Vitamin D during the dark season

Paolo Colombani 15. November 2017

The research interest in vitamins is now clearly fixated on vitamin D. Over the last 15 years, the number of scientific studies on the sunshine vitamin has increased from almost 1000 to 4000 per year. What precisely makes vitamin D so interesting and should you pay particular heed to it when doing sports?

Vitamin D occupies a special position among vitamins. Strictly speaking, it is not actually a vitamin, but a hormone-like substance. And it is also not one single substance, but a combination of ergocalciferol (vitamin D2) and cholecalciferol (vitamin D3). However, the main reason why vitamin D occupies an exceptional position among vitamins is this: people are able to build up a sufficient quantity of vitamin D in the skin itself, which is not the case with all the other vitamins.

It can’t be made without sun

To be able to produce vitamin D at all, our skin needs sufficient exposure to intense sunlight. If we spend too little time in the sun or are always covered up, or if the intensity of the sun is weak, then the body cannot produce vitamin D. It is only thanks to the sun that we are actually able to make enough vitamin D. The fear of getting skin cancer, however, is causing us to avoid the sun more and more frequently or constantly cover ourselves in sunscreen. Yet it has long been known that even a factor 8 sun cream will prevent the production of vitamin D.

It is difficult to get enough vitamin D without the sun because the vitamin D content in food is very low. Unless you eat 300 g of oily salmon each day, you won’t manage it without sun. The alternative would then be supplements.

Tank up in the summer for winter

The skin no longer makes vitamin D in the winter due to the weaker sunlight – even if we go out in the sun. This applies to Switzerland and Europe. We should therefore frequently soak up the sun in the summer and build up a reserve of vitamin D, so to speak. The vitamin D that is stored in your fat will then help you through the winter months when the sunshine is weak. This means it is important to go out in the sun without any sun cream while making sure that you don’t get burnt. As with everything else, moderation is key. It is neither ideal to stay in the sun for too long and get sunburnt nor completely avoid the sun or always wear sun cream.


How much sun is enough?

The production of vitamin D mainly depends on the skin type, the location, and time of year. The Swiss Federal Office of Public Health has estimated that staying in the sun for 5 minutes in the summer in Switzerland will sufficiently meet your daily requirements if the sun shines on your face, arms, and hands.
Vitamin D and bones

Vitamin D was formerly known as the vitamin for bones because a prolonged and severe vitamin D deficiency results in deformed bones. A lot of research in recent years, however, has led to the discovery of new vitamin D effects. Sufficient vitamin D contributes to normal muscle function as well as the functioning of the immune system and is therefore a hotly debated topic in sports. 
Vitamin D in sports

In sports today, chronic fatigue is not only thought to be due to an iron deficiency, but also to a lack of vitamin D. And it’s true. When there is a vitamin D deficiency, both the metabolic processes and performance in sports become less than optimal. Corresponding improvements are seen if the too-low level of vitamin D in the blood is normalised. The administration of additional vitamin D when there is already enough vitamin D in the body, however, will not bring about any further improvements. And as is the case with all nutrients, you can also take too much vitamin D. Blood levels of 125 nmol/L and higher should be avoided because adverse health effects can then no longer be ruled out. It is therefore not advisable to take a vitamin D supplement blindly without consulting your doctor.

Low vitamin D levels are just as likely to occur in athletes as in the population at large. According to estimates by the Federal Office of Public Health, around 50% of the people in Switzerland have a level lower than 75 nmol/L. And findings from a representative current study on Swiss sports show that the situation in sports is practically the same: 50% of the athletes have a vitamin D level of less than 75 nmol/L in their blood.

Summed up for use in practice

  • Vitamin D is made in the skin with the help of the sun; the diet only provides a small amount of vitamin D.
  • Controlled exposure to the sun in summer is therefore good for you; the sun in winter is too weak to produce enough vitamin D.
  • Less than 75 nmol/L of vitamin D in the blood is considered insufficient; around half of the Swiss population including athletes have less than this target value.
  • A blood analysis towards the end of Autumn will show whether you made enough vitamin D over the summer to see you through the dark season.
  • You should consult your doctor about taking vitamin D supplements to correct a deficiency.