What does this study add? This meta-analysis critically looks at the dose-response relation between alcohol consumption and cognition. Major cognitive impairment, including dementia, is excluded. The study critically reviews the study designs to estimate the risk of bias.
The study includes 27 cohort studies, of which 18 studies examine the effect of different levels of alcohol consumption, and 10 provide data on a dose-response analysis.
Association per gender
Cognitive performance was slightly better for women drinking alcohol in moderation (less than 30 grams a day) compared to women that currently do not drink (see figure 1). The maximum cognitive performance is associated with about 1.5 drink a day (14.4 grams alcohol). However, the differences in cognition are small and the authors state that the evidence for a possible protective effect is of very low quality.
Figure 1: relation between alcohol consumption and cognition for women.
For men, the maximum cognitive performance related to alcohol consumption was even smaller and almost trivial. And again, the authors state that the evidence to support a possible protective effect of alcohol on cognition is of very low quality.
Figure 2: relation between alcohol consumption and cognition for men.
Excessive alcohol consumption
Excessive alcohol consumption (more than 55 grams of alcohol a day) may have detrimental effects on cognition, but the association was non-significant.
High risk of bias
For each study included in the meta-analysis, the authors checked for any potential bias. They conclude that there are serious concerns about the risk of bias due to the methods that the studies use. For example, all but three studies used a single assessment of alcohol consumption to estimate consumption, so most studies are unlikely to capture drinking patterns over time. And more importantly, almost all studies categorized alcohol intake based on current consumption, which means that former-drinkers are included in the group of non-drinkers. These former drinkers often have poorer self-reported health and higher levels of depression – both associated with cognition.
- Dose-response analysis
- Assessing risk of bias
Limitations
- Former drinkers could influence the relation
- Studies were heterogeneous
- Drinking pattern not included
- Observational research – causality cannot be proven
References
1. Brennan, S. E., McDonald, S., Page, M. J., Reid, J., Ward, S., Forbes, A. B., & McKenzie, J. E. (2020). Long-term effects of alcohol consumption on cognitive function: a systematic review and dose-response analysis of evidence published between 2007 and 2018. Systematic reviews, 9(1), 1-39.
2. Wiegmann, C., Mick, I., Brandl, E. J., Heinz, A., & Gutwinski, S. (2020). Alcohol and Dementia–What is the Link? A Systematic Review. Neuropsychiatric Disease and Treatment, 16, 87.
Photo credits: ‘Hersenen’ from Geralt.