Activated vitamin D (calcitriol) is a pluripotent pleiotropic secosteroid hormone. As a steroid hormone, which regulates more than 1000 vitamin D-responsive human genes, calcitriol may influence athletic performance. Recent research indicates that intracellular calcitriol levels in numerous human tissues, including nerve and muscle tissue, are increased when inputs of its substrate, the prehormone vitamin D, are increased.
We 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 25-hydroxy-vitamin D [25(OH)D] levels peak, declines as they decline, and reaches its nadir when 25(OH)D levels are at their lowest. Vitamin D also increases the size and number of Type II (fast twitch) muscle fibers. Most cross-sectional studies show that 25(OH)D levels are directly associated with musculoskeletal performance in older individuals. Most randomized controlled trials, again mostly in older individuals, show that vitamin D improves physical performance.
Vitamin D may improve athletic performance in vitamin D-deficient athletes. Peak athletic performance may occur when 25(OH)D levels approach those obtained by natural, full-body, summer sun exposure, which is at least 50 ng·mL−1. Such 25(OH)D levels may also protect the athlete from several acute and chronic medical conditions.
1Atascadero State Hospital, Atascadero, CA; 2Departments of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC; 3sunlightandhealth.org, Saint George, UT; 4Departments of Orthopedics and Sports Medicine, University of North Carolina, Chapel Hill, NC; and 5Departments of Public Health and Nutrition, University of North Carolina, Chapel Hill, NC
Address for correspondence: John J. Cannell, M.D., Atascadero State Hospital, 10333 El Camino Real, Atascadero, CA 93422; E-mail: firstname.lastname@example.org.
Submitted for publication August 2008.
Accepted for publication October 2008.