Preservation of cognitive function is one of the major concerns in contemporary ageing populations. Overweight and obesity, the prevalence of which have been increasing in many countries all over the world, have been identified as risk factors for poor health development: They appear to be related to several diseases including diabetes mellitus, hypertension, cardiovascular diseases, but also poor cognitive performance. At the same time, a phenomenon called “obesity paradox” or “jolly fat” is discussed in literature. It indicates a counterintuitive positive relation between (over-)weight and certain health outcomes, particularly for mental and cardiovascular diseases, but also for cognitive development.
This project examines the relationship between bodyweight change and the development of cognitive functioning in older age and challenges the notion of an obesity paradox in cognition. To this end, we use longitudinal data from the Survey of Health, Ageing and Retirement in Europe (SHARE) and employ asymmetric fixed effects regression, accounting for possible confounding variables such as age, grip strength, health conditions, and physical activity. Additionally, we investigate possible heterogeneity in the BMI-cognition relation.
We find a positive association between BMI change and change in cognitive performance, which is dominantly driven by BMI decrease. Weight loss is typically negatively related to cognitive decline, particularly at low levels of BMI and mainly due to health conditions affecting both bodyweight and cognitive performance. Weight gain is, on average, not significantly related to cognitive performance. However, respondents with preceding weight loss profit from small increases in BMI, while larger increases eventually become cognitively detrimental. Our findings provide no support for an obesity paradox in cognition. The association between weight change and cognitive performance in older age is based on weight changes being related to illness and recovery.
First results of this project have been published in the SHARE First Results “Health and Socio-economic Status over the Life Course”. A full paper based on extended and refined analyses has been published in PloS ONE.