According to a new review of research, evidence suggests that adequate treatment of vitamin D deficient athletes could dramatically improve their performance. Activated vitamin D is a steroid hormone which regulates more than 1000 human genes. Recent research indicates that intracellular vitamin D levels in numerous human tissues, including nerve and muscle tissue, are increased when inputs of its substrate, the prehormone vitamin D, are increased.

Researchers reviewed the world's literature for evidence that vitamin D affects physical and athletic performance. Numerous studies, particularly in the German literature in the 1950s, show vitamin D-producing ultraviolet light improves athletic performance. Furthermore, a consistent literature indicates physical and athletic performance is seasonal; it peaks when vitamin D levels peak, declines as they decline, and reaches its nadir when the  levels are at their lowest.

Vitamin D also increases the size and number of fast twitch muscle fibers. Most cross-sectional and randomized controlled studies show that vitamin D levels are directly associated with musculoskeletal performance.