
Vitamin D
The sun vitamin. Vitamin D deficiency can occur in all people. Vitamin D is produced by the body itself as long as the skin is exposed to the sun. From October to March, the sun’s rays are too weak for the body to be able to produce vitamin D. In this blog, you will learn the most important facts about vitamin D and what you can do to prevent a deficiency.
Functions
Vitamin D maintains a healthy balance of calcium and phosphate in the blood (homeostasis), plays a role in gene modification and signal transduction, has numerous protective functions with regard to chronic diseases and a wide range of regulatory effects. Vitamin D plays a significant role in the immune system, influences insulin secretion, affects the growth of skin cells and inhibits the growth of tumour cells.
Deficiency
A vitamin D deficiency can increase the risk of bone fractures or even lead to osteoporosis or rickets, as the calcium balance becomes unbalanced. Furthermore, muscle diseases can develop and disorders of the nervous system and blood clotting can occur. Since the immune system is weakened in the case of a vitamin D deficiency, this leads to an increased susceptibility to infections. An insufficient vitamin D supply correlates with the occurrence of certain diseases.
Occurrence
Although animal products, such as fish, liver and milk, contain vitamin D, diet does not play a major role, since only 10-20 % of the requirement can be absorbed through food. On the other hand, up to 90 % of the requirement can be covered by supplements or synthesis. The human skin produces vitamin D itself (synthesis) when exposed to the sun. To do this, about 25 % of the skin should be exposed to the sun for about 5 – 30 minutes several days a week from March to October without sunscreen. In Europe, sunlight is too weak for synthesis in the winter half-year. Even in summer, it is only strong enough at midday in northern regions. When it comes to the duration of sunbathing, it is important to consider your own skin type. Not only are lighter skin types more at risk of burning themselves, they also produce more vitamin D. Therefore, fair skin types do not need to take a long sunbath. On the other hand, heavily pigmented skin types in European latitudes are more likely to be affected by vitamin D deficiency. Just like older people and people who are overweight, they can synthesize vitamin D less well. In such cases, supplementation should be considered throughout the year.
Supplementation
Opinions differ when it comes to supplementation recommendations. The rather conservative recommendation of the DGE recommends a daily supplementation of 800 IU (international units) for children (1-15), adolescents and adults (15-65), the elderly (65+), pregnant and breastfeeding women, provided there is no exposure to the sun (rainy days, winter half-year, etc.). More recent sources and voices from complementary medicine recommend a daily intake of 2000 to 4000 IU as a maintenance dose for adults. The body weight is taken into account. A simple formula is, for example, 40 IU * body weight (in kg) as a daily dose. Vitamin D is fat-soluble. For better absorption, it is recommended to eat a meal with little fat (2 – 3 walnuts are sufficient). Attention! Since excess vitamin D is not excreted, side effects may occur if the dosage is too high. As mentioned above, in European latitudes, supplementation is necessary for the entire population during the winter months. Unfortunately, there is no public discourse on this and so many people suffer from vitamin D deficiency in winter.
Diagnostics
The analysis takes place by means of 25-cholecalciferol in the serum. A value of 50nmol/l or more is sufficient. If the value is below 30nmol/l, there is a pronounced vitamin D deficiency.


