Vitamins are compounds that must be provided with the diet, as the body cannot synthesise them in sufficient quantities. The body’s nutritional status is fundamental to maintaining normal immune system function, and nutrient deficiencies often result in impaired immune function. Consuming vitamins at higher levels than the recommended daily norm can further strengthen the immune system. This also applies to vitamins A, D, E, K, which are fat-soluble compounds.
The role of vitamin A in building immunity
Vitamin A is found in offal (liver), butter, eggs and in the form of carotenoids (provitamin A) in vegetables and fruit. This vitamin exists in the form of retinol, retinal and retinoic acid (RA), of which the latter is the most important biologically active metabolite.
Retinoic acid is essential for strengthening the innate immune response and regulating acquired immunity. Retinol influences cytokine production, cell integrity, immune cell activation, antigen presentation and lymphocyte transport to mucosal surfaces (including the gut). Retinoic acid promotes the differentiation of immunoglobulin A (IgA), with antiviral and antimicrobial properties, by antibody-secreting cells (ASCs) present in mucosal tissues. Vitamin A also regulates the antimicrobial activity of macrophages. It also influences the composition and diversity of the gut microbiota, which is involved in the preparation and regulation of mucosal and systemic immunity. In addition, vitamin A and its metabolites modulate the balance between Th1 and Th2 cells, which plays an important role in allergies and autoimmune diseases.
The role of vitamin D in building immunity
Vitamin D (calcitriol, cholecalciferol) mainly comes from skin synthesis and supplementation is recommended for people of all ages during autumn and winter. Vitamin D has its own receptors (VDR) in the human body, which are responsible for the expression of as many as 2,000-3,000 genes, allowing it to have a versatile action in many organs and cells of the immune system. Calcitriol influences many factors of the innate and acquired immune system. It exerts antiviral and antimicrobial activity by stimulating the release of cathelicidin and defensins. It also reduces the production of pro-inflammatory cytokines and is essential in the immunomodulation of immune cells.
The role of vitamin E in building immunity
Vitamin E is otherwise a collective term for the four tocopherols and tocotrienols (α-, β-, γ- and δ-) found in foods. The best sources of it are vegetable fats (sunflower oil, wheat germ oil, olive oil), seeds and nuts.
Vitamin E directly affects the integrity of the cell membrane of immune T cells, signal transduction and cell proliferation. It has protective properties against the oxidation of polyunsaturated fatty acids, which are present in the membranes of immune cells. Their high metabolic and defence activity against pathogens makes them susceptible to oxidative damage. Vitamin E modulates inflammatory mediators, including PGE2 and cytokine production, so it also indirectly affects immunity.
Vitamin E supplementation above standard dietary recommendations has been shown to improve immune function and reduce the risk of infection, especially in older people.
The role of vitamin K in building immunity
Vitamin K is divided in nature into two subgroups: vitamin K1 (phylloquinone) and the vitamin K2 group (menaquinone – MK). Sources of menaquinone are animal products and fermentation of capable bacteria in food, including gut bacteria. Vitamin K-dependent activation of matrix Gla protein (MGP) is a potent protective factor for soft tissues against various injuries, such as mineralisation and degradation. It protects against vascular and pulmonary tissue damage caused by inflammation during SARS CoV-2 infection, among others. In addition, K2-MK7 inhibits pro-inflammatory mediators such as IL-1α, IL-6, IL-1β and TNF-α.
Synergism of vitamins A, D, E, K
Deficiencies of both vitamin A and vitamin D promote the emergence of a dysbiosis of the microbiome, which increases susceptibility to infection or damage to the digestive tract. They regulate the function of the immune cells of the intestinal epithelium and mucous membranes. Calcitriol, on the other hand, works in tandem with K2-MK7 to support the absorption of calcium first in the intestines and then its transport to the bones. Vitamin E, on the other hand, is a powerful antioxidant, protecting immune cells from damage, among other things. A deficiency in any of these vitamins will weaken the immune system.
Effect of vitamin A, D, E, K deficiency on immunity
Retinol deficiency causes a number of consequences: imbalances in the production of inflammatory and immunomodulatory cytokines, impaired mucosal barrier function, intestinal inflammation and disruption of the gut microbiome. In contrast, infectious diseases adversely affect the status of vitamin A in the body, interfering with its intestinal absorption, utilisation and excretion. This may indicate a greater need for supply of this component during infection. Vitamin D deficiency leads to immune system dysfunction, which increases the risk of contracting bacterial and viral infections. Vitamin E deficiency also increases the risk of infection and the appearance of inflammation in the body.
What to look for when choosing vitamins A, D, E, K?
The main factor that affects the adequate absorption of these nutrients is the presence of fat, so opting for oil-containing capsules or drops will be advisable. Chemical forms also make a difference. It is important to choose vitamin D3 of natural origin. In the instance of menaquinone, the best absorbed form is MK-7, derived from natto. Vitamin E often appears in preparations as a single form (e.g. D-alpha tocopherol), and the body needs a full profile of tocopherols and tocotrienols.
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