Why vitamin D is beneficial for the immune system

Vitamin D seems to be an important ally of the immune system: ensuring adequate levels can help protect yourself during the cold months.

Not only vitamin C and zinc. When the good functionality of the immune system is at stake, the essential micronutrients, including vitamins and minerals, that must be constantly supplied to the body are many more and all, in various ways, indispensable.

Research conducted in recent years has indicated that, among the substances that help protect against infectious diseases and appropriately modulate the immune response, vitamin D plays a key role: it is a compound known mainly for its role in the regulation of bone metabolism, but in reality it is implicated in countless fundamental physiological processes, often unsuspected for non-experts and, in many cases, still not fully understood even by doctors and researchers.

The immune system and vitamins

Decades of studies have shown that an adequate supply of vitamins and minerals is necessary to support both the innate immune response (present from birth and consisting of real “barriers”, such as the skin and mucous membranes, protective secretions such as gastric acid and bronchial mucus, immune cells of various types such as monocytes, macrophages, neutrophils and other white blood cells), and the “adaptive” or “acquired” one (which develops over time and sees among the protagonists essentially the B lymphocytes, or the cells of the immune system responsible for the production of antibodies, and T lymphocytes).

The micronutrients for which, to date, the greatest evidence has been collected in favor of an activity to support the body’s defense systems are vitamin D, antioxidant vitamins C, A and E, some B vitamins (in particular, folic acid, B6 and B12), iron, selenium, copper and zinc.

Importance of vitamin D in the immune system

For some years now, medicine has discovered that vitamin D participates in many key processes in the body, the best known of which is the metabolism of calcium and phosphate. Vitamin D is in fact essential for the achievement and maintenance of adequate bone mass and for the prevention of rickets in children and osteoporosis, fractures and bone pain that follow in adults.

For example, vitamin D deficiencies have been associated with an increased risk of cardiovascular disease and diabetes, certain cancers (such as colon cancer, breast cancer in women, and prostate cancer in men), mood disorders (especially depression) and cognitive decline in old age.

A further favorable role of vitamin D, scientifically recognized only recently, but in reality exploited for decades unconsciously in respiratory medicine, concerns the ability of this compound to modulate the activity of the immune system:

– promoting it, when it is necessary to counteract infections

– attenuating it, when it is excessive and gives rise to chronic inflammatory or autoimmune diseases.

The confirmation that vitamin D can exert these immunoregulatory activities came from the presence of receptors capable of binding its metabolite 1,25 (OH) 2D on numerous cells of the immune system, such as monocytes, macrophages and thymus cells (small organ present in the center of the chest in which the maturation of T lymphocytes takes place).

In addition, it has been found that 1,25(OH)2D is able to stimulate the production of powerful antimicrobial compounds by both some cells of the immune system and the cells of the epithelium lining the respiratory tract, thus playing an action of prevention of infections of the nose, throat, bronchi and lungs.

These findings have made it possible to explain, on the one hand, why children with vitamin D deficiency are more predisposed to respiratory infections and, on the other, why exposure to UV B rays and the administration of cod liver oil (two excellent sources of vitamin D3) are able to reduce the incidence of colds and flu, as well as to promote healing from bacterial tuberculosis.

Sources of vitamin D

The main natural source that allows to obtain adequate amounts of vitamin D is the biosynthesis by the skin exposed to sunlight (UV B rays), possible only at certain times of the year and at certain latitudes. Pollution, clothing and the use of sunscreens can interfere by reducing or blocking the synthesis of this vitamin.

Nutrition is to a lesser extent a source of vitamin D and there are few foods that contain it in appreciable quantities. These are essentially foods of animal origin, which tend to be rich in lipids, such as fatty fish (salmon, herring, mackerel, tuna, etc.) and cod liver oil (traditional remedy against rickets), beef or pork liver, eggs and cheese. Even some mushrooms grown under a light containing a high proportion of UV B rays may contain appreciable amounts of this vitamin.

Contrary to what many people think, however, milk contains little vitamin D (unless it is specifically enriched) and loses almost all of it if it is treated at high temperature (UHT) to prolong its preservation or boiled before being drunk (vitamin D is thermolabile and is destroyed by heat). Therefore, to supplement the diet, it is better to consume fresh milk, with added vitamin D and calcium, at room temperature or lukewarm.

Vitamin D deficiency

Despite its universally recognized importance for the health of the organism and the benefits it can bring at multiple levels and at all stages of life, situations of insufficiency, deficiency and deficiency of vitamin D continue to be widely spread globally, even in countries characterized by good standards of general nutrition such as Western Europe (including Italy) and the United States.

This exposes a large proportion of adults and children to a range of dysfunctions and diseases that could easily be avoided through the combination of appropriate sun exposure, a diet richer in foods containing appreciable amounts of vitamin D and the intake of targeted supplements (the dosage of which must be established according to individual needs), which are often indispensable, especially in pediatric age and in the elderly.

To find out if you have adequate vitamin D, you have to measure the level in your blood of one of its metabolites: 25(OH)D. Although there is not complete agreement on the ideal values to be considered, the following reference ranges are currently considered valid:

To be exposed to an increased risk of developing vitamin D insufficiency or deficiency are:

– the elderly, especially if they live in long-term care facilities;

– people with dark skin (which produces vitamin D less efficiently when exposed to the sun);

– people who do not spend enough time in the fresh air;

– people with gastrointestinal or metabolic diseases (which interfere with the absorption or metabolism of vitamin D)

– children and adults who are obese or severely overweight (because vitamin D is “sequestered” by body fat);

– people on medication that alter intestinal absorption or vitamin D metabolism.

Low levels of vitamin D are more frequent and likely in the autumn and winter months, when the microorganisms responsible for colds are more widespread and aggressive. Vitamin D-enriched foods and/or supplements between autumn and early spring can therefore be particularly beneficial.