A limited number of studies have found a J- or U-shaped relationship between the volume of alcohol consumed and long-term cognitive decline, suggesting light to moderate alcohol consumption is a positive predictor of health status in older adults, protects cognition and may reduce the risk of dementia in later life. Recent reviews and meta-analyses indicate, however, that there is little consensus on the level of alcohol consumption at which the harmful effects of alcohol on cognition emerge.
A study examined the shape of the association between alcohol consumption and change in cognitive performance. Data from 13,342 men and women, aged between 40 and 73 years were used in regression analysis that tested the functional relationship and the impact of alcohol on cognitive performance. Performance was measured using mean reaction time (RT) and intra-individual variation (IIV) in RT, collected in response to a perceptual matching task. Covariates included body mass index, physical activity, tobacco use, socioeconomic status, education and baseline cognitive function. A restricted cubic spline regression with three knots showed how the linear and non-linear effects of alcohol use on mean RT and IIV in RT were significant, adjusting for covariates.
In the 13,342 weekly drinkers, 5-year change in mean RT and IIV in RT were found to have curvilinear associations with alcohol consumption. Cognitive performance improved as alcohol consumption increased up to 10 g/day and then deteriorated as alcohol consumption increased beyond 10 g/day. The results indicate that as individuals age, this deleterious effect of alcohol on cognitive performance became more pronounced. The authors point out that the restricted cubic spline method enables the inflexion point in the curve to be identified but assumes linearity before and after the inflexion. They state “This assumption is unlikely to make much impact below the inflexion point due to the limited scale range (the proximity of zero), but it is a strong assumption above the inflexion point. They state that the wide confidence intervals on the curve above the inflexion (Fig. 1) indicate that further work is required to reduce uncertainty in the functional relationship between cognitive performance and alcohol consumption above 10 g/day.” They conclude, however, that the “Current advice from the UK Department of Health is for men and women to not consume more than 16g of pure alcohol per day (two units) on average. Findings reported here suggest that daily alcohol consumption above one unit may have an adverse cognitive impact. Recommendations should be sensitive to this, especially among middle-aged and older members of the population”.
David Spiegelhalter, Statistician and Chair of The Winton Centre for Risk and Evidence Communication, Cambridge has questioned the authors’ conclusions. In his blog, he stated “The response times improve rather dramatically with increasing alcohol consumption, down to a minimum when daily alcohol consumption is around 16g, which is exactly the two units a day under current guidelines. Then there is a (rather gentle) slowing in reaction times for increasing consumption up to very heavy drinking. The confidence intervals are very wide, but the estimated response time at two units a day is clearly estimated to be lower than at one unit a day, so if anything the study supports the current guidelines”.
Source: The relationship between alcohol use and long-term cognitive decline in middle and late life: a longitudinal analysis using UK Biobank. G Piumatti SC Moore, DM Berridge, C Sarkar, J Gallacher. Journal of Public Health. doi.org/10.1093/pubmed/fdx186