Association Between Relative Fat Mass and Risk of Cognitive Impairment: The Role of Social Determinants of Health

OBJECTIVE: This study examined the relationship between relative fat mass (RFM) and the risk of new-onset cognitive impairment and tested the mediating effect of social determinants of health (SDOH). METHODS: Data originated from the China Health and Retirement Longitudinal Study. Data from 6147 participants without cognitive impairment at baseline were included. RFM was calculated and categorised into quartiles, whereas a cumulative SDOH score was constructed and grouped into tertiles. The association between RFM and new-onset cognitive impairment was assessed by using Kaplan-Meier curves, multivariable Cox proportional hazards models and restricted cubic splines (with piecewise regression for threshold analysis). Subgroup and joint effect analyses were performed on SDOH and RFM. RESULTS: During a mean follow-up of 7.16 years, 1242 incident cases of cognitive impairment occurred. Elevated RFM was a significant risk factor for cognitive impairment (hazard ratio [HR] = 1.024, 95% confidence interval [CI]: 1.015-1.033, p < 0.001). This correlation was nonlinear, and RFM was estimated to have an inflection point of 26.45. The analysis of interaction effects showed that the risk of cognitive impairment in the population at risk (low SDOH/obesity) was higher by 91% (HR = 1.908, 95% CI: 1.516-2.401, p < 0.001) relative to that in the high SDOH/nonobesity group. Notably, amongst obese individuals, high SDOH/obesity was not associated with a significantly increased risk (HR = 1.047, 95% CI: 0.828-1.325, p = 0.701). CONCLUSIONS: Elevated RFM is significantly associated with an increased risk of cognitive impairment. However, this relationship is moderated by socioeconomic context. Low SDOH is a serious aggravating factor for the risk of high RFM, whereas high SDOH may play a massive buffering and protective role. Intervention approaches should be designed by accounting for personal metabolic factors along with the social environment, with particular attention paid to dually disadvantaged groups to avoid cognitive deterioration.