Association between frailty and cognitive function in older Chinese people: A moderated mediation of social relationships and depressive symptoms

Background: To date, few studies have focused on examining either the direct or indirect effect of physical frailty on cognitive impairment. This study aimed to investigate the moderating effects of social relationships, including their individual components in the role of depressive symptoms as a mediator between frailty and cognitive impairment. Methods: This study included a total of 7525 Chinese older adults from the 2017–2018 wave of the Chinese Longitudinal Healthy Longevity Survey (CLHLS). Mediation analyses and moderated mediation effect analysis fully adjusted for all potential confounding factors were conducted. Results: Significant correlations were found between frailty, depression, social relationships, and cognitive function. Depression partially mediated the association of frailty with cognitive function [B = −0.198; 95 % confidence interval (CI): (−0.258, −0.143)]. Social relationships moderated the effect of frailty on cognitive function through both path b (depression–cognitive function) [B = 0.137; 95 % CI: (0.045, 0.230)], and path c’ (frailty–cognitive function) [B = 0.870; 95 % CI: (0.562, 1.178)]. In addition, social activities and social networks moderated both the direct and indirect effect of the moderated mediation model. Social support only moderated the direct effect. Limitations: The cross-sectional design of this study precludes any conclusion from the results as to the causality of cognitive impairment. Conclusions: Social relationships moderated both the direct and indirect effects of depressive symptoms on the association between frailty and cognitive impairment. The findings suggest that interventions, such as paying attention to the mental health of old people and improving the quality of social relationships, may help break the link between frailty and cognitive impairment.