Abstract
Studies show that light to moderate alcohol consumption is related to better health and higher cognitive performance. However, it has been suggested that this association is caused by a systematic bias in the control group as many people abstain from drinking or quit because of health issues. Therefore, the group of non-drinkers is biased towards poor health and may not be suitable as a control group. The present study examined the effect of alcohol on cognitive performance while addressing this bias by excluding the non-drinkers. Thus, instead of comparing different levels of alcohol consumption to a non-drinking control group, a dose-response association was calculated between all levels of alcohol intake and cognitive performance. The study used information from a sample of people in the Swedish Twin Registry, who in their midlife (1967) participated in a survey on alcohol intake and 25 years later participated in a longitudinal study on cognitive aging (N = 486). The cognitive aging study took place on five occasions, at 2-year intervals, and included the Mini Mental State Examination (MMSE), tests of episodic memory, semantic memory and spatial ability. The association between midlife alcohol consumption and later cognitive performance was analyzed using growth curve models, adjusting for background variables. The findings showed that there was a significant negative dose-response association between alcohol intake in midlife and the MMSE, and the tests of episodic memory, such that higher intake in midlife was related to lower performance in old age. The associations between alcohol and semantic memory, and spatial ability respectively, were not significant. In contrast to findings from other studies, which show that low to moderate alcohol intake promotes cognitive function, the current study showed that alcohol intake was related to lower cognitive performance in a dose-response manner, even at low levels. The results from this study indicate that the observed benefits of moderate alcohol intake for cognitive function reported by others might be solely due to comparisons to an inappropriate control group, a group that is biased towards poor health. Hence, it is concluded that light alcohol intake may not protect cognitive function.
Highlights
Many studies converge on the conclusion that long-term low to moderate alcohol intake protects against dementia and cognitive aging
The findings from Model 1, which controlled for demographic factors only, showed negative association between alcohol intake reported in midlife and cognitive function 25-years later, such that more drinking was significantly related to lower scores in the Mini Mental State Examination (MMSE), picture recognition, and prose recall
This indicates that there is a covariation between the effect of alcohol and the health-related factors, such that a part of the negative effect of alcohol on cognitive performance may have been caused by poor health
Summary
Many studies converge on the conclusion that long-term low to moderate alcohol intake protects against dementia and cognitive aging (for review, see Peters et al, 2008; Anstey et al, 2009). Other researchers point to methodological shortcomings of observational studies, one major critique being misclassification of abstainers It has been known for a long time that the group of alcohol abstainers is biased towards poor health (Shaper et al, 1988; Fillmore et al, 2006, 2007a,b, 2008). A recent systematic review and meta-analysis of studies investigating alcohol use and mortality risk showed that after adjustment for abstainer biases no significant reduction in mortality risk was observed for low-volume drinkers (Stockwell et al, 2016)
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