What is Vitamin D?
A Pro-hormone
Vitamin D, also known as “calciferol,” is a pro-hormone. Thus, it is the precursor of the hormone calcitriol which increases calcium absorption.
This is why it is primarily known for its role in bone growth.
This vitamin is naturally produced by the body. It is synthesized by the skin under the action of UVB rays.
In addition to sun exposure, it is also obtained through diet and/or supplementation. There are 2 types of vitamin D:
- D2 or ergocalciferol of plant origin
- D3 or cholecalciferol found in animal meat.
Among foods rich in vitamin D, we can mention cod liver oil, fatty fish, eggs, dairy products, and mushrooms.
A Major Role in Immunity
Beyond its importance for bone health, it is also essential for the immune system. Many studies have thus confirmed the link between vitamin D and immunity.
In this regard, the EFSA (European Food Safety Authority) authorizes the health claim: “Vitamin D contributes to the normal functioning of the immune system.”
This fat-soluble vitamin circulates in the blood. Its receptors are present in almost all cells of the body. They are capable of regulating certain processes, activating or deactivating them.
They notably modulate the expression of HLA genes involved in immunity. Thus, vitamin D contributes to a healthy and functional immune response.
Moreover, it stimulates the body’s defense capacity against assaults and pathogens.
This is why a vitamin D deficiency results in a greater susceptibility to diseases and infections. Supplementation may therefore be necessary and beneficial in winter.
Read also | How to choose the best vitamin D?
Its Benefits on the Immune System
It Activates Immune Defenses
Vitamin D stimulates the body’s immune defenses and notably T lymphocytes (white blood cells). Thus, these killer cells are better able to fight bacteria, viruses, and other infections.
This study, for example, confirms its value against acute respiratory infections: rhinitis, bronchitis, pneumonia…
In case of vitamin D deficiency, these white blood cells enter a dormant phase. Vitamin D mobilizes them and rekindles the immune response.
It also activates the expression of the enzyme PLC-gamma 1 (phospholipase C gamma 1 protein). It helps the cell deliver a suitable response depending on the pathogen.
Finally, it stimulates dendritic cells. These cells detect infectious agents, capture the antigen, and alert T lymphocytes.
As shown in this study, vitamin D regulates the maturation of dendritic cells corresponding to the moment when the cell detects the pathogen and activates.
It Supports Adaptive and Innate Immune System
As shown in this study, vitamin D supports the adaptive immune system and the innate (or acquired) immune system.
Innate immunity acts immediately in the event of an attack. It quickly defends the body by mobilizing cells and activating various mechanisms. It is the first line of defense.
Adaptive immunity, on the other hand, offers a later but lasting response. It consists of T and B lymphocytes. It targets the infectious agent and retains the antigen in memory. It ensures an increasingly effective and targeted immune response.
On one hand, vitamin D aids first-line defenses like macrophages. It also increases the number of neutrophils, other white blood cells that support macrophages.
On the other hand, it supports adaptive immunity T-type cells as shown in this study. Moreover, it increases the number of Th2 lymphocytes that fight against parasites.
Finally, according to this study, it even prevents a possible overreaction of the immune system in case of Covid19 infection.
It supports the elimination of pathogens
In addition to acting upstream and stimulating the immune system, it also supports mechanisms for eliminating pathogens.
For this, and as shown by this study, it promotes the synthesis of antimicrobial peptides by immune cells. These agents intervene during the innate response.
These include cathelicidin and defensins. They are capable of penetrating and altering the membranes of viruses to better destroy and eliminate them.
