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Vitamin D regulates over 900 genes in the body that affect the immune, musculoskeletal, and endocrine systems, among others. Previous research has shown that vitamin D deficiency may decrease athletic performance. A study published in early 2020 in soccer players demonstrates the importance of maintaining year-round adequate vitamin D levels for athletes.

Estimates suggest that 60 percent of outdoor and 64 percent of indoor athletes may have insufficient vitamin D levels (defined as less than 30 ng/ml), which may impair aerobic capacity and muscle recovery. High-dose supplementation of 5,000 IUs per day has been associated with increased vertical jump height and decreased sprint times.

Twenty-eight professional soccer players completed the study, which took place in three stages from January to September. In January, all players completed 10 days of sun exposure while training in Cyprus (latitude of 34 degrees north, 33 degrees east). Next, half of the players consumed 6,000 IU of vitamin D per day for 6 weeks and half consumed a placebo. In September at the end of the season, the researchers measured changes in serum vitamin D, serum testosterone, body composition, sprint times, and leg power compared to January.

The authors reported that both sun exposure and supplementation increased serum vitamin D levels, serum testosterone levels, and muscle mass, and decreased 5-meter sprint times. However, they noted that most players did not achieve high levels of vitamin D (greater than 50 ng/ml) by September, which may have affected their results.

The authors concluded that vitamin D insufficiency is a problem among athletes, even following summer sun exposure at southern latitudes. They recommended year-round supplementation to support optimal vitamin D status and maximize athletic performance.

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