Vitamin D in Athletes: Benefits Beyond Performance

Vitamin D in athletes: benefits beyond performance and the challenge of solar balance

When evaluating the quality of our diet, we often focus solely on the number of calories we consume and the proportion of macronutrients, that is, our intake of proteins, carbohydrates, and fats. However, we must not forget the important role played by other elements such as micronutrients, specifically vitamins, which are essential for the proper functioning of our body. But let's take a closer look at what vitamin D is and what it is used for.

Vitamin D, how do we get it?

Vitamin D can be endogenously synthesized through the contact of the sun's ultraviolet-B (UVB) rays with the skin. In addition, it can also be obtained through the diet, being present for example in foods such as salmon or sardines, milk and fortified cereals, or egg yolk, and its absorption increases with foods high in fat (as it is a fat-soluble vitamin). However, on many occasions it seems that the diet is not enough to reach the recommended levels of vitamin D, and the low sun exposure that most of the population undergoes (especially during the winter months) further prevents us from meeting these recommendations. In fact, as confirmed by a systematic review that included studies conducted in countries around the world, the majority of the population has vitamin D deficiency.(2) In addition, athletes also seem to have generally low vitamin D levels, especially those who practice 'indoor' sports, and this deficiency is more prevalent in countries located at lower latitudes and in athletes with darker skin.(3) Furthermore, although in summer most athletes may have optimal vitamin D levels, in winter it is common for a high proportion (20% approximately) to have a deficiency of this vitamin (4).

Therefore, low sun exposure is one of the factors associated with the high vitamin D deficiency normally observed in athletes. However, a low intake of vitamin D in the diet also seems to contribute to these worrying data, as a study conducted on more than 500 high-level Dutch athletes showed that less than 15% met the recommended vitamin D intake.(5) In view of these results, vitamin D supplementation emerges as a potentially effective strategy, and in fact it has been shown to reduce the number of athletes consuming insufficient levels of vitamin D to less than 30% (while without supplementation this figure reaches more than 85%).(5)

Importance of vitamin D for sports performance

Vitamin D has important repercussions on different systems of our body, including the musculoskeletal system and immune function. Therefore, it is not surprising that numerous studies have observed that a deficiency of this micronutrient can negatively affect performance. For example, a study on nearly 1000 UK military personnel observed that during the winter only 9% of men and 36% of women had sufficient blood levels of vitamin D (6). In addition, lower vitamin D levels were associated with poorer performance in a 1.5-mile running test, although without differences in power or muscle strength, which confirms the relevance of this micronutrient (6). Similarly, another study in young swimmers observed that 45% had vitamin D deficiency, and interestingly those with lower vitamin D levels had lower levels of muscle strength (7) (Figure 1).

Figure 1. Muscle strength in athletes with and without vitamin D deficiency. Obtained from Geiker et al. (7).

It is important to mention that, although blood vitamin D levels are associated with sports performance, there is controversy regarding whether exogenous vitamin D supplementation is always beneficial for performance. Some encouraging results have been published, such as the study led by Dr. Graeme L. Close, which showed that vitamin D supplementation improved sprinting and jumping ability in athletes. (8) On the contrary, in the same year the same authors showed that vitamin D supplementation did not improve any performance variable (including sprints, jumping, and strength). (9) Very recently, a systematic review that included 14 studies confirmed this controversy, although it suggested that vitamin D could provide benefits indifferent disciplines (10). Therefore, it is very possible that vitamin D does not improve performance in all athletes, and that the benefits are mainly applicable to those with a deficiency of this micronutrient. For example, a recent study showed that supplementation with vitamin D along with sun exposure could indeed be beneficial for sprint performance in cases of deficiency of this vitamin (for example, during winter). (11)

Benefits of vitamin D: beyond performance.

On the other hand, vitamin D could be beneficial for factors other than performance. For example, a study published in the prestigious journal American Journal of Sports Medicine showed that athletes with lower levels of vitamin D were more likely to have an injury during the season (which may be partly due to better musculoskeletal system function) (12). Similarly, other studies in large populations of athletes and/or military personnel have shown that low vitamin D levels are associated with a higher incidence of bone injuries (e.g., fractures) (13,14).In addition, another study conducted on 41 athletes followed for a year showed that those with lower levels of vitamin D had a higher risk of contracting diseases (15).

Therefore, beyond performance, vitamin D levels play an important role in athletes' health. In this regard, as confirmed by a recent meta-analysis published in the British Medical Journal, supplementation with vitamin D could decrease – at least in people with a deficiency of it – respiratory infections, (16) which are quite prevalent in athletes. Similarly, another preliminary study in more than 100 athletes showed that supplementation with vitamin D reduced the incidence of injuries from 7.5% in previous years to 1.7% after beginning supplementation (17).

Conclusions

In summary, vitamin D plays an important role in various functions for health and sports performance. However, a large part of the population – including athletes – has a deficiency of it, especially when there is low sun exposure. Supplementation arises as an effective strategy to improve blood levels of this vitamin and prevent its deficiency, and although more studies are still needed to confirm the direct effects of supplementation on physical performance, it does seem to provide benefits in other variables such as the risk of injury or disease. Vitamin D supplementation can therefore be recommended as it is safe and can provide benefits, at least in people with a deficiency of it.

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Author

Pedro Valenzuela
Researcher in the Physiology Unit of the University of Alcalá and in the Performance Control Unit at the Sports Medicine Center (AEPSAD, CAR of Madrid).
Web: www.fissac.com

References

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