Vitamin D, a steroid hormone, is essential for maintaining a healthy immune system. In mid-latitude countries such as the UK, people with pale skin can make enough of it during summer by exposing bare arms or legs to sunlight for a few minutes a day.

The process takes longer in those with heavily pigmented skin that blocks more ultraviolet radiation from the sun. In winter all of a person’s vitamin D has to come from foods, such as oily fish, egg yolks and mushrooms, or pills

.https://www.google.com/amp/s/amp.ft.com/content/932920f9-f9ae-414a-940f-602169ee620f

Vitamin D is crucial to activating our immune defenses and that without sufficient intake of the vitamin - the killer cells of the immune system -- T cells -- will not be able to react to and fight off serious infections in the body. The research team found that T cells first search for vitamin D in order to activate and if they cannot find enough of it will not complete the activation process.

https://www.sciencedaily.com/releases/2010/03/100307215534.htm

Hi,

The vitamin D receptor is expressed on immune cells (B cells, T cells, and antigen-presenting cells) and these immunologic cells are all are capable of synthesizing the active vitamin D metabolite, vitamin D has the capability of acting in an autocrine manner in a local immunologic milieu.

Article Vitamin D and the Immune System

Vitamin D is called as defence vitamin because it activates our immune defenses.

Article Vitamin D controls T cell antigen receptor signaling and act...

vit D improve the activity of immune system

Vitamin D, is a defensive vitamin because, it play key roles on the human immune response to infections. It induces the production of the antimicrobial polypeptide cathelicidin(hCAP18/LL37), which has both antibacterial and antiviral effects. Additionally, in the host defense mechanism, it is also involve in the regulation of autophagy, regulation of pathways involves in oxidative stress, regulation of secretion of proinflamatory cytokines and chemokines, and stabilization of the endothelium. More recently, vitamin D status has been shown to be important in host-microbiome interactions in both respiratory and intestinal compartments.

Very important given a Vitamin D deficiency is documented as beeing associated, among others, with reduced lymphocytes in number, slow differentiation of monocytes to macrophages and lower phagocytic ability of same macrophages, thus increasing infections' incidence and severity ! That is immunitary defence enough, to us ! :) We are on a Vitamin D status populational snap evaluation here in Montréal right now ! Just like in many Northern countries, the preliminary data are pointing on mild to high insuficiency ! We are still compiling the data , but if the general picture is consistent, even if not severe deficiency, that would still be a serious public health problem under present viral pandemia circumstances , amid both: the COVID incidence and it's prognostic outcomes! Best, DCM

Scientists have found that vitamin D is crucial to activating our immune system. Insufficient intake of the D vitamin, - the killer cells of the immune system such as T cells will not be enable to react to and fight off serious infections in the body.

Vitamin D is recognized as effective in support of immunity of the trach/bronch tree..

Dear colleagues, wishing ...a Better New Year 2021 !

Our research team has just released the numbers of our vitamin D clinical snap shot survey in Montréal :

Preprint Vitamin D homeostasis in obese and diabetic groups, potentia...

In regard to the COVID-19 immunity challenge, the need for a vitamin D supplementation seem to be obvious.

Best, DCM

I fully agree with Arvind Singh's previous answers, see also

Article Immunologic Effects of Vitamin D on Human Health and Disease

or papers like http://www.businessworld.in/article/Vitamin-D-Defense-The-Best-Immunity-Booster/20-04-2020-189615/