The association of grip strength with depressive symptoms and cortisol in hair: a cross-sectional study of older adults

Background: Low handgrip strength has been shown to be associated with higher levels of depressive symptoms. One area of mental health that is understudied in relation to grip strength is chronic stress, which can exist independently to depression, or as a comorbidity or precursor to this condition. The present study examined cross-sectional associations between grip strength, an established marker of physical function, and (i) depressive symptoms and (ii) chronic stress utilising hair cortisol concentrations, while accounting for multiple pertinent confounding variables. Method: Data were used from wave 6 (2012/13) of the English Longitudinal Study of Ageing, a panel study of older (≥50y) community-dwelling men and women. Grip strength was measured in kg using a handheld dynamometer. Depressive symptoms were assessed using the 8-item Center for Epidemiologic Studies Depression scale. Hair cortisol concentrations (pg/mg) were determined from samples of scalp hair and log-transformed for analysis to correct skewness. Associations of grip strength with depressive symptoms and hair cortisol concentration were tested using linear regression models adjusted for age, sex, ethnicity, wealth, smoking status, physical activity, body mass index, limiting long-standing illness, arthritis, diabetes, and hair treatment. Results: The sample comprised 3,741 participants (mean age 68.4 years, 66.4% female). After adjustment for age and sex, grip strength was significantly and negatively associated with both depressive symptoms (B=-0.038, SE=0.004, p<0.001) and hair cortisol (B=-0.003, SE=0.001, p=0.029). However, in the fully-adjusted models, both associations were attenuated and only the association with depressive symptoms remained statistically significant (B=-0.015, SE=0.004, p<0.001; hair cortisol B=-0.002, SE=0.001, p=0.088). Conclusion: In a large sample of older adults in England, grip strength was negatively associated with depressive symptoms. Results were inconclusive regarding the association between grip strength and chronic stress. Further research examining the longitudinal relationships between muscular strength and specific aspects of mental health, while also exploring the neurobiological mechanisms underlying these associations, is warranted before recommendations for policy and practice can be made.