Longitudinal impact of metabolic syndrome and depressive symptoms on subsequent functional disability among middle-aged and older adults in China

Background: Few studies examining the impact of metabolic syndrome and depressive symptoms on subsequent functional disability are available. Objectives: To determine the impact of baseline metabolic syndrome and depressive symptoms on subsequent functional disability. Methods: This study used data from the 2011 baseline and 2013, 2015 and 2018 follow-up waves of the China Health and Retirement Longitudinal Study (CHARLS). Functional status was assessed by activities of daily living (ADLs) and instrumental ADLs (IADLs). Analyses were restricted to middle-aged and older adults (≥50 years) free of functional disability at baseline. Metabolic syndrome, depressive symptoms, and covariates were measured at baseline. New-onset ADL and IADL disability were obtained in follow-up measurements. Competitive risks based on survival analysis were conducted to examine the impact of baseline metabolic syndrome and depressive symptoms on subsequent functional disability after covariates were controlled. Results: Baseline depressive symptoms significantly predicted functional disability over a 7-year follow-up after adjusting for covariates (Hazard ratio [HR] = 1.54, 95% confidence intervals [CI] = 1.40–1.70 for ADL disability; HR=1.36, 95% CI=1.25–1.48 for IADL disability). Metabolic syndrome significantly predicted ADL disability (HR=1.25, 95% CI=1.14–1.38) but not IADL disability (HR=1.02, 95% CI=0.94–1.10). No significant additive interaction between metabolic syndrome and depressive symptoms on functional disability was found. Conclusion: The current study found that baseline depressive symptoms were significantly associated with both ADL and IADL disabilities, while metabolic syndrome significantly predicted ADL disability. In addition, some indications showed that the effect in those with both conditions was greater than the sum of the effects separately.