When sunlight shines in, the human body forms vitamin D in the skin itself. From March to October, the sunshine in our latitudes is sufficiently strong to enable a good supply through the body’s own vitamin D formation. This does not even require excessive sunbathing: regular short stays (15 to 25 minutes) or walks in the fresh air are sufficient. “Specifically, it is recommended to expose the face, hands and arms two to three times a week and only for a short time without sunscreen,” says Silke Raffeiner, nutrition expert at the South Tyrolean consumer center. The skin can also produce vitamin D in the morning and late afternoon, even in the shade. The skin should always be protected with a sunscreen, especially at lunchtime.
In the cold season, the sun is too weak to provide the body with sufficient amounts of vitamin D formed in the skin. However, since the vitamin is fat-soluble and can be stored in the liver, body fat and muscles, it is possible to “provide” in the spring and summer by spending time outdoors and to survive in winter with the excess stored in the body.
The body’s own vitamin D formation is so important because only a small part of the need can be met through food, only around ten to 20 percent. Because only a few foods contain vitamin D: these are mainly fatty sea fish such as salmon and herring, egg yolk, liver and wild mushrooms.
Nutritional societies only recommend taking vitamin D supplements (drops or similar) if there is insufficient supply and regular outdoor stays are not possible. This applies to some older people, to sick or people in need of care, also to people with chronic diseases of the intestine or kidneys and to women who disguise themselves for religious reasons. The use of a vitamin D supplement is recommended for infants throughout the first year of life. Overdose should be avoided when taking a preparation, as this can cause kidney stones or calcification of the kidneys.