Vitamin D and Muscle Function in a Diverse Hemodialysis Cohort.

Background: Declines in skeletal muscle function and widespread vitamin D deficiency are common in individuals receiving hemodialysis (HD), yet the relationships among serum 25-hydroxyvitamin D (25(OH)D) concentrations, vitamin D supplementation, and muscle strength remain incompletely characterized in this population.

Objective: To evaluate the associations between serum 25(OH)D concentrations, dietary vitamin D intake, supplementation status, and muscle strength in a multiethnic cohort of patients undergoing HD.

Design: Cross-sectional study.

Setting: Two satellite HD centers in Toronto, Canada.

Participants: Eighty-one adults receiving HD (mean age 58 years; 64% male) were enrolled following screening based on clinical and demographic inclusion and exclusion criteria.

Measurements: Handgrip strength, measured via digital dynamometry, was the primary outcome and marker of muscle function. Serum 25(OH)D was quantified to assess biochemical vitamin D status. Three-day food and supplement logs were used to estimate dietary vitamin D intake and supplementation. Associations were assessed using multivariable linear and logistic regression, adjusting for age, sex, and dry weight.

Results: Forty-seven percent of participants exhibited sex-specific weak handgrip strength, and 25% were vitamin D deficient (<27.5 nmol/L). Serum 25(OH)D concentrations were positively associated with handgrip strength (r = 0.298, P = .023), and vitamin D supplementation was similarly associated (r = 0.285, P = .025). Deficient serum 25(OH)D levels were associated with over five-fold increased odds of weak grip strength (odds ratio (OR) 5.33; 95% confidence interval (CI): 1.59-20.67; P = .009). Although dietary vitamin D intake was inadequate in 97% of participants, it was not independently associated with muscle strength. Participants who reported supplement use had significantly higher mean serum 25(OH)D concentrations than those who did not supplement.

Limitations: This study's cross-sectional design and single geographic setting limit causal inference and broader generalizability. Self-reported dietary intake may be subject to recall error.

Conclusions: Biochemically defined vitamin D deficiency and absence of vitamin D supplementation were associated with reduced muscle strength in patients receiving HD. These findings suggest that higher serum 25(OH)D concentrations may support better musculoskeletal function, in addition to other known benefits of higher serum vitamin D levels, in populations undergoing HD treatment.