Types and sources
The substance we usually refer to as vitamin D is 1,25–dihydroxyvitamin D3 (calcitriol), an active molecule that is metabolised inside our body.
There are two main types of vitamin D:
1. Colecalciferol (vitamin D3), of animal origin, found in fish oils and to a lesser extent in beef liver, egg yolks and cheese.
2. Ergocalciferol (vitamin D2), which is of plant origin and is mainly produced by fungi and yeasts.
Both types are converted to the active molecule calcitriol inside the human organism.
As to its sources, there are two ways to obtain vitamin D: through ingestion (diet, supplementation) or sun exposure. The latter is the so-called endogenous production of vitamin D: 7-Dehydrocholesterol, a cholesterol precursor, is converted to colecalciferol in the skin on contact with ultraviolet rays.
Main functions of vitamin D
Vitamin D has a regulatory function in calcium and phosphate homeostasis and thereby crucial for bone health. It also plays an essential role in the modulation of the immune response by binding to a specific receptor (the vitamin D receptor, VDR) found in various tissues and in immune cells such as dendritic cells, macrophages, CD8+ and CD4+ T lymphocytes and B lymphocytes.
· Regarding innate immunity, calcitriol can promote the antimicrobial activity of monocytes and macrophages, increasing phagocytosis, chemotaxis and the production of antimicrobial peptides. Vitamin D is thus key in the prevention of infections
Preventing vitamin D deficiency
Since sunlight constitutes the main source of vitamin D, the production of this substance is insufficient during winter, whereby colds and flus are much more frequent. Moreover, vitamin D deficiency is also associated with depression, explaining the higher rate of seasonal psycho-emotional disorders in northern regions with less sunlight.
Given that vitamin D is crucial for bone health, immune function and psycho-emotional balance, it is recommended to check the vitamin D level via a 25-Hydroxy Vitamin D Test. In case of deficiency, supplementation can help reach an adequate level, strengthen immunity and optimise the effect of micro-immunotherapy.
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