Association between Abdominal Obesity, Vitamin D Levels and Frailty in Chinese Elder Adults

Background The incidence of frailty among the elderly in China increases with age, investigating the mechanisms by which central obesity and vitamin D levels contribute to the development of frailty is essential for effective management strategies. Objective A cross-lagged model was employed to investigate the longitudinal mediating role of vitamin D levels in the relationship between central obesity and frailty among the elderly, thereby offering a theoretical framework for the management of frailty in this population. Methods The study subjects were 1 364 elderly individuals selected from the Chinese Longitudinal Healthy Longevity Study (CLHLS) in 2011-2012 (T1) and 2014 (T2). The vitamin D levels of the study subjects were measured, and abdominal obesity was assessed using the weight-adjusted-waist index (WWI), while frailty was measured using the frailty index (FI). A cross-lagged model was implemented to analyze the causal temporal relationship and underlying mechanisms between central obesity, vitamin D levels, and frailty among the elderly. Results The detection rate of frailty in the elderly was 21.8% (298/1 364) at T1 and 31.2% (425/1 364) at T2. At two time points, WWI was negatively correlated with vitamin D levels (P<0.05) and positively correlated with FI (P<0.05) ; vitamin D levels were negatively correlated with FI (P<0.05). Cross-lagged model results showed that WWI at T1 could predict FI at T2 (β=1.124, P<0.05), and FI at T1 could predict WWI at T2 (β=0.125, P<0.05). Longitudinal mediation effect analysis showed that T1 WWI could not only directly predict T2 FI (β=0.040, P<0.05), but also predict T2 FI through the mediating effect of T2 vitamin D level (β=-0.131, P<0.05) . Conclusion Abdominal obesity can not only directly predict frailty in the elderly, but also indirectly affect frailty in the elderly through the longitudinal mediating effect of vitamin D levels. Elderly people should regularly monitor abdominal obesity and vitamin D levels, to prevent or delay the onset of debilitation.