New research suggests that older adults who have no history of dementia reduce their chances of developing dementia by regular moderate drinking.

However in people 75 and older who have been diagnosed with mild cognitive impairment or memory loss alcohol, irrespective of the amount alcohol accelerates the rate of memory decline.

The study authors define “moderate” as one or two drinks a day and was associated with a nearly 40% drop in dementia risk compared to non-drinkers. 

Study author Dr. Kaycee M. Sink, an assistant professor of medicine with the department of internal medicine in the Gerontology and Geriatric Medicine section at Wake Forest University School of Medicine in Winston-Salem, N.C. said, "We found that for cognitively normal older adults, the lowest risk of dementia was for those who drank an average of one to two alcoholic drinks per day. However, for older adults who started the study with mild cognitive impairment, alcohol use was not protective."

The researchers followed 3069 people 75 and older, of whom 482 had been diagnosed with mild cognitive impairment at the start of the study, for six years.

The participants reported their drinking habits and based on alcohol consumption were divided into 4 groups: abstinent, light (one to seven drinks a week), moderate (eight to 14 drinks a week), and heavy (more than 14 drinks a week).

The researchers found apart from the 482 participants with mild cognitive impairment seen initially, 523 new cases of dementia were diagnosed. They noted that people who drank one to two drinks a day were 37% less likely to develop dementia than teetotalers and it didn't matter whether they drank wine, beer, or hard liquor. The risk reduction was similar to exercising three times a week or more, said Sink.

In the case of the people who had mild cognitive impairment at the start of the study those who drank more than two drinks a day were nearly twice as likely to develop dementia, compared with nondrinkers. Smoking, education, depression, and other factors that can affect the risk of dementia were taken into account.

"Based on this study, we cannot recommend that older adults who don't drink start drinking alcohol," Sink said. "But it is reasonable to say that if you are already a light to moderate drinker, you may be at a lower risk of developing Alzheimer's disease or other dementias. However, if you already have memory or thinking problems, drinking alcohol may accelerate memory decline."

Sink added that the protective effect could be due to alcohol itself or some other lifestyle factor shared by moderate drinkers.  The findings were presented at the Alzheimer's Association 2009 International Conference on Alzheimer's Disease.

Sink said in the case of people with mild cognitive impairment no benefit was seen as any benefits from alcohol may not have been strong enough to slow the degenerative disease process that's already kicked in.

Greg M. Cole, associate director of the Alzheimer's Disease Research Center at the UCLA David Geffen School of Medicine in Los Angeles said, "Alzheimer's has a strong overlap with cardiovascular disease. And you have had a number of studies that have associated reduced cardiovascular disease risk with a rise in HDL levels -- so-called 'good' cholesterol' -- that can come with consuming small amounts of alcohol. And it has been thought that this could potentially impact in a positive way on the risk for vascular dementia and Alzheimer's. So there is a solid rationale for this finding."