Vitamin D and calcium are essential parts of all diets. Both are important in bone health, but are also important in other functions of the athlete’s body that optimize performance. Vitamin D helps with absorption of calcium, iron, magnesium and zinc. Deficiency in Vitamin D may increase fracture risk, and may cause vague, diffuse muscle and bone aches and pains. Calcium is also important in maintaining proper muscle and nervous system functioning.
Vitamin D is actually not a true vitamin; rather it is a precursor of a hormone, which means that daily intake is needed to sustain normal levels of it in the body. The American Academy of Pediatrics recommends 400 IU/day of Vitamin D for infants through adolescents. However, some individuals, including females, those taking certain medications and those with darker skin or low exposure to sunlight, may benefit from higher levels. In those cases, 1500-2000 IU/day may be needed to keep the usable Vitamin D at normal levels.
Sources of Vitamin D include sunlight, foods and supplements. Generally, 15-30 minutes of unprotected sun exposure two to four times per week will maintain adequate levels of Vitamin D. Foods rich in Vitamin D are listed in the following chart. Vegetarian diets can be deficient in Vitamin D if they do not incorporate fortified food choices.
* Medications that can lower Vitamin D levels:
• Anti-seizure medicines (e.g., phenytoin)
• Glucocorticoids (steroids)
• Anti-fungal medicines (e.g., oral ketoconazole)
Vitamin D toxicity is possible after large doses of supplements, but toxicity is not possible by sun exposure, as any excess created by photoconversion at the skin level will change to inactive metabolites.
Up to about 30 years of age, bone size and bone mass increase rapidly. The greatest deposition of total bone mineral occurs during puberty. Unfortunately, it has been shown that more than 50 percent of boys ages 9-13 and girls ages 9-18 have inadequate intake levels of calcium. The recommended amount for both males and females ages 9-18 years is 1300 mg/day. Calcium is often coupled with Vitamin D in order to enhance its absorption.
Calcium intake from food sources is preferable, but if supplementation is necessary, the type of calcium and amount of elemental calcium absorbed at one time are important to consider. Calcium carbonate is most commonly available and is best absorbed when stomach acid is present; i.e., when you are eating. Calcium citrate is absorbed without the need for stomach acid and is less constipating. The amount of calcium in each type of supplement varies, so reading the label is important. The amount of calcium absorbed is greatest when doses are 500mg or less. Calcium toxicity can occur and may lead to kidney stone formation.
High school athletes and children benefit from combining calcium with Vitamin D in order to obtain optimal health and reduce fracture risk, including stress fractures. The recommended allowances for Vitamin D and calcium should ideally be met with dietary intake – not supplements. These guidelines may need to be adjusted depending on individual demands, as well as certain medications and medical conditions. It is highly recommended that young athletes consult their physicians for additional advice to discuss any special circumstances, or if they are considering dietary supplementation.
Committee to Review Dietary Reference Intakes for Vitamin D and Calcium, VNB Institute of Medicine. Dietary Reference intakes for Calcium and Vitamin D. Washington, DC: National Academy Press; 2010.
Casey C, Slawson DC, Neal LR. Vitamin D Supplementation in Infants, Children, and Adolescents. Am Fam Physician. 2010;81(6):745-48.
Li K, Kaaks R, et al. Associations of dietary calcium intake and calcium supplementation with myocardial infarction and stroke risk and overall cardiovascular mortality in the Heidelberg cohort of the European Prospective Investigation into Cancer and Nutrition study (EPIC-Heidelberg). Heart. 2012;98(12)920-925.
Matkovic V, Jelic T, Wardlaw GM, et al. Timing of peak bone mass in Caucasian females and its implication for the prevention of osteoporosis. Inference from a cross-sectional model. J Clin Invest 1994; 93:799.
Bailey RL, Dodd KW, Goldman JA, Gahche JJ, Dwyer JT, Moshfegh AJ, Sempos CT, Picciano MF. Estimation of total usual calcium and vitamin D intakes in the United States. J Nutr. 2010 Apr;140(4):817-22.
Katherine L. Dec, M.D., is a physician at CJW Sports Medicine in Richmond, Virginia. She is chair of the Virginia High School League Sports Medicine Committee and member of the NFHS Sports Medicine Advisory Committee. Cindy J. Chang, M.D., has been the head team physician at the University of California, Berkeley and was chief medical officer for Team USA at the London Olympics. She is a member of the NFHS Sports Medicine Advisory Committee.