Metabolic syndrome in the association of BMI and trajectory of depressive symptoms in middle-aged and elderly population: a cohort study from China.

Abstract

This study aimed to investigate the cross-sectional and longitudinal relationship between BMI and depressive symptoms among adults aged over 45 and further explore the mediating role of metabolic syndrome. Our data were drawn from the China Health and Retirement Longitudinal Study. BMI was categorized into: underweight (≤18.5 kg/m²), healthy weight (18.5-23.0 kg/m²), overweight (23.0-27.5 kg/m²), and obesity (≥27.5 kg/m²). The Group-based trajectory modeling was used to identify trajectories of depressive symptoms. The logistic regression models were performed to estimate the odds ratio (OR) and 95% confidence intervals (95% CI) between BMI and depressive symptoms. A total of 13,422 participants were enrolled in the cross-sectional analysis and 10,136 individuals were included in the longitudinal study. Two trajectories of depressive symptoms were identified: low-stable trajectory and high-ascending trajectory. Individuals with underweight exhibited higher risks of depressive symptoms (OR = 1.20, 95% CI: 1.01-1.43) and were more likely to follow the high-ascending trajectory (OR = 1.29, 95% CI: 1.04-1.61) compared with those with healthy weight. Conversely, participants with overweight and obesity had reduced risks of depressive symptoms (overweight: OR = 0.87, 95% CI: 0.80-0.95; obesity: OR = 0.83, 95% CI: 0.74-0.94) and were less likely to follow the high-ascending trajectory (overweight: OR = 0.85, 95% CI: 0.76-0.95; obesity: OR = 0.85, 95% CI: 0.72-0.99). Furthermore, metabolic syndrome accounted for 31.87% of the association between BMI and depressive symptoms and 50.60% of the association between BMI and depressive symptom trajectory. Underweight was a risk factor for depressive symptoms and high-ascending trajectory of depressive symptoms. Medical professionals should pay attention to the mental status of middle-aged and older adults with underweight and interventions of improving metabolic syndrome could protect mental health.