Sarcopenia index based on serum creatinine and cystatin C is associated with the risk of stroke in middle-aged and older adults in Chinese: a prospective cohort study from the China health and retirement longitudinal study

The sarcopenia index (SI), calculated as the serum creatinine divided by the serum cystatin C, multiplied by 100, is recommended for predicting sarcopenia. However, limited evidence exists regarding its association with incident stroke. The aim of this study was to assess the relationship between SI and the risk of stroke in middle-aged and older adults. This study utilized a prospective cohort design, enrolling 7842 participants who met the inclusion criteria from the China Health and Retirement Longitudinal Study (CHARLS) between 2011 and 2012. The study utilized the Cox proportional-hazards regression model to investigate the correlation between baseline SI and the risk of stroke. To identify the non-linear relationship between SI and stroke, a Cox proportional hazards regression with cubic spline function and smooth curve fitting technique was employed. Additionally, various sensitivity and subgroup analyses were performed. The mean age of the participants was 59.97 ± 10.06 years, with 3607 (46.0%) being male. The average baseline SI was 78.53 ± 17.43. Over a median follow-up period of 9.0 years, 938 (11.96%) individuals experienced a stroke. The multivariate Cox proportional hazards regression model revealed a negative association between SI and stroke risk (HR = 0.995, 95% CI: 0.990–0.999). A non-linear relationship between SI and incident stroke was identified, with an inflection point at 70.0 for SI. Each 1 unit increase in SI to the right of the inflection point corresponded to a 1.1% decrease in stroke risk (HR = 0.989, 95% CI: 0.983–0.995). However, when the SI was lower than 70.0, the connection was not significant (HR: 1.006, 95% CI: 0.995–1.018). The robustness of our results was confirmed through sensitivity and subgroup analyses. This study provides evidence of a negative and non-linear correlation between SI and stroke risk in middle-aged and older adults in China. When the SI exceeded 70.0, a significant negative association with stroke risk was observed. Maintaining an SI level above 70.0 may contribute to a notable reduction in the risk of stroke.