Vitamin D plays important, pleiotropic role in the maintenance of global homeostasis. Its influence goes far beyond the regulation of calcium and phosphorus balance, as diverse activities of vitamin D and its natural metabolites assure proper functioning of major human organs, including skin. Recently, we reviewed the current understanding of vitamin D impact on human health from historical perspective (Wierzbicka et al. (2014) The renaissance of vitamin D. Acta Biochim Pol 61: 679-686). This article focuses on its functions in the skin. The skin and its appendages, creates a platform connecting and protecting internal organs against, usually harmful, external environment. It uppermost layer - epidermis in order to maintain a protective barrier undergoes a constant exchange of cornified keratinocytes layer. Its disturbance leads to development of serious skin disorders including psoriasis, vitiligo, atopic dermatitis and skin cancer. All of those dermatopathologies have a huge impact on modern societies, affecting not only the physical, but also mental state of patients as well as their social status. Furthermore, multiple human systemic diseases (autoimmune, blood and digestive diseases) have skin manifestation, thus "condition of the skin" often reflects the condition and pathological changes within the internal organs. In humans, the skin is the natural source of vitamin D, which is produced locally from 7-dehydrocholesterol in photoreaction induced by ultraviolet B (UVB) radiation from the sun. It is also well established, that the process of proliferation and differentiation of keratinocytes is tightly regulated by calcium and the active form of vitamin D (1,25(OH)2D3). Thus, the skin physiology is inseparably connected with vitamin D production and activity. Unfortunately, UVB, which is required for vitamin D production, is also known as the main cause of a skin cancer, including melanoma. Here, we are going to review benefits of vitamin D and its analogues in the maintenance of epidermal barrier and its potential use in the treatment of common skin diseases.
There is no doubt that vitamin D plays a crucial role in the maintenance of musculoskeletal system. But the function of this ancient molecule presumably ranges far beyond hormone-like regulation, as it could be generated by simple unicellular organisms. First, we are going to discuss the role of vitamin D as a global regulator of homeostasis from a historical perspective, but later we will focus on current views and its relevance to human physiology and pathology. Three milestones are defining the impact of vitamin D on science and humanity. Firstly, discovery that vitamin D is the cure for rickets, brought us supplementation programs and rapid irradiation of this devastating disease. Secondly, detail description of photoproduction of vitamin D, its subsequent metabolism and interaction with vitamin D receptor VDR, provided mechanistic background for future discoveries. Finally, recent large epidemiological studies provided indirect, but strong evidence that optimal level of vitamin D in serum has beneficial effects on our health and protects us from multiple diseases, including cancer. Furthermore, existence of alternative pathways of vitamin D metabolism and multiple intracellular targets broadens our understanding of its physiological activities and offers new and very promising tools for prophylactics and treatment of many diseases of civilization. Although vitamin D (and its derivatives) should not be regarded as a cure-all for every human disease, its beneficial effects on the human health have to be taken under consideration.
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