Interaction effects of handgrip strength and depressive symptoms on the risk of functional disability among middle-aged and older adults

Evidence regarding the combined effects of handgrip strength (HGS) and depressive symptoms on functional disability remains scarce. This study aimed to examine the additive interaction between HGS and depressive symptoms on functional disability among Chinese middle-aged and older adults. Data were extracted from 8,594 participants in the 2015–2020 waves of the China Health and Retirement Longitudinal Study (CHARLS). Abnormal HGS was defined using the cut-off points recommended by the Asian Working Group for Sarcopenia (AWGS). Depressive symptoms and functional disability were measured using the Center for Epidemiologic Studies Depression Scale and an 11-item ADLs scale, respectively. Logistic regression models were employed to evaluate the additive interaction between abnormal HGS and depressive symptoms on functional disability. Over a 5-year follow-up, 2,658 (30.9%) participants developed functional disability. Compared with those with normal HGS and without depressive symptoms, participants with abnormal HGS and depressive symptoms showed significantly increased risks of functional disability (ADL: adjusted OR = 4.87, 95% CI: 3.58–6.65; BADL: OR = 3.74, 95% CI: 2.82–4.97; IADL: OR = 4.23, 95% CI: 3.18–5.62). Moreover, the synergistic interaction effect between abnormal HGS and depressive symptoms on functional disability was observed by attributable proportion due to interaction (AP = 0.35, 95% CI: 0.13–0.56), particularly among males (AP = 0.36, 95% CI: 0.07–0.66) and middle-aged adults (AP = 0.44, 95% CI: 0.14–0.74). Abnormal HGS and depressive symptoms synergistically increased the risk of functional disability, highlighting the need for integrated interventions that simultaneously preserve muscle strength and promote psychological well-being to prevent or delay functional decline in middle-aged and older adults.