[The significance of vitamin D metabolism in human skin. An update].

Vitamin D deficiency is endemic, affecting worldwide approximately more than 1 billion people and approximately 60% of the German population. In recent years, our understanding of the important role of vitamin D for human health has grown enormously. Epidemiological and in vitro investigations as well as animal studies have convincingly demonstrated new important functions of vitamin D, including potent immunoregulatory and growth regulatory properties. We know today that vitamin D deficiency/insufficiency is not exclusively associated with an increased risk for bone diseases, but with a multitude of other diseases (including various types of cancer, cardiovascular diseases, infectious diseases, and autoimmune diseases). We discuss our present understanding of the importance of the cutaneous vitamin D system.