The risk of dementia is also higher with heavier drinking, but only among those carrying a particular gene (apolipoprotein e4 allele) a known genetic risk factor for dementia.
The study involved 1,018 men and women aged 65-79 years whose physical and mental health was monitored for an average of 23 years. Alcohol consumption was recorded and blood samples were taken to determine apolipoprotein E genotypes.
Participants who drank no alcohol and those who drank alcohol frequently (several times a month) were both twice as likely to have mild cognitive impairment in old age than those who drank infrequently (less than once a month).
Only carriers of the apolipoprotein e4 allele had an increased risk of dementia with increasing alcohol consumption, suggesting that this particular gene may modify the effect of alcohol on the brain. These data indicate that frequent alcohol drinking has harmful effects on the brain, and this may be more pronounced if there is genetic susceptibility, say the authors.
Although these results agree with previous claims that light to moderate drinking might have a protective effect on the brain compared to total abstention and heavy drinking, the authors stress that an explanation for this remains to be clarified.
"We therefore do not want to encourage people to drink more alcohol in the belief that they are protecting themselves against dementia," they conclude.