Supplementary Material for: Association between Vitamin D Level and Muscle Strength in Patients Undergoing Hemodialysis

<b><i>Introduction:</i></b> Identification of the risk factors and treatment of the decrease in muscle mass or strength are important to improve the prognosis of patients undergoing hemodialysis (HD). Previous studies have investigated the association between vitamin D level and muscle mass or strength in patients undergoing HD. However, there are conflicting results regarding this association. <b><i>Objective:</i></b> To evaluate the association between vitamin D level and muscle mass indices, strength, or physical performance in patients undergoing HD. <b><i>Methods:</i></b> This study was performed in a tertiary medical center. We included patients undergoing HD aged ≥20 years. A total of 84 patients were enrolled. The patients were divided into tertiles based on the 25-hydroxy (25-OH) vitamin D level as follows: lowest tertile (Lowest T, <i>n</i> = 28), middle tertile (Middle T, <i>n</i> = 28), and highest tertile (Highest T, <i>n</i> = 28). We evaluated the association between the tertiles and clinical outcomes including nutritional status, muscle mass, muscle function, handgrip strength (HGS), physical performance, and health-related quality of life (HRQoL) scales. <b><i>Results:</i></b> There were no significant differences in the muscle mass indices and nutritional markers according to tertiles of 25-OH vitamin D level. However, 25-OH vitamin D level as a continuous variable or the tertile of 25-OH vitamin D level as a categorical variable was positively associated with HGS. Logistic and linear regression analyses showed a consistent superiority of the Highest T in HGS compared with the Lowest or Middle T. Although the statistical significance was weak, the scores of various physical performance tests and the HRQoL scales were highest in the Highest T among the 3 tertiles. <b><i>Conclusion:</i></b> The present study demonstrated that serum vitamin D level is associated with HGS in patients undergoing HD regardless of muscle mass indices or nutritional status.