Effects of vitamin d on muscle function and performance: a review of evidence from randomized controlled trials

Vitamin D insufficiency is frequent in the general population. Meta-analyses of randomized controlled trials (RCTs) have shown a decreased risk of falls in elderly treated with vitamin D supplements, which may be due to an improved neuromuscular function in vitamin D-replete subjects. In most observational studies, vitamin D status correlates positively with muscle strength and postural stability. However, as physical activity is associated with vitamin D status as well as muscle strength, effects of vitamin D status on muscular health can only be assessed properly in RCTs. A systematic search was performed and 16 RCTs on the effects of treatment with vitamin D on muscle function were identified. All except one of the studies were performed in subjects above 50 years of age. Baseline 25-hydroxyvitmin D (25OHD) levels were below 50 nmol/l in 11 studies. Plasma 25OHD levels increased significantly in all studies. In seven studies, a beneficial effect of vitamin D treatment was documented on muscle strength of the lower legs, body sway, and/or physical performance. Identified studies were heterogeneous with regard to most aspects including indices measured. No obvious characteristics delineated studies showing beneficial effects from studies showing no effects. Only a few investigators reported the statistical power of measurements performed. In conclusion, evidence from RCTs do support an effect of vitamin D supplements on muscle strength and function in the elderly, but more studies showing a lack of an effect have been published than studies showing beneficial effects. There is a major lack of data on possible effects in younger subjects.