Vitamin D in trichology: a comprehensive review of the role of vitamin D and its receptor in hair and scalp disorders.

Vitamin D plays an important role in maintaining the homeostasis of various biological systems. Beside its well-known function in calcium and phosphate metabolism, it plays a major role in pathophysiology of skin and adnexa. Indeed, vitamin D, through its receptor (VDR), decreases keratinocyte proliferation, improves their differentiation and modulates both cutaneous innate (antimicrobial activity and antigen presentation) and adaptative immunity (T and B lymphocyte function). The maintenance of normal hair is dependant on the integrity of the dermis, epidermis and hair cycles. Beside its effect on epidermal differentiation, VDR plays a vital role in preserving the hair follicle integrity. While the relevance of VDR has been fully elucidated, the real value of vitamin D in the hair follicle cycle still remains uncertain. To date, results in literature remain contradicting and far from definitive; still, the role of vitamin D in the various forms of human alopecia is likely to be significant. The aim of this article is to review evidence about the role of vitamin D and its receptor in trichology, with a focus on scarring and non-scarring alopecia and in particular on the potential therapeutic use of Vitamin D for hair and scalp disorders.