Relationship between cystatin c levels and risk of frailty in two Chinese populations aged 45~65 years and 65 years or older

Objective To investigate the relationship between serum cystatin C levels and the risk of frailty in different age groups in China.Methods Data from the 2011 China Health and Retirement Longitudinal Study (CHARLS) were used in this study to assess the association between CysC levels and risk of frailty in two Chinese age groups, 45~65 years and ≥65 years. Frailty status was assessed based on the frailty index, and frailty was defined as FI ≥ 25 (range 0~100).The 32 deficits included in the FI were collected through a questionnaire, including the respondent's disease condition, ability to perform daily activities, cognitive function, and self-health status. The relationship between CysC levels and the risk of frailty was analyzed using multivariate logistic regression models and restricted cubic spline in two populations aged 45-65 years and aged ≥65 years.Results A total of 6941 adults aged 45 years and older, with a mean age of 58.3 ± 9.6 years, 49.6% of whom were men, were included in this study, with a total of 1004 (14.5%) experiencing frailty. After adjusting for confounders, compared with the low‑level group (CysC<0.9 mg/L), the OR (95%CI) value of the high‑level group (CysC>1.05 mg/L) was2.13 (1.75 to 2.6). In addition, subgroup analyses showed that the OR (95% CI) between CysC levels and the risk of frailty were (OR, 2.6; 95% CI, 1.72-3.94) and (OR, 1.24; 95% CI, 0.88-1.76) in people aged 45-65 years and people aged ≥65 years, respectively. Restricted cubic spline function analysis showed that CysC levels were approximately "j" shaped in relation to the risk of frailty in 45~65 years old population.Conclusion Higher CysC levels tend to accelerate the progression of frailty in the middle-aged group of 45-65 years old in China, with a "j" curve relationship between them.