Because the body produces most of its vitamin D intrinsically following exposure to sunlight, anyone who spends time indoors or in regions of the globe further from the equator exposed to low amounts of sunlight year-round is at risk of becoming vitamin D deficient without proper dietary changes. Approximately 10% of adults in the U.S. are vitamin D deficient, with certain demographic subgroups experiencing higher rates.
A study published in the journal Nutrients, which was conducted by George Mason University in Fairfax, Virginia, and the Mayo Clinic in Onalaska, Wisconsin, assessed vitamin D status among basketball players from the George Mason Patriots men’s and women’s basketball teams.
During the 2018-2019 season, players were either allocated a high dose, low dose, or no dose of vitamin D, depending on the level of vitamin D present in their blood at the beginning of the study with the objective to identify the dosage of vitamin D3 supplementation required for optimal status.
Vitamin D is necessary for maintaining healthy bones, and without it, bones can become soft, thin, and brittle. This can lead to medical issues later in life including osteoporosis, as well as certain types of cancer. Severe vitamin D deficiency is also correlated with cardiovascular disease, cognitive impairment in older adults, and severe asthma in children.
“Many athletes are now engaging in supplementation and we don’t currently know what the optimal or safe amount of supplementation may be,” Dr. Sina Gallo, assistant professor in Mason's Department of Nutrition and Food Studies, said. “Prior studies that have addressed this topic typically report data from non-athletic, older populations. Because athletes may not get the necessary vitamin D through natural dietary sources, supplementation offers a safe, affordable, efficacious method to combat deficiencies. This may be particularly beneficial for athletes living at higher latitudes during the winter months.”
Players were monitored regularly, and compliance to supplementation was assessed by athletic trainers designated to each team. Each player’s body composition, skin pigmentation, sun exposure, dietary intake, and blood were collected during the study to compound other variables.
“Overall, our findings showed that 13 of the 20 (65%) participants were vitamin D insufficient at baseline,” Dr. Margaret Jones, professor in Mason's School of Kinesiology and sport scientist for the Frank Pettrone Center for Sports Performance, said. “This result is consistent with a recent systematic review and meta-analysis wherein 56% of a total sample of 2,000 athletes residing in nine different countries including the United States had inadequate levels of vitamin D.”
Students with darker skin pigmentation exhibited heightened risk of vitamin D insufficiency at baseline, and none of the participants with fair or very fair skin fell into the insufficient category at baseline.
“Albeit a pilot study with a small sample size to derive from, the current results provide further evidence of the high prevalence of vitamin D insufficiency among a sample of highly-trained, NCAA-DI basketball athletes,” Dr. Andrew Jagim, Sport Medicine Research, Mayo Clinic Health System, said. “We, as authors, agree that a larger sample is warranted to aid in the development of screening protocols which will enable medical and sports nutrition staff around the country to identify key risk factors of athletes becoming vitamin D deficient.”