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Vitamin D is an essential nutrient that is involved in multiple physiological processes. Inadequate vitamin D status is associated with poor bone health, impaired immune function, and increased risk for depression. Approximately 70 percent of people living in the United States are vitamin D deficient. A recent study found that athletes who participate in indoor sports may be at high risk for vitamin D deficiency.

Although vitamin D is available in small quantities in food, the primary source of vitamin D is via endogenous synthesis. This process occurs in a stepwise manner that starts in the skin following exposure to ultraviolet light and continues in the liver and kidneys, where the vitamin’s active form is made. Since ultraviolet light is required for vitamin D synthesis, reduced exposure to the sun or having dark-colored skin impairs vitamin D production. Plasma concentrations of vitamin D are considered optimal at 50 ng/mL or above; sufficient at 30 ng/mL to 50 ng/mL; and insufficient at less than 30 ng/mL.

The study involved 20 male and female collegiate basketball players (average age, 20 years) of varied races and ethnicities. The majority of the players (60 percent) self-reported as African American. The authors of the study collected blood samples to determine the players' vitamin D status, assessed their body composition, and measured their skin pigmentation. The participants completed questionnaires about their sun exposure, winter travel to sunny locations, and sunscreen use.

Then the authors allocated the players to receive one of three daily doses of vitamin D for five months, based on whether their vitamin D status was optimal (no supplementation), sufficient (5,000 IU), or insufficient (10,000 IU). Two of the participants had vitamin D concentrations in the optimal range, five in the sufficient range, and 13 in the insufficient range. More than 90 percent of those identified as insufficient had dark or olive skin tone.

At the end of the five-month study period, one of the athletes in the non-supplemented group remained in the optimal range but the other athlete dropped to the sufficient range. Of the athletes taking the 5000 IU dose, 75 percent remained in the sufficient range, but 25 percent dropped to the insufficient range. Of those taking the 10,000 IU dose, 23 percent remained in the insufficient range, 69 percent moved into the sufficient range, and one moved into the optimal range.

These findings suggest that collegiate athletes who play indoor sports may be at risk for vitamin D deficiency. Furthermore, high dose supplementation with 10,000 IU of vitamin D daily may be beneficial in improving vitamin D status for most players, but it falls short for some.

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