Understanding positive and negative effects of solar UV-radiation: A challenge and a fascinating perspective

There is an ongoing debate how to balance between beneficial and adverse effects of UV-exposure. On the one hand, solar UV-radiation represents the most important environmental risk factor for the development of non-melanoma skin cancer. Therefore, sun protection is a key principle to prevent these malignancies, especially in risk groups. On the other hand, artificial or solar UV-radiation is required for the cutaneous synthesis of vitamin D, that covers approximately 90% of the vitamin D-requirements of the human body. Therefore, lack of UV-exposure is associated with an increased risk to develop vitamin D-deficiency. We know today that vitamin D-deficiency represents a serious health problem, for an association of vitamin D-deficiency and multiple independent diseases including various types of cancer, bone diseases, autoimmune diseases, infectious diseases, hypertension and cardiovascular disease has now been clearly indicated in a large number of laboratory and epidemiologic studies. As a consequence, it has been assumed that the net effects of solar UV B-radiation on human health are beneficial at or near current levels. We and others have shown that strict sun protection causes vitamin Ddeficiency/insufficiency and that detection and treatment of vitamin Ddeficiency in sun deprived risk groups is of high importance. Although further work is necessary to define an adequate vitamin D-status and adequate guidelines for solar and artificial UV-exposure, it is at present essential that public health campaigns and sun protection recommendations to prevent skin cancer consider these facts. In this review, we analyze the present literature on the way to develop well-balanced recommendations on sun protection that ensure an adequate vitamin D-status. These recommendations will hopefully