Summary

Vitamin D deficiency/insufficiency is an endemic, affecting worldwide approximately more than one billion people and in Germany approximately 60% of the population in all age groups. During the last decades, our understanding of the important role of vitaminD for human health has increased enormously. Epidemiological studies, in vitro investigations and animal studies have convincingly shown new important properties of vitamin D, including potent effects on the immune system and cellular growth. It is nowadays accepted in the scientific community that vitamin D deficiency/insufficiency is not only associated with an increased risk for bone diseases, but with a multitude of other important diseases (including various types of cancer, cardiovascular diseases, infectious diseases, and autoimmune diseases). In this article, we discuss our present understanding of the relevance of the cutaneous vitamin D system for human health.