Challenge and perspective: the relevance of ultraviolet (UV) radiation and the vitamin D endocrine system (VDES) for psoriasis and other inflammatory skin diseases

Abstract

During evolution, the ability of many organisms to synthesize vitamin D photochemically represented, and still represents, a major driving factor for the development of life on earth. In humans because not more than 10-20% of the requirement of vitamin D can be satisfied by the diet (under most living conditions in the US and Europe), the remaining 80-90% need to be photochemically synthesized in the skin through the action of solar or artificial ultraviolet-B (UV-B) radiation. The skin is a key organ of the human body's vitamin D endocrine system (VDES), representing both the site of vitamin D synthesis and a target tissue for biologically active vitamin D metabolites. Human keratinocytes contain the enzymatic machinery (CYP27B1) for the synthesis of the biologically most active natural vitamin D metabolite 1,25-dihydroxyvitamin D (1,25(OH)D), representing an autonomous vitamin D pathway. Cutaneous production of 1,25(OH)D may mediate intracrine, autocrine and paracrine effects on keratinocytes and on neighboring cells. Many skin cells (including keratinocytes, sebocytes, fibroblasts, melanocytes, macrophages and other skin immune cells) express the vitamin D receptor (VDR), an absolute pre-requisite for exerting genomic effects of 1,25(OH)D and analogs. The VDR is a member of the superfamily of trans-acting transcriptional regulatory factors, which also contains the steroid and thyroid hormone receptors as well as the retinoid-X receptors (RXR) and retinoic acid receptors (RAR). A large body of evidence, including cDNA microarray analyses of mRNAs, indicates that as many as 500-1000 genes may be controlled by VDR ligands that regulate a broad variety of cellular functions including growth, differentiation, and apoptosis. Clinical and laboratory investigations, including the observation that 1,25(OH)D is very effective in inducing the terminal differentiation and in inhibiting the proliferation of cultured human keratinocytes have resulted in the use of 1,25(OH)D and analogs for the treatment of psoriasis. Focussing on the UV-induced cutaneous synthesis of vitamin D, this review gives an update on the relevance of the VDES and of UV radiation for the management of psoriasis and other inflammatory skin diseases.

Association of serum 25-Hydroxyvitamin D with Vitamin D intervention and outdoor activity among children in North China: an observational study

“…However, duration and sun-exposed skin areas of each child was not investigated in this study. Third, < 10-20% vitamin D that human needed per day was from diet [42], which played an important role in the vitamin D status of children. However, such information was unavailable in our study.…”

Vitamin D status and dental caries in healthy Swedish children

“…Vitamin D is associated with a broad spectrum of biological functions owing to its endocrine, autocrine and paracrine activities [ 1 ]. Its reported functions include the regulation of calcium and phosphate metabolism and their deposition in mineralized tissues [ 2 , 3 ], effects on innate immunity effectors [ 4 ], involvement in cognitive functions, roles in blood pressure maintenance and effects related to health outcomes (cardiometabolic conditions, total mortality and aging) [ 5 , 6 ].…”

Effect of Vitamin D Intervention and outdoor activity on serum 25-Hydroxyvitamin D among children in North China: an observational study

“…However, duration and sun-exposed skin areas of each child was not investigated in this study. Third, <10%-20% vitamin D that human needed per day was from diet [40] , which played an important role in the vitamin D status of children. However, such information was unavailable in our study.…”