Serum levels between 40-50 ng/ml is 'sweet spot' for athletes
Vitamin D is an essential nutrient for calcium homeostasis and the expression of hundreds of genes. Sufficient serum levels of vitamin D are required, not only for proper bone mineralization but for a host of other factors in musculoskeletal system structure and function.

Despite the wide variety of vitamin D sources, whether synthesized in response to natural sunlight or ingested in one of many formulations, such as pills, chewable gummies, sprays, liquids, and even chocolates, most of the population is vitamin D deficient. Among other factors, this deficiency can be attributed to geography (areas with less sunlight and direct UVB rays), lifestyle (spending a lot of time indoors), diet, and genetics.

Although vitamin D deficiency can affect anyone, it is worth examining how a dramatic deficiency can impact athletes, as the demands on their musculoskeletal system are much greater.

Previous studies have shown that 30 ng/ml is the threshold of serum vitamin D concentration to support proper mineralization of non-mineralized bone matrix. Vitamin D concentrations above 40 mg/ml exhibit a protective effect against stress fractures. Some have speculated that levels above 50 ng/ml were needed for optimal physical performance.

In their review, Shuler et al reported that increasing levels of vitamin D, up to 50 ng/mL, reduced inflammation, pain, and myopathy, while increasing muscle protein synthesis, adenosine triphosphate concentration, strength, jump height, jump velocity/power, exercise capacity, and physical performance.

There are myriad reasons why vitamin D could be so pivotal to achieving maximal physical performance. One of the more enticing reasons is that it directly affects the number of Type IIA muscle cells. Type II, or fast-twitch muscle fibers, are used for explosive physical activity, such as lifting weights and sprinting. These fibers also atrophy with aging and underuse, especially in larger muscle groups such as the upper legs and back. This scenario makes an even more compelling case for vitamin D supplementation, especially in athletes and aging individuals.

A lifestyle balancing act
As a potent secosteroid, however, vitamin D supplementation comes with risks. In fact, many consider the term "vitamin" to be a misnomer because its function is that of a hormone that has profound effects on multiple physiologic pathways, especially calcium regulation. Supplements may be mislabeled, misformulated, and overprescribed to consumers, leading to hypercalcemia and other side effects.

When speaking specifically of the athletic population, risk of overdose becomes even more of a concern, as athletes strive to make sure their bodies are performing at peak condition. Highly motivated athletes could easily find themselves oversupplementing in an effort to maximize the benefits of vitamin D. Side effects of vitamin D overdose, mostly related to hypercalcemia, include soft tissue calcification, which is especially troublesome in the heart, kidneys, and bowels. In these cases, blood pressure dysregulation, electrolyte imbalances, dehydration, constipation, and arteriolar hardening may result. Due to its fat solubility, vitamin D remains in tissues for an extended period of time. Therefore, vitamin D overdose can take months to become symptomatic and treatment of overdose can be a lengthy process.

These studies suggest athletes should have their vitamin D levels tested and maintain supplementation regimens to keep their serum levels between 40–50 ng/ml to gain all potential benefits of vitamin D, while preventing the chance of any side effects coming from overconsumption. Athletes should be thoroughly educated about the use of any and all external supplementation, and their regimens should be strict and supervised.

For the nonathlete (someone not engaged in strenuous exercise more than 2 to 3 times per week) and nonelderly, vitamin D testing may not be necessary. Blue Cross Blue Shield published an analysis that showed only 1 out of 10 New York residents were at risk of vitamin D deficiency-related health issues, and that 9 out of 10 people who were tested received test results that had no effect on the course of their treatment (whether they had a starting lab value or not).

A vitamin D level test can cost about $50 with some insurance providers, while other insurers may not cover it at all. Most healthcare providers and nutrition experts would agree that the average person should simply take a standard, low-dose vitamin D supplement. Serum concentration testing may be helpful in athletes or in those at increased risk of deficiency.

Sumeet Jindal, MD, MBA, is completing a transitional year at HCA Grand Strand Medical Center.

Scott F.M. Duncan, MD, MPH, MBA, is director of orthopaedic surgery graduate medical education at HCA Grand Strand Medical Center.

Graphic (PDF)
Studies suggest athletes should test their vitamin D levels and maintain supplementation regimens to keep their serum levels between 40-50 ng/ml to gain all potential benefits of vitamin D, while preventing the chance of any side effects coming from overconsumption.
Courtesy of Sumeet Jindal, MD, MBA, and Scott F.M. Duncan, MD, MPH, MBA

Bottom Line

• The majority of the population is vitamin D deficient. Recommended vitamin D serum levels differ based on lifestyle.
• Serum levels between 40-50 ng/ml is 'sweet spot' for athletes.
• The elderly, who experience decreases in bone mass, have different needs.
• The need for serum level testing should be discussed with healthcare providers.

References

1. Larson-Meyer, D. Enette, and Kentz S. Willis. "Vitamin D and athletes." Current sports medicine reports 9.4 (2010): 220-226.
2. Lips, Paul, et al. "Vitamin D Supplementation and Fracture Incidence in Elderly PersonsA Randomized, Placebo-Controlled Clinical Trial." Annals of Internal Medicine 124.4 (1996): 400-406.
3. Ogan, Dana, and Kelly Pritchett. "Vitamin D and the athlete: risks, recommendations, and benefits." Nutrients 5.6 (2013): 1856-1868.
4. Vieth, Reinhold. "Vitamin D supplementation, 25-hydroxyvitamin D concentrations, and safety." The American journal of clinical nutrition 69.5 (1999): 842-856.
5. Weight, Lindsay M., et al. "Vitamin and mineral status of trained athletes including the effects of supplementation." The American journal of clinical nutrition 47.2 (1988): 186-191.