Vitamin D deficiency is very common. Rachitis, osteoporosis, cancer, sclerosis as well as cardiovascular diseases are related to vitamin D deficiency. Elderly people, immigrants as well as patients with malabsorption diseases often have vitamin D deficiency. 90-95 % of the total vitamin D requirements are obtained from the ultraviolet (UV) radiation of the skin.In spite of the risk of skin-cancer, treatment with sunlight radiation is often recommended against vitamin D deficiency. This fact has raised a scientific debate, where concern has been expressed with regard to the risk of skin-cancer. This dilemma should also be examined as no human studies are available on the vitamin D production in the skin after UV-radiation showing the frequency and dose necessary for sufficient production of vitamin D. The lowest exposure frequency, the smallest body surface area and the lowest UV dose should therefore be established to be exposed in order to minimize the risk of skin-cancer by unnecessary UV-radiation. The purpose of the project is therefore to clarify which factors there are of importance for the production of vitamin D in the skin after UVB radiation.