Vitamin D is a crucial nutrient for athletes, playing a significant role in calcium and bone health. It's absorbed through the skin from sunlight or from diet and then metabolized into its active form. This active form is essential for regulating calcium and phosphorus homeostasis, supporting skeletal muscle function, modulating the immune system, and influencing gene regulation. Vitamin D deficiency can be detrimental to an athlete's performance and overall health. A protocol for vitamin D supplementation in athletes is a topic of growing interest. We recently published an in depth review on Vitamin D in Orthopedics.
Defining and Detecting Vitamin D Deficiency
Most sources recommend that athletes maintain vitamin D levels equal to or greater than 40 ng/mL. Athletes should aim for higher than this number and consult with their physician about getting a blood test to check their levels. This simple step can help determine if supplementation is necessary.
Prevalence and Risk Factors
Vitamin D insufficiency is common, affecting about 40% of the general U.S. population. This rate is estimated to be even higher among athletes, at approximately 50%. A primary reason for this higher prevalence is that many athletes train indoors, limiting their exposure to sunlight, the main source of vitamin D. This issue is compounded for athletes whose peak training season occurs during winter and early spring.
Another significant risk factor for vitamin D deficiency is race and skin pigmentation. A study on a single NFL team found that Black players had significantly lower vitamin D levels than their white teammates. The study also revealed that every player classified as deficient was Black. This is because higher levels of melanin, the pigment that gives skin its color, reduce the amount of UVB radiation that reaches the deeper layers of the skin. This, in turn, decreases the skin's ability to produce vitamin D.
Additional risk factors include:
- High Latitude: Athletes living and training in higher latitudes are at increased risk due to weaker UVB rays.
- Winter Sports: Training during seasons with reduced sun exposure.
- Previous Fracture History: A history of fractures may indicate underlying issues with bone health.
Why It Matters for Athletes
Maintaining adequate vitamin D levels is critical for several reasons:
- Bone Health: Low vitamin D levels can lead to increased bone turnover, significantly raising the risk of fractures.
- Muscle Function: Vitamin D receptors influence muscle fiber growth, and low levels can contribute to muscle weakness. A study has shown that players with a history of lower extremity muscle strain and core muscle injury had a higher prevalence of inadequate Vitamin D.
- Immune System: Vitamin D affects both the innate and adaptive immune systems, which are crucial for fighting off infections. Low levels have been linked to an increased risk of respiratory illnesses, which can disrupt training and increase injury risk.
Conclusion
Given the high prevalence of deficiency and its potential negative impact on performance, vitamin D levels should be screened in all athletes. The American College of Sports Medicine (ACSM) recommends vitamin D supplementation for athletes with high-risk factors or low lab values. Most athletes should consider taking a supplement, especially if they have risk factors like significant indoor training, a history of fractures, or darker skin pigmentation.
Please consult with a board-certified physician to discuss whether vitamin D supplementation is right for you.
