The Effects of Vitamin D on Skeletal Muscle Strength, Muscle Mass, and Muscle Power: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

CONTEXT: There is growing evidence that vitamin D plays a role on several tissues including skeletal muscle. OBJECTIVE: The aim was to summarize with a meta-analysis, the effects of vitamin D supplementation on muscle function. DATA SOURCES: A systematic research of randomized controlled trials, performed between 1966 and January 2014 has been conducted on Medline, Cochrane Database of Systematics Reviews, Cochrane Central Register of Controlled and completed by a manual review of the literature and congressional abstracts. STUDY SELECTION: All forms and doses of vitamin D supplementation, with or without calcium supplementation, compared with placebo or control were included. Out of the 225 potentially relevant articles, 30 randomized controlled trials involving 5615 individuals (mean age: 61.1 years) met the inclusion criteria. DATA EXTRACTION: Data were extracted by two independent reviewers. DATA SYNTHESIS: Results revealed a small but significant positive effect of vitamin D supplementation on global muscle strength with a standardized mean difference (SMD) of 0.17 (P = .02). No significant effect was found on muscle mass (SMD 0.058; P = .52) or muscle power (SMD 0.057; P = .657). Results on muscle strength were significantly more important with people who presented a 25-hydroxyvitamin D level <30 nmol/L. Supplementation seems also more effective on people aged 65 years or older compared to younger subjects (SMD 0.25; 95% CI 0.01 to 0.48 vs SMD 0.03; 95% CI -0.08 to 0.14). CONCLUSIONS: Vitamin D supplementation has a small positive impact on muscle strength, but additional studies are needed to define optimal treatment modalities, including dose, mode of administration, and duration.