Vitamin D, also known as the sunshine vitamin is an essential vitamin that plays many important roles in the proper functioning of the body. Though classified as a vitamin, vitamin D is actually a key regulatory hormone for multiple physiological processes. It is estimated that 1 billion people, including the elderly, young adults, athletes and children, are vitamin D deficient or insufficient. The main cause of vitamin D deficiency in the athletic population is the direct result of decreased ultraviolet B (UVB) radiation absorption into the skin, which especially affects indoor athletes and those who live and train in northern latitudes. Adequate vitamin D status is essential for ensuring normal calcium absorption and maintenance of healthy plasma calcium levels.€ Besides bone support, vitamin D has many other roles in the body, including modulation of cell growth, neuromuscular and immune function, and inflammatory support. € Clinical research has shown there is a positive association between Vitamin D 25(OH)D serum concentrations, lower extremity function, proximal muscle strength and physical performance.
Vitamin D deficiency is associated with diffuse muscle pain, muscle weakness predominantly in the proximal muscle groups, and a reduction in performance speed. A serum 25-hydroxyvitamin D level below 50 nmol/l has been associated with increased body sway and a level below 30 nmol/l with decreased muscle strength. Based on the study by Barker et al, pre-exercise serum 25(OH)D concentrations could influence the recovery of skeletal muscle strength after an acute bout of intense exercise. Numerous scientists now feel that supplementation with vitamin D at levels greater than previously thought necessary is critical to helping maintain healthy bone remodeling and healthy vitamin D plasma levels. A committee of the Institute of Medicine reviewed the data on vitamin D needs and concluded that persons are at risk of vitamin D deficiency at serum 25(OH)D concentrations <30 nmol/L (<12 ng/mL), and practically all people are sufficient at levels !50 nmol/L (!20 ng/mL). Vitamin D is fat-soluble, so it should be taken with foods containing fat to aid in absorption through the small intestine. Vitamin D intoxication is extremely rare. Doses of 10,000 IU of vitamin D3 per day for up to 5 months did not cause toxicity. The latest United States recommended dietary allowance (RDA) for vitamin D is 600 IU per day. However, dietary intake may vary for athletes based on diet and intestinal absorption and the amount of sunlight exposure, thereby requiring higher supplemental doses.