Vitamin D is essential for the human body, as it regulates the absorption of calcium and phosphorus, which are essential for bone health and muscle function. In athletes, adequate vitamin D levels help improve muscle strength, endurance, and recovery, reducing the risk of stress fractures and injuries. Furthermore, this vitamin plays a key role in the immune system and in modulating inflammation, crucial aspects for those who participate in high-intensity sports.
Vitamin D Metabolites and Intake
Vitamin D occurs in two main forms:
- Vitamin D2 (ergocalciferol): of plant origin, found in some mushrooms and fortified foods.
- Vitamin D3 (cholecalciferol): of animal origin, found in fatty fish (salmon, mackerel), egg yolk, and dairy products. It is also the form synthesized by the skin through exposure to UVB rays from the sun.
Athletes can obtain vitamin D through diet, sun exposure, and, if necessary, supplements, especially during the winter months or in cases of documented deficiencies.
Intake Limits and Risks of Deficiency
The recommended daily intake varies based on age and health, but for active adults it ranges between 600-800 IU per day, with a safe upper limit set around 4,000 IU per day to avoid toxicity.
A vitamin D deficiency can lead to:
- Muscle weakness and reduced athletic performance
- Osteoporosis and increased risk of fractures
- Increased susceptibility to injury and delayed muscle recovery
- Immune disorders and increased vulnerability to infections
On the other hand, excess vitamin D (from excessive supplementation) can cause hypercalcemia, with negative effects such as kidney stones, nausea, weakness, and heart problems.
(In summary, vitamin D is crucial for athletes, but it must be taken in a balanced way, preferably under medical supervision, to avoid both deficiencies and overdoses.)
The Álvaro Miguel-Ortega study, published in 2025 in Physiological Reports, involved 23 professional athletes, 12 basketball players and 11 volleyball players, all competing in top-level leagues such as the Liga Iberdrola volleyball league and the Liga DIA basketball league. The participants had a mean age of 25.1 ± 4.7 years, a mean height of 1.8 ± 0.1 m, and a mean body mass of 73.9 ± 15.4 kg.
The research took place over the course of a 16-week competitive season, with two assessment periods: at the beginning of the season (T1 – September) and at the end (T2 – January). During both periods, the athletes’ blood vitamin D [25(OH)D] levels were measured and physical performance tests were performed, including:
- Vertical jumps: standing jump (SJ) and countermovement jump (CMJ).
- 20-meter sprint: without changes of direction.
- Intermittent endurance test: to evaluate the VO₂max of female athletes.
Main results
- Vitamin D Levels: Mean vitamin D levels decreased significantly from T1 to T2, from 33.7 ± 14.7 ng/mL to 26.1 ± 7.3 ng/mL, a 22.4% reduction (p < 0.05).
- Physical Performance: Despite the decrease in vitamin D levels, the athletes showed significant improvements in all performance tests:
- Standing Jump (SJ): 4.57% increase.
- Countermovement Jump (CMJ): 6.94% increase.
- VO2max: 4.99% increase (p < 0.05).
- 20m Sprint: 1.83% reduction in time.
Discussion:
The study results indicate a significant decrease in vitamin D levels during the competitive season, despite improvements in the athletes’ physical performance. This discrepancy could be attributed to several factors:
- Reduced Sun Exposure: Indoor athletes, such as basketball and volleyball players, have less exposure to sunlight, the main source of vitamin D synthesis, especially during the winter months.
- Increased Training Load: An increase in training intensity and frequency could negatively affect vitamin D levels, perhaps due to increased metabolic demand or alterations in vitamin D metabolism.
It is important to note that, despite the decrease in vitamin D levels, the athletes showed improvements in physical performance. This suggests that other factors, such as physiological adaptations to training, may compensate for short-term vitamin D depletion. However, chronically low vitamin D levels could have negative long-term health and performance implications.
Practical Implications:
For coaches, physical trainers, and sports nutritionists, these findings underscore the importance of monitoring and managing vitamin D levels in indoor female athletes. Practical strategies could include:
Vitamin D Supplementation: Consider supplementing female athletes’ diets with vitamin D, especially during the winter months or periods of intense training.
- Sunlight Exposure: Encourage outdoor activities when possible to increase exposure to sunlight and promote the natural synthesis of vitamin D.
- Regular Monitoring: Regularly check your vitamin D blood levels to ensure prompt treatment for deficiencies.
Conclusion:
The study by Miguel-Ortega and colleagues highlights a complex relationship between vitamin D levels and physical performance in elite female basketball and volleyball athletes during a competitive season. Despite a significant reduction in vitamin D levels, the athletes improved their performance, suggesting that other training-related factors play a crucial role. However, it is crucial to properly monitor and manage vitamin D levels to ensure the long-term health and optimal performance of athletes.
CITATION:
Miguel-Ortega, A., Calleja-Gonzalez, J., & Mielgo-Ayuso, J. (2025).
Vitamin D and its relationship to performance and health during a competitive period in elite women’s basketball and volleyball players. Physiological Reports, 13, e70224. https://doi.org/10.14814/phy2.70224
REFERENCE – ORIGINAL ARTICLE
