Caitlin Hendler, M.S.
Most commonly known as the “Sunshine Vitamin,” the main source of this fat-soluble vitamin is exposure to sunlight because of few food sources. The benefits of vitamin D go much further than merely a bronze tan – studies show that it assists in growth, remodeling, regulation of calcium and phosphate concentrations for ideal bone health and physical performance. Vitamin D is a vital nutrient for optimal health in the general population but even more significantly for athletes.
Deficiency
Vitamin D deficiency occurs when the intake is lower than the recommended values, which leads to chronic substrate starvation due to the immediate uptake of vitamin D for metabolic needs. The recommended daily allowance (RDA) for vitamin D is 600 IU and in simpler terms, sensible sun exposure to maintain sufficient amounts of vitamin D is defined as 5-10 minutes of exposure on the main body parts. To test for vitamin D deficiency, the serum total 25-hydroxyvitamin D (25(OH) D) level is measured from a blood test. Vitamin D deficiency is most often defined as a total 25(OH) D level of less than 20 ng/mL. Vitamin D 
deficiency can be connected to other health complications, with an increased risk for hypertension, cardiovascular disease, different cancers and more. Production of vitamin D is subject to change, depending on individual and environmental factors. Specific groups are more at risk for vitamin D deficiency such as breast-fed infants, older adults, those with limited sun exposure and people with darker skin. Breast-fed infants rely on the mother’s vitamin D status where as older and people with dark skin have a harder time synthesizing or producing vitamin D.
Athletes and Vitamin D
Athletes are particular about hydration, their equipment and even certain superstitions to ensure that they perform to their peak ability. Nevertheless, sometimes athletes may overlook aspects of their nutrition. Recent studies have shown vitamin D deficiency in the athletes studied. The most probable reason for poor vitamin D status is an insufficient endogenous synthesis from sunlight. An adequate amount of time in the sun has been defined as 5-10 minutes of exposure on the arms and legs for two to three times a week. From that, one might assume that only indoor sports are at risk and that outdoor sports surely get enough sunlight exposure, but that is not always the case. Skin pigmentation, early or late-day training, indoor training, and geographic location can cause impaired synthesis of vitamin D. Athletes limit their vitamin D intake when scheduling their training sessions in the evening hours, and wearing equipment that does not allow their skin to be exposed to sunlight.
Athletic Performance
Muscle performance, strength and power in correlation with vitamin D has been studied over the recent years verifying that overall muscle performance is affected when the individual has an impaired vitamin D status. Studies testing before and after vitamin D treatment in vitamin deficient subjects illustrate an increase in the number and diameter of fast, Type 2 muscle fibers when analyzing specific muscle biopsies (1). Furthermore, jump height, velocity and power is affected by low vitamin D status (3). Vitamin D helps regulate the calcium absorption with studies showing a lower incidence of stress fractures. Overall vitamin D is essential and an important part of an athletes diet. With their increased significance on muscle performance and overall health, vitamin D RDA has been suggested at 800-2200 IU (2).
Further Reading:
- Cannell JJ, Hollis BW, Sorenson TB, Taft TN, Anerson JJ. Athletic Performance and vitamin D. Med. Sci. Sports Exer. 2009; 41:1102-10. http://www.ncbi.nlm.nih.gov/pubmed/19346976
- Larson-Meyer, DE & Willis KS. Vitamin D and athletes. Curr. Sports Med. Rep., Vol. 9, No. 4, pp.220-226, 2010. http://www.ncbi.nlm.nih.gov/pubmed/20622540
- Ward KA, Das G, Berry JL, et al. Vitamin D status and muscle function in post-menarchal adolescent girls. J. Clin. Endocrinol. Metab. 2009; 94:559-63. http://press.endocrine.org/doi/pdf/10.1210/jc.2008-1284