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 To summarize with a meta-analyse 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=0.02). No significant effect was found on muscle mass (SMD 0.058; p=0.52) or muscle power (SMD 0.057; p=0.657). 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 versus 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.