Vitamin D regulation of the immune system and its implications for COVID-19: A mini review

Abstract

The novel coronavirus named severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is at the origin of the current pandemic, predominantly manifests with severe respiratory symptoms and a heightened immune response. One characteristic of SARS-CoV-2 is its capacity to induce cytokine storm leading to acute respiratory distress syndrome. Consequently, agents with the ability to regulate the immune response, such as vitamin D, could become tools either for the prevention or the attenuation of the most severe consequences of the coronavirus disease 2019 (COVID-19). Vitamin D has shown antimicrobial as well as anti-inflammatory properties. While SARS-CoV-2 promotes the release of proinflammatory cytokines, vitamin D attenuates the release of at least some of these same molecules. Inflammatory cytokines have been associated with the clinical phenomena of COVID-19 and in particular with its most dangerous complications. Therefore, the goals of this article are as follows: first, present the numerous roles vitamin D plays in modulating the immune response; second, gather data currently available on COVID-19 clinical presentation and its relation to cytokines and similar molecules; third, expose what it is known about how coronaviruses elicit an inflammatory reaction; and fourth, discuss the potential contribution of vitamin D in reducing the risk and severity of COVID-19.

Keywords: ARDS; SARS-CoV-2; calcidiol; calcitriol; cytokine storm; immune response; inflammation; pandemic.

Figure 1.

Synthesis of metabolically active vitamin D (1,25(OH)₂D). (a) Vitamin D is produced when ultraviolet (UV) rays from the sun strike the skin and can also be obtained from leafy vegetables, dairy products, fish, and vitamin D fortified foods. (b) Vitamin D is converted in the liver to calcidiol, or 25-hydroxyvitamin D (25(OH)D). (c) Then, calcidiol travels to the kidneys and becomes enzymatically converted to calcitriol, also known as 1,25-dihdrydroxyvitamin D (1,25(OH)₂D).