Résumé
Vitamin D is a steroid hormone that plays a crucial role in maintaining normal bone condition and calcium homeostasis. In recent years, vitamin D has become a hot topic of endocrino-logical research, largely Due to the COVID-19 pandemic and the likely correlation between hypovitaminosis D and a high risk of chronic lung disease and associated mortality. Recent studies have shown that vitamin D exhibits a complex multistage metabolism and acts as a hormone on many extracellular targets. This review examines some new intriguing and as yet unclear aspects of vitamin D metabolism, such as new concepts of enzyme regulation, new pleiotropic effects of vitamin D receptor activation (VDR), and epigenetic effects. The mechanisms of vitamin D synthesis in the skin, its metabolism in the hepatic cytochrome P450 system, catabolism, metabolites and transport, gene control and epigenetic modulation are considered in Detail. In addition to the well-known role of vitamin D in calcium and bone metabolism, it has many pleiotropic extraskeletal effects, including potent effects on the immune system, cardiovascular system, adipose tissue and glucose/ lipid metabolism, muscle and more. Experimental studies have shown that VDRs are expressed by cancer cell lines. Recent studies have shown a link between low levels of vitamin D and almost all aspects of the metabolic syndrome, such as type 2 diabetes, fasting blood glucose, hypertension, dyslipidemia, obesity and insulin re-sistance. Several studies have focused on the role of vitamin D in adipose tissue biology. In particular, a negative correlation between vitamin D and leptin or resistin is shown, as well as an inverse correlation with adiponectin. Recent studies in vitamin D-deficient mice have shown impaired secretion of glucose-stimulated insulin by pancreatic islets. Vitamin D is thought to play a role in the pathogenesis and progression of cancer, and vitamin D analogues can slow cancer progression and metastasis. It is concluded that vitamin D is a molecule with several endocrine, paracrine and auto-crine effects on many tissues and organs, in addition to maintaining skeletal homeostasis. Research in this area, which aims to clarify the pleiotropy of many effects of vitamin D and its metabolites, continues. © 2022, Zaslavsky Publishing House. All rights reserved.