Longitudinal association between muscle strength and depression in middle-aged and older adults: A 7-year prospective cohort study in China

Background: Evidence regarding the associations between muscle strength in different parts of the body and depression is lacking. This study examined whether poor muscle strength is associated with a higher incidence of depression in a large cohort of middle-aged and older adults. Methods: In total, 5,228 middle-aged and older adults from the China Health and Retirement Longitudinal Study without depression at baseline were followed for 7 years. Their demographic characteristics, chronic diseases and lifestyle behaviors were assessed. After adjusting for relevant variables, a Cox regression was used to determine the relationship between muscle strength and incident depression. Results: Over 32,544 person-years of follow-up, 1,490 participants developed depression. Low muscle strength at baseline was associated with a higher 7-year incident of depression, even after excluding those who developed depression within 2 years. After adjusting for confounding factors, it was found that a higher baseline relative handgrip strength was a protective factor against depression (HR [95% CI]=0.575 [0.430-0.768] for the lowest quartile vs. the highest quartile; p<0.001). Longer times on the 5TSTS test were a risk factor for depression (HR [95% CI]=1.321 [1.077-1.621] for the lowest quartile vs. the highest quartile; p = 0.007). When the strengths of the upper and lower limbs were considered together, the hazard ratio for depression in people with relatively greater muscle strength was 0.463 (95% CI=0.307-0.699; p<0.001). Conclusions: Muscle strength could be predictive of depression, and the combined measurement of upper and lower limb muscle strength can improve the predictive ability.