Vitamin D and immune system: between health and sports performance

The common belief lead us to think that it is concentrated only in dairy products. Actually, few people know that because of its source, it is also called “sunshine vitamin”. We are talking about vitamin D., a precious vitamin for the well-being, from childhood to old age. And it is precisely about its benefits, the sources that can offer it in greater quantities, as well as the useful strategies to synthesize it more effectively and its impact on sports performance that I want to tell you in the next few lines.

What is vitamin D used for?

Let’s start from the beginning. Vitamin D is valuable in controlling blood levels of the mineral calcium and phosphates. That’s why it helps to fix calcium in bones and teeth so as to make them stronger. It also supports the maintenance of muscle strength. Finally, it also has a positive impact on the efficiency of the immune system, nerve and cardiovascular functions.

How much is needed?

The daily requirement of vitamin D for an adult is 400 units per day, in the absence of risk factors. This requirement varies according to age. Moreover, in the presence of risk factors or deficiency, quantities can vary and reach up to 1.000 units per day.

Where is it?

Vitamin D is present in the body, mainly in the liver and is essential for the reabsorption of calcium in the intestine and kidneys. It comes in two forms: ergocalciferol, which is taken with food, e cholecalciferol, which is synthesized by our body. There are two main sources: food and sunlight. Through the consumption of food that contain it (oily fish, milk and dairy products, eggs, liver and green vegetables), mostly in an “inactive” form. For it to activate itself and thus offer its benefits, it is essential that it is “activated” by the type B ultraviolet (UVB) sun rays. Already 20-40 minutes per day of sun exposure, especially on the “long” limbs such as arms and legs, are sufficient to reach satisfactory levels. It goes without saying that it is fundamental to use sun creams with protective filter when in the sun, despite them partially reducing the activation of vitamin D.

Sun exposure

Without a doubt, during the summer season, spending some time active or relaxing with adequate sun protection of course, is already a way to get your intake of vitamin D. But is also necessary to know that bones can absorb more vitamin D when subjected to pressure. Walking, running and cycling are therefore an optimal strategy for staying active, toned and strong. A practical solution that can be adopted in any place and at any age, and during summer when lower sunlight and always with an adequate amount of water and minerals to stay properly hydrated.

Vitamin D and immune system:

The probiotic bacteria present in the intestine, mostly belonging to the genera Lactobacillus and Bifidobacterium, offer several health benefits, for example like protecting against vitamin deficiency.
The active form of the vitamin D hormone, 1,25-dihydroxyvitamin D (1,25OHD, also called VDR), regulates gene expression especially in immune function and inflammation and helps maintain tight junctions, gap junctions and adherent junctions. Viral diseases affect the integrity of junctions thereby increasing the incidence of infections in the host. For this reason, a vitamin D deficiency can increase the risk of viral infections.

Studies have demonstrated the importance of vitamin D directly or indirectly in fighting infection caused by virus such as rotavirus and influenza. In Covid-19, the increased effect of mortality in the elderly may be due to the reduction in serum concentrations of 1,25OHD with age. The immunomodulatory effects of vitamin D act on both innate and adaptive immune systems, thereby reducing the risk of infection and mortality. For this reason, it is essential to have optimal values of vitamin D in the body, whose risk of deficiency is in the periods of lower solar radiation that is associated with a higher surface area of skin covered with tissues and thus protected by UVB rays.

Vitamin D and sports performance:

There is also a correlation between vitamin D and sports performance. In fact, there are several studies that highlight the correlation between vitamin D and physical exercise, regardless of the age of the subjects, particularly on muscle trophism and strength. It is already known that vitamin D improves protein synthesis in muscle cells by activating intracellular receptors, promotes physical capacity, muscle strength, mass and endurance, while maintaining the right level of energy and also seems to be able to reduce late muscle pain (Doms) induced by exercise. On the other hand, a deficiency can compromise motor coordination, muscle strength and endurance, as well as increase the risk of muscle damage. Generally, the literature reports the minimum limit of 25OHD3 capable of supporting adequate physical activity to be 50 ng/ml.

If adequate levels of vitamin D are essential for sports wellness and health more generally, there is still not enough evidence on the supplementation of this vitamin and increased performance. This does not mean that this ability has been denied by scientific evidence but that, on the contrary, there are no sufficiently controlled and large enough studies to date. Although a recent publication (1) by the team of Prof. Neil Walsh of Bangor University in Wales has started to show significant data in 2 studies summarized below.

Study 1: vitamina D-related performance

In the first study, all 967 participants completed a 1,5-mile (2.4 km) run, and maximum dynamic lift and explosive power were assessed. All participants underwent preliminary blood tests to check vitamin D levels and it was found that during the winter only 9% of men and 36% of women showed sufficient vitamin D values. When the researchers correlated vitamin D status with performance measurements, they found that there was a correlation between vitamin D levels and endurance performance in both men and women. Vitamin D status justified variations between performance of approximately 5%. Each 1 nmol / L increase in vitamin D resulted in a run over the distance tested (2,4 km or 1,5 miles) 0,42 seconds faster. In contrast, there were no correlations with maximum dynamic lift or explosive power.

Study 2: unaffected performance

In the second study, 137 men underwent simulated sunlight or vitamin D3 supplements or placebo (placebo supplement or a simulated light with placebo). Both treatments (sunlight and supplements) were affective in achieving the minimum amount of vitamin D (in 97% of all participants). However, performance was not affected by supplementation. Authors discuss that perhaps the duration of supplementation (12 weeks) was not long enough to see significant effects.

On one point, however, all the authors agree: constantly check vitamin D values and start a possible supplementation in case of need under medical supervision before the beginning of the winter season to maintain constant levels and avoid major deficiencies. A suggestion that should be adopted by the entire population.