COVID-19 and vitamin D. Position paper of the Spanish Society for Bone Research and Mineral Metabolism (SEIOMM)

Vitamin D exerts its effect mainly through its active metabolite, 1,25-dihydroxycholecalciferol, by binding to a receptor with wide distribution in the different cells of the body. This receptor regulates the expression of genes involved in different biological functions, including organ development, cell cycle control, phosphocalcic metabolism, detoxification, and control of innate and adaptive immunity [1,2]. Regulation of the vitamin D receptor is determined by interacting environmental, genetic, and epigenetic factors.
Vitamin D increases intestinal absorption and tubular reabsorption of calcium, inhibiting PTH synthesis. This leads to a reduction in bone turnover, which helps maintain its strength and reduce the risk of fractures. In addition, it exerts an intraosseous effect, facilitating the mineralization of the matrix, which prevents the development of rickets in children and osteomalacia in adults. Numerous studies have been published showing an association between low levels of vitamin D and various chronic diseases, such as cancer, diabetes, cardiovascular diseases, multiple sclerosis, and infectious diseases, among others [3]. These associations can be explained through different pathophysiological mechanisms related to vitamin D deficiency.

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