Adults at least 65 years old, who consume between one and six alcoholic drinks each week, have a lower risk of dementia than those who do not drink, according to new findings published in the Journal of the American Medical Association (JAMA).However for heavier drinkers, the risk of the illness rises again.
"We found that abstainers had odds of dementia that were about twice as high as the odds of 'moderate drinkers'," explained the study's lead author Dr Kenneth Mukamal, from the Beth Israel Deaconess Medical Center (BIDMC)."Furthermore, those who drank 14 or more drinks per week also had a higher risk of dementia than the moderate drinkers."
The case control study compared the alcohol consumption patterns of 373 dementia patients with 373 control subjects who did not have dementia. The study subjects included both men and women who were screened from among 5,888 older adults participating in the Cardiovascular Health Study (CHS), a large cohort study sponsored by the US National Heart, Lung, Blood Institute.
The results showed a clear association between moderate alcohol consumption and reduced risk of dementia. Dementia was most commonly caused by either Alzheimer's disease or vascular dementia (as might develop following a series of strokes), according to Mukamal.
Dementia patients were identified through neurological and neuropsychiatric screening tests, including MRIs, between 1992 and 1999. Follow-up examinations were conducted each year. Alcohol consumption was determined during participants' yearly medical visits, at which time study subjects were asked to record the typical number of 12-ounce servings of beer, 6-ounce servings of wine, and shots of spirits they drank at a sitting, as well as the usual frequency with which they consumed these beverages.
The researchers adjusted for numerous factors - including age, sex, race, apoE4 status (a genetic risk factor for dementia), educational attainment, income, marital status, oestrogen replacement therapy, current and former cigarette smoking, diabetes, body mass index, physical activity, total cholesterol, atrial fibrillation, and history of congestive heart failure and stroke.
Mukamal and his team found abstainers had odds ratios of 1.00 for developing dementia, while those who consumed 14 or more drinks per week, had odds of 1.22. Moderate drinkers were the least likely to develop dementia, with odds of 0.46.
"Percentage-wise, this means that the moderate drinkers have a 54 per cent lower risk of dementia than the abstainers, while the heavier drinkers have a 22 per cent higher risk of dementia than the abstainers," added Mukamal. Heavier drinking was particularly linked to dementia among men - for whom the odds of dementia were doubled - and among participants who were positive for the apoE4 gene, for whom the risk of dementia was tripled.
Researchers believe that alcohol may protect against dementia by guarding against the development of cerebral arteriosclerosis or hardening of the arteries. Earlier work by Mukamal and colleagues found that light-to-moderate alcohol use was associated with a lower prevalence of white matter lesions in the brain and subclinical infarcts, neurological abnormalities which are believed to be related to blood-vessel functioning.
"There is a large body of literature concerning alcohol use and cognitive function, but to this point it hasn't been clear whether alcohol consumption is good, bad or neutral," said Mukamal. "This study for the first time looks at clinically diagnosed dementia in a large population of older adults who have more than one measurement of alcohol use."
However, he warned that they could not recommend that older adults begin drinking moderately "on the basis of these findings alone."