Vitamin D and Sports Performance
by Clare Wood
Vitamin D is a pro-hormone that plays a vital role in maintaining calcium and phosphate balance in the body, optimizing bone mineralization and the functioning of our skeletal muscle. It is mainly produced in the skin from direct UVB sunlight rays, with a very small amount coming from naturally occurring and fortified food sources.
Vitamin D deficiency
The best indicator of vitamin D status is the concentration of 25-hydroxyvitamin D 25(OH)D in the blood.
There is also growing evidence to suggest that many athletes are Vitamin D insufficient, up to rates of 40%, as well as deficient athletes, with the worst case seen in in middle-eastern athletes. Generally there are seasonal differences with lower Vitamin D levels seen in winter, as well as in indoor trained athletes. This may be important for the training and performance of athletes.
Athletes appear to have the same risk of vitamin D deficiency as non-athletes. Athletes who are at greater risk of deficiency include whose who:
- Train indoors
- Train only in the early morning and late afternoons,
- Always cover up their skin,
- Regularly apply sunscreen,
- Live in a cool cloudy environment.
Effect on Performance
It is likely that poor vitamin D status can affect an athlete’s health and ability to train. One meta-analysis suggests that Vitamin D may improve physical performance, but results have been seen mostly in older individuals. There have also been some improvements in muscle performance and bone mineral density in vitamin D supplemented athletes, but mostly in participants with initial low status. Again researchers have not been able to show sporting improvements through vitamin D supplementation.
With the high prevalence of vitamin D deficiency and insufficiency in the general population as well as athletes, plus the potential health benefits of supplementation, improving vitamin D status seems warranted. The improvement of Vitamin D levels can be made using the following strategies:
- Sun Exposure: some sun exposure is essential to maintain acceptable Vitamin D levels. Current sun exposure guidelines are cautious to avoid skin cancer, and provide challenges due to the variability of individual skin types, distance from equator, and time of the year. Although there is minimal risk of vitamin D toxicity through sun exposure, it is not the safest way to improve vitamin D status.
- Dietary sources: There are only a few dietary sources of vitamin D from limited natural and fortified foods including fatty fish, egg yolks, sun-dried mushrooms, and fortified milk, margarine, and cereals. Dietary recommendations for vitamin D intake are generally not well achieved by athletes, therefore dietary advice from a sports dietitian to optimize intake is important.
- Supplementation: studies have shown that individual supplementation in athletes can achieve vitamin D sufficiency and is recommended in the winter months to maintain levels for those at risk.
- Food Fortification: vitamin D food fortification is in different stages around the world.
There is enough evidence to suggest that deficiency and insufficiency are widespread in the general population, which includes a high prevalence in athletes. However, there is currently insufficient evidence to show that vitamin D supplementation can improve exercise performance. Therefore routine supplementation is not justified for all athletes, unless they are specifically at risk. Athletes presenting with stress fractures, musculoskeletal pain, frequent illness, plus idiopathic muscle weakness (heaviness in the legs), overtraining injury, or respiratory tract infections plus other risk factors such as low sun exposure during training, should be targeted for assessment by a qualified Physician or Sports Dietitian.
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- Vitamin D – the effect of deficiency on health
- Vitamin D Testing
- Vitamin Supplements
- Guide to Athletic Supplements