall cardiovascular system are good for your brain as well," said the study author and epidemiologist Francine Grodstein of Brigham and Women's Hospital in Boston.

But it's impossible to say for sure that it's the alcohol alone that helps cognitive abilities based on an observational study like this one.

The study's authors aren't sure that having more than one drink a day is beneficial since there weren't enough women in the study drinking that much to draw conclusions.

The findings probably apply to men as well as women, although other studies with more measurements over time are needed.

The take-home message is, "If you would like to enjoy a glass of red wine with your dinner go ahead and enjoy it," said Carol Greenwood, a nutritional scientist at Toronto's Baycrest Centre.

In an editorial accompanying the study, Dr. Denis Evans and Julia Bienias said those seeking to "maximize cognition in old age" should keep in mind the harmful effects of alcohol abuse.

For those who can't drink alcohol or prefer not to, experts say diet and exercise can be just as beneficial for the heart and, by extension, the brain.