A number of prospective studies have shown that moderate drinkers are at lower risk of developing dementia or cognitive impairment than abstainers or heavy drinkers; possible mechanisms of a putative beneficial effect could relate to a reduction in the risk of cerebral atherosclerosis, a direct effect on cognition through the release of acetylcholine in the hippocampus, the antioxidant effects of alcohol and polyphenols, or from the down-regulation of inducible nitric synthase and up-regulation of endothelial nitric oxide synthase.
The present study is based on 1,309 women who were aged 65 years or greater at the beginning of a 20-year follow up, during which they had at least two assessments of cognitive function. At baseline, 42.1% of the women reported that they were “light” drinkers (>0 – < 3 drinks/week, 13.8% reported “moderate” consumption (3-7 drinks/week), and 3.6% reported “heavy” consumption (> 7 drinks/week). By the 20th year of follow up, 17.5% of the previously normal women had developed dementia (by several standard tests, a previous diagnosis of dementia, or nursing home residence), and 22.7% had developed mild cognitive impairment (MCI). Thus, a total of 40.2% of the women had developed some degree of cognitive impairment.
In this paper, there was no suggestion that the small percentage of women (5%) who increased their intake changed their risk of cognitive impairment (fully adjusted OR=1.04, 95% CI 0.56, 1.95), when compared with women who did not change their intake or decreased it only slightly. However, for women who decreased their intake by > 0.5 drinks/week, the authors suggest that there was an increase in risk of cognitive impairment, with unadjusted results showing an OR of 1.34, 95% CI: 1.05-1.70. However, with full adjustment for confounders, the effect was attenuated: OR = 1.26, 95% CI 0.98, 1.61; p = 0.07.
Forum members noted that the reasons that some women changed their drinking habits could not be ascertained (as is usually the case in observational studies). Alzheimer’s dementia has a long prodromal period and latent pathology could precede/contribute to a decrease in drinking. They were also concerned about the lack of cognitive characterization of the cohort at baseline. Thus, Forum members had some difficulty in knowing how to interpret the finding of a lack of association of baseline drinking with risk of cognitive impairment 20 years later given that we are not told whether the groups defined on baseline drinking differed from each other in age or other health risk factors. For those who changed their intake, decreasing drinking by > 0.5 glasses/week may be very different for someone drinking > 7 drinks/week than in someone drinking < 1 drink/week. It would have been better if the authors somehow took baseline drinking into account when assessing effects of change in drinking.
There was also the concern that any observational study that relates the effects of changes in alcohol intake on the risk of a disease without somehow taking earlier drinking into account may give paradoxical results. (An example is the relation of obesity to cardiovascular disease; overall, there is an increase in risk for obese individuals but when changes in intake among older people are evaluated, the result is often no effect or even a protective effect: the “obesity paradox.”) The same has been shown for the relation of usual alcohol intake and changes in intake to other diseases.
Thus, while the analyses were done appropriately, Forum members had concerns about whether the findings presented in this paper justify the wisdom of the authors in stating in their conclusion that “Women in their ninth and tenth decade of life who decrease alcohol use may be at risk of cognitive impairment.” As one reviewer stated: “Knowing from other studies that light to moderate alcohol consumption is good for the heart and the head, I would not advise elderly people to stop drinking. However, the conclusions of the authors that this paper shows that decreasing alcohol consumption increases the risk of cognitive impairment in elderly women may be true, but are not justified because the design, analysis, and results of the study do not permit such a statement.”
Reference: Hoang TD, Byers AL, Barnes DE, Yaffe K. Alcohol Consumption Patterns and Cognitive Impairment in Older Women. Am J Geriatr Psychiatry 2014; 22:1663-1667.