Longitudinal muscle strength trajectories, incident depressive symptoms, and life satisfaction in Chinese middle-aged and older adults

BACKGROUND: Depression and life satisfaction are critical dimensions of mental health in aging populations. Although grip strength has an established association with depression, the role of its long-term trajectories on depression and their relationship with life satisfaction remain inadequately studied. METHODS: We utilized data from 3158 middle-aged and older adults in the China Health and Retirement Longitudinal Study. Group-based trajectory modeling was used to identify grip strength trajectories from 2011 to 2015. Secondary exposure was the magnitude of grip strength decline from 2011 to 2015. Multivariable-adjusted modified Poisson and logistic regression models were employed to assess associations between these trajectories and incident depressive symptoms or life satisfaction in 2018 and 2020. RESULTS: Three distinct declining grip strength trajectories were identified (high-baseline declining, medium-baseline declining, low-baseline declining). Among the participants, 859 (27.2%) developed depressive symptoms by 2018. Compared with the high-baseline declining group, the medium-baseline declining group had an approximately 26% (IRR 1.26, 95% CI 1.03-1.56) higher risk of depressive symptoms, and the low-baseline declining group had an approximately 70% (IRR 1.70, 95% CI 1.32-2.19) higher risk. Sex-specific dominant hand grip strength thresholds for risk stratification of depressive symptoms in middle-aged adults were identified (males, mild increase below 43.0 kg and significant increase below 33.0 kg; females, mild increase below 29.2 kg and significant increase below 21.9 kg). No such clear threshold was observed for older adults. After full adjustment for confounders, no independent association was observed between life satisfaction and any grip strength indicator, whether baseline level, trajectory, or rate of decline. CONCLUSIONS: Longitudinal grip strength trajectories significantly improve risk prediction of depressive symptoms compared with single-time-point measures and provide practical thresholds for risk stratification in middle-aged adults in clinical and community settings. Preserving muscle strength may represent a promising intervention strategy for depression prevention in middle-aged and older adults.