Background/Purpose: Currently, there is growing evidence that vitamin D plays a role on several tissues including skeletal muscle. Previous studies suggested that vitamin D deficiency is associated with low muscular strength. The objective of this meta-analysis is to summarize the effects of vitamin D supplementation on muscle strength.

Methods: A systematic research of randomized controlled trials (RCTs), performed between 1966 and February 2013, assessing the effect of vitamin D supplementation on muscle strength has been conducted by two independent reviewers (data sources: Medline, Cochrane Database of Systematics Reviews, Cochrane Central Register of Controlled Trials, manual review of the literature and congressional abstracts). All forms and doses of vitamin D supplementation, with or without calcium supplementation, compared with placebo or control were included. Muscle strength was assessed either by grip strength and/or lower limb muscle strength. The quality of the RCTs was evaluated using the Jadad criteria.

Results: Out of the 214 potentially relevant articles, 19 RCTs involving 4824 individuals (mean age: 66.0 years) met the inclusion criteria. Studies show a mean quality score of 3.8/5 points. Results reveal a significant positive effect of vitamin D supplementation on global muscle strength (Figure) with a standardized mean difference (SMD) of 0.096 (95% CI=0.007-0.184; p=0.034). No significant between-study heterogeneity is found (Q-value= 23.6; p= 0.21; I²= 19.6%). No publication bias was observed as shown with the Egger’s regression analysis (p=0.13). Regarding the individual type of strength, 13 studies assessed the effect of vitamin D supplementation on grip strength and 15 on lower limb muscle strength. Results show no significant effect of vitamin D supplementation on grip strength (SMD=0.062, p=0.264), but a significant positive effect on lower limb muscle strength (SMD=0.169, p=0.03).

Figure: Forest plot for summary standardized mean difference for global muscle strength

Conclusion: Based on the studies included in this meta-analysis, vitamin D supplementation has a positive impact on global muscle strength, and more especially, on lower limb muscle strength.