In April 2019 researchers from China published their review of the medical scientific literature to assess the effect of vitamin D supplementation on skeletal muscle strength and muscle power of athletes. A total of 8 studies involving 284 athletes were included. The methods used to assess the muscle strength were inconsistent across the studies and muscle power was assessed via vertical jump tests. Results showed that vitamin D supplementation had no effect on overall muscle strength outcomes. However, a further analysis revealed that vitamin D supplementation had an effect on lower-limb muscle strength but not upper-limb muscle strength or muscle power. It was also seen that vitamin D supplementation was more effective for athletes trained indoors.
Zhang L et al. Effect of vitamin D supplementation on upper and lower limb muscle strength and muscle power in athletes: A meta-analysis. PLoS One. 2019 Apr 30;14(4):e0215826.