Vitamin D deficiency is linked to multiple poorer health outcomes, including survival rates with COVID-19, heart disease risk, diabetes, autoimmune diseases, and even some cancers.
Vitamin D and Athletic Performance
Research on vitamin D and athletes is particularly fascinating. Our bodies have receptors for vitamin D on most cells, including muscles. Vitamin D deficiency in athletes has been associated with decreased muscular power, increased injuries (especially of the lower limbs), longer recovery times after injury, and increased illnesses. While it’s challenging to prove causation versus association, athletes are an interesting group to study since typical confounding factors like frailty and being housebound don’t apply.
Focus on Respiratory Illnesses in Winter
This post focuses on respiratory illnesses during winter, which is particularly relevant now.
A study of 225 endurance athletes (average training 10 hours/week) categorized vitamin D status as follows:
- Deficient: < 30
- Inadequate: 30-50
- Adequate: 50-120
- Optimal: >120
Over four months, 27% of athletes with optimal vitamin D levels had an upper respiratory tract infection (URTI) compared to 67% of those who were deficient. The symptom score for deficient athletes was higher (102 vs. 43), and the length of illness was significantly longer (13 vs. 5 days). Preventing illness helps maintain consistent training, thereby improving performance. While >120 is quite high for optimal levels and leaves a narrow window for potential toxicity, even adequate vitamin D levels show benefits compared to being deficient or inadequate.
Benefits of Vitamin D Supplementation
Although this post doesn’t specifically review the benefits of vitamin D supplementation, smaller studies, such as one involving Taekwondo athletes over four weeks, showed that vitamin D supplementation decreased rates of respiratory illnesses. A larger meta-analysis found that daily or weekly vitamin D supplementation decreases URTIs by 12%.
Conclusion
In summary, maintaining sufficient vitamin D levels is highly likely to decrease the risk of colds during winter, including for endurance athletes. It may also benefit performance, recovery, and injury prevention. Unless you’re living in a tropical paradise, most people, even athletes who train outside, will need supplementation during winter. ☀️