Review ArticleEffects of Vitamin D on Skeletal Muscle and Athletic PerformanceAbrams, Geoffrey D. MD; Feldman, David MD; Safran, Marc R. MDAuthor Information From the Department of Orthopaedic Surgery (Dr. Abrams and Dr. Safran) and the Department of Medicine, Division of Endocrinology, Gerontology, and Metabolism (Dr. Feldman), Stanford University School of Medicine, Palo Alto, CA, and VA Palo Alto Healthcare System, Palo Alto (Dr. Abrams). Dr. Abrams or an immediate family member serves as a paid consultant to or is an employee of and has stock or stock options held in Cytonics. Dr. Safran or an immediate family member has received royalties from DJO Global, Smith & Nephew, and Stryker; is a member of a speakers’ bureau or has made paid presentations on behalf of ConMed, Medacta, and Smith & Nephew; serves as a paid consultant to or is an employee of ConMed, Cool Systems, and Medacta; serves as an unpaid consultant to Biomimedica, Cool Systems, DJO Global, Smith & Nephew, and Ferring Pharmaceuticals; has stock or stock options held in Biomimedica, DJO Global, and Smith & Nephew; has received research or institutional support from Ferring Pharmaceuticals and Smith & Nephew; and serves as a board member, owner, officer, or committee member of the International Society of Arthroscopy, Knee Surgery and Orthopaedic Sports Medicine and the International Society for Hip Arthroscopy. Neither Dr. Feldman nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this article. Journal of the American Academy of Orthopaedic Surgeons: April 15, 2018 - Volume 26 - Issue 8 - p 278-285 doi: 10.5435/JAAOS-D-16-00464 Metrics Abstract Vitamin D is known to be important for calcium homeostasis and bone metabolism. It also has important direct effects on skeletal muscle. Unlike authentic vitamins, which cannot be synthesized in the body, vitamin D is produced in the skin using sunlight. Through its nuclear receptor (ie, vitamin D receptor) located throughout the body, including skeletal muscle, vitamin D initiates genomic and nongenomic pathways regulating multiple actions, including myocyte proliferation and growth. In some studies, vitamin D supplementation has been shown to increase muscle strength, particularly in people who are vitamin D deficient. Higher serum levels of vitamin D are associated with reduced injury rates and improved sports performance. In a subset of the population, vitamin D appears to play a role in muscle strength, injury prevention, and sports performance. Copyright 2018 by the American Academy of Orthopaedic Surgeons.