Vitamin D plays a crucial role in regulating immune system activity – both innate and adaptive responses. The innate immune system is responsible for the initial defensive front with a central role played by phagocytes. Vitamin D stimulates expansion of these phagocytes (monocytes and macrophages), increasing their ability to fight off the virus by increasing their numbers, as well as increasing their killing capacity through stimulating the production of the anti-viral and anti-microbial protein cathelicidin. Vitamin D also acts to regulate the maturation of dendritic cells which are important for activating CD4+ T cells and in turn the rest of the immune response (see more below).
Vitamin D is a potent regulator of both cell-mediated (T cell) and humoral (B cell) immunity. This is a vital part of the body’s defence against pathogenic invader, allowing white blood cells to recognise, bind to and destroy pathogens – a process that relies on vitamin D to function properly.
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