Additive effects of depression and abdominal obesity on cognitive function in middle-aged and older population: evidence from multinational cohorts

This study aimed to investigate the joint trajectories of obesity/abdominal obesity and depression, and their association with cognitive function among four nationally representative cohorts. We used data from four nationally representative cohorts (China, UK, USA, and Mexico) in adults over the age of 45, which included a total of 114,633 participants. Kml3D clustering algorithm was conducted to identify the potential joint trajectories of obesity/abdominal obesity and depression of homogeneous groups. Generalized Estimating Equations (GEE) were performed to examine the joint trajectory of obesity/abdominal obesity and depression in relation to cognitive function. In all cohorts, the baseline "Comorbidity" (with both depression and obesity/abdominal obesity) exhibited significantly poorer performance on subsequent cognitive assessments compared to the "Neither condition" group (neither depression nor obesity). Cluster analysis and GEE revealed that when Body Mass Index (BMI) was used as an obesity indicator, individuals in the joint trajectory groups with depression trajectories (regardless of obesity trajectories) across four cohorts exhibited poorer cognitive performance compared to the Normal weight and No depressed group (CHARLS: β = − 0.35, 95% CI − 0.42 to − 0.28; ELSA: β = − 0.32, 95% CI − 0.44 to − 0.20; HRS: β = − 0.20, 95% CI − 0.27 to − 0.13, MHAS: β = − 0.15, 95% CI − 0.19 to − 0.10; all P < 0.001). Conversely, associations between the joint trajectory groups with obesity trajectories (regardless of depression trajectories) and cognitive function demonstrated significant heterogeneity across cohorts. Abdominal obesity measures indicated that the abdominal obesity or higher waist-to-height ratio (WHtR) and Depression group significantly contributed to cognitive decline compared to those in the No abdominal obesity and No depression group (CHARLS: β = − 0.31, 95% CI − 0.39 to − 0.23; ELSA: β = − 0.20, 95% CI 0.29 to − 0.12; HRS: β = − 0.20, 95% CI − 0.27 to − 0.14, all P < 0.001). Abdominal obesity and depression exert independent additive and fluctuating effects on measures of cognition in middle-aged and older persons. Strategies that broadly aim to decrease excess fat, notably abdominal obesity, represent near-term interventions that may beneficially influence aspects of cognition in depression.