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An extensive review of the effects of alcohol consumption on the risk of cognitive impairment and dementia

Neafsey EJ, Collins MA.  Moderate alcohol consumption and cognitive risk.  Neuropsychiatric Disease and Treatment 2011:7:465–484.
Authors’ Abstract
We reviewed 143 papers that described the relationship between moderate drinking of alcohol and some aspect of cognition.  Two types of papers were found: (1) those that provided ratios of risk between drinkers and nondrinkers (74 papers in total) and (2) those that, although they did not provide such ratios, allowed cognition in drinkers to be rated as “better,” “no different,” or “worse” than cognition in nondrinkers (69 papers in total).
The history of research on moderate drinking and cognition can be divided into two eras: 1977–1997 and 1998–present.  Phase I (1977–1997) was the era of neuropsychological evaluation involving mostly young to middle-aged (18–50 years old) subjects.  Although initial studies indicated moderate drinking impaired cognition, many later studies failed to confirm this, instead finding no difference in cognition between drinkers and nondrinkers.
Phase II (1998–present) was and is the era of mental status exam evaluation involving mostly older (≥55 years old) subjects.  These studies overwhelmingly found that moderate drinking either reduced or had no effect on the risk of dementia or cognitive impairment.  When all the ratios of risk from all the studies in phase II providing such ratios are entered into a comprehensive meta-analysis, the average ratio of risk for cognitive risk (dementia or cognitive impairment/decline) associated with moderate “social” (not alcoholic) drinking of alcohol is 0.77, with nondrinkers as the reference group.  The benefit of moderate drinking applied to all forms of dementia (dementia unspecified, Alzheimer’s disease, and vascular dementia) and to cognitive impairment (low test scores), but no significant benefit against cognitive decline (rate of decline in test scores) was found.  Both light and moderate drinking provided a similar benefit, but heavy drinking was associated with nonsignificantly higher cognitive risk for dementia and cognitive impairment.
Although the meta-analysis also indicated that wine was better than beer or spirits, this was based on a relatively small number of studies because most studies did not distinguish among these different types of alcohol.  Furthermore, a number of the studies that did make the distinction reported no difference among the effects of these different types of alcohol.  Therefore, at present this question remains unanswered.  Analysis also showed that the presence of the apolipoprotein E epsilon 4 allele eliminated the benefit of moderate drinking.  However, this was based on a relatively small number of studies and several other studies have found a beneficial effect of the epsilon e4 allele.  Further studies are necessary to settle this question.  The benefit of moderate alcohol for cognition was seen in both men and women, although the amount and pattern of drinking is very different between the two sexes.  Lastly, the finding of unaffected or significantly reduced cognitive risk in light to moderate drinkers was seen in 14/19 countries for which country-specific ratio data were available, with three of the five remaining countries showing nonsignificant reductions as well.
ISFAR Forum summary
 The authors of this paper have carried out an excellent review of the relation of alcohol consumption to the risk of cognitive impairment and dementia.  They reviewed a total of 143 previous publications on the topic. There were 74 studies, based on a total of more than 250,000 subjects, that provided risk estimates for varying levels of alcohol consumption which allowed the investigators to include them in a comprehensive meta-analysis.  These papers were published mainly after 1998, were predominantly among older subjects (92% were ≥ 55 years of age and 70% ≥ 65 years of age), and almost all employed mental status examinations to define cognitive impairment/dementia.
As stated by the authors, “These studies overwhelmingly found that moderate drinking either reduced or had no effect on the risk of dementia or cognitive impairment.”  Overall, in the new meta-analysis based on these studies, the average ratio of risk for cognitive risk associated with moderate drinking of alcohol was 0.77, with nondrinkers as the reference group.  This estimate is close to the estimates of reduction in the risk of cognitive dysfunction (RR of 0.73 and 0.74) seen in other recent selective meta-analyses.  The present study found that both light and moderate drinking provided a similar benefit, but heavy drinking was associated with non-significantly higher cognitive risk for dementia and cognitive impairment.
Forum reviewers of this paper were particularly pleased that the authors attempted to answer a number of specific questions on this topic that have been raised from previous research.  Their results included finding no appreciable differences whether or not “sick quitters” were included in the reference group, little effect from adjustments for other lifestyle factors, and no significant differences between alcohol’s effects on dementia, Alzheimer’s dementia, or vascular dementia (but, based on a small number of studies, no significant reduction in risk of cognitive decline over time).  The investigators concluded that there were no differences between results in men and women.  Their analyses also led to the conclusion that wine is associated with more beneficial effects on cognition than beer or spirits, but the authors caution that these results are based on a limited number of reports, and that many studies show no significant differences according to type of beverage.
Forum reviewers agreed with the conclusions of the authors that “Overall, light to moderate drinking does not appear to impair cognition in younger subjects and actually seems to reduce the risk of dementia and cognitive decline in older subjects.”
For the full critique of this paper by members of the International Scientific Forum on Alcohol Research, visit www.bu.edu/alcohol-forum/critique-053-an-extensive-review-of-the-effects-of-alcohol-consumption-on-the-risk-of-cognitive-impairment-and-dementia-25-august-2011

 

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