Association Between Muscle Strength and Cystatin C-Based Estimated Glomerular Filtration Rate Among Middle-Aged and Elderly Population: Findings Based on the China Health and Retirement Longitudinal Study (CHARLS), 2015

Background: Patients with chronic kidney disease (CKD) are prone to muscle strength degeneration. However, the relationship between mild-to-moderate renal insufficiency and low muscle strength remains unclear. As cystatin C is not subject to muscular conditions and is a sensitive serum marker in preclinical renal disease, we aimed to investigate the association between estimated glomerular filtration rate (eGFR) based on cystatin C and muscle strength in the Chinese population. Methods: This was a cross-sectional study enrolling 12,398 Chinese participants aged above 45 years (5762 men and 6636 women) from the 2015 China Health and Retirement Longitudinal Study. Handgrip strength (HGS) was used to assess muscle strength. Locally weighted scatterplot smoothing (LOWESS) curves were employed to visualize the relationships between eGFR and HGS. Multivariable logistic regression was conducted to analyze the correlation between kidney function and low muscle strength. Results: Significant differences in HGS by CKD stage were observed in both sexes after adjusting for age and body mass index. LOWESS curves demonstrated concomitant decreases in HGS and kidney function at eGFR levels below 120 mL/min/1.73 m(2) in both sexes. According to multivariate logistic regression, participants with CKD stages 2 (odds ratio [OR]: 1.256, 95% confidence interval [CI]: 1.120-1.409), 3 (OR: 2.725, 95% CI: 2.2585-3.288), and 4-5 (OR: 3.069, 95% CI 1.747-5.392) had higher risk of low muscle strength than those who were normal or had CKD stage 1 after adjusting for demographic and clinical variables. Conclusion: Our study illustrated that CKD stage was independently associated with low muscle strength in Chinese middle-aged and elderly populations.