What is it for
By vitamin D, in its forms of vitamin D2 and vitamin D3, we mean those vitamins that have an action against rickets, or a serious disease of children that causes mental retardation and ossification disorders.
It is known that the main function of vitamin D is that carried out at the level of the bones; in fact, it favors the deposition of calcium in the bone tissue, a supporting connective tissue characterized by considerable hardness and resistance. In fact, severe deficiencies of vitamin D cause diseases such as osteomalacia and osteoporosis in adults, characterized mainly by weak bones.
Vitamin D also regulates the absorption of the minerals calcium, magnesium and phosphorus from foods present in the intestine. These minerals, in addition to being components of the bones, regulate the osmotic balance of our body, favor intercellular communications, regulate the pH of extracellular fluids.
Less known to the public is the function of vitamin D on the immune system, it determines the growth and formation of macrophages starting from myeloid precursors, inhibits the synthesis of immunoglobulins and stimulates platelet aggregation. Although they have not yet been confirmed by scientific evidence, some studies hypothesize that the administration of vitamin D in patients infected with the Covid 19 virus would lead to a decrease in the inflammatory response and an improvement in the clinical picture of the infected.
Both vitamin D2 and vitamin D3 are inactive forms that require bioactivation to be transformed into the active compound calcitriol by liver and kidney enzymes to carry out vitamin activity. In humans, the main compounds taken through food that will undergo enzymatic bioactivation are vitamin D2 (or ergocalciferol) and vitamin D3 (or cholecalciferol); vitamin D3 will be, after bioactivation, 80-100 times more active than vitamin D2.
Both vitamins D2 and D3 taken with food are transformed into the prehormone calcidiol (25-hydroxycholecalciferol), which in turn is transformed by the same liver and kidney enzymes into the active hormone calcitriol (1,25-dihydroxycalciferol or 1,25- (OH)2D). The latter penetrates the cell membranes of target cells and interacts with its own receptors located near the cell nucleus, activating them.
There is another very important biosynthetic way through which man synthesizes vitamin D: through exposure to sunlight. In detail, this synthesis pathway originates from provitamin dehydrocholesterol, a chemical compound similar in molecular structure to cholesterol, since it is derived from it. Dehydrocholesterol is one of the components of our skin and is transformed into cholecalciferol (vitamin D3) by the action of the sun's UV rays.
Please note: to promote a significant endogenous production of vitamin D it is necessary to expose the 70-80% of the skin surface for about 30-40 minutes to the sun.
Interestingly, there are conditions that limit vitamin D biosynthesis:
- shortness of sunshine hours (winter months),
- use of sunscreens (e.g. sunscreens),
- increased pigmentation of melanin,
- poor sun exposure,
- obliquity of the sun's rays (winter period),
- presence of smog with consequent reduction of the penetration of UV rays.
Sources of vitamin D.
The foods richest in vitamin D are liver, fish oils, some marine fish (herring, salmon, sardine). Smaller quantities are present in eggs, butter and milk.
Daily requirement of vitamin D
According to Regulation (EU) No. 1169/2011 of the European Parliament and of the Council of 25 October 2011, the recommended consumption of vitamin D is 5 mg of vitamin D. Under normal conditions, good exposure to the sun and a varied diet is sufficient to satisfy the body's needs for calciferol. However, the doctor can prescribe vitamin D and Calcium food supplements, antioxidant supplements or drugs (Dibase® or Didrogyl®) in case of vitamin deficiency or in case of the presence of risk factors.
Vitamin D deficiency
Vitamin D deficiency is the clinical condition resulting from the absence of appropriate levels of vitamin D in the body. According to Harvard University, vitamin D deficiency affects approximately one billion people worldwide.
The diagnosis of vitamin D deficiency is performed with a blood test, in more detail the prehormone calcidiol is searched for by blood volume:
|Condition||Concentration in nmol / l||Concentration in ng / ml|
|Shortage||<30 nmol / l||<12 ng / ml|
|Insufficiency||Between 30 nmol / l and 75 nmol / l||Between 12 ng / mL and 30 ng / mL|
|Normality||Between 75 nmol / L and 200 nmol / L||Between 30 ng / mL and 80 ng / mL|
|Excess||> 200 nmol / l||> 80 ng / ml|
|Toxicity||> 375 nmol / l||> 150 ng / ml|
Causes of deficiency:
Vitamin D deficiency can be caused by:
- insufficient intake with food;
- poor sun exposure;
- impaired intestinal absorption capacity;
- liver and kidney diseases that compromise the production of enzymes responsible for the bio-activation of vitamin D;
- use of drugs such as cholestyramine, glucocorticoids, antifungals, antivirals, anti-rejection drugs etc ... that compromise the normal metabolism of vitamin D.
There are also risk factors associated with a greater risk of developing vitamin D deficiency; among the main ones:
- obesity: vitamin D, being similar to fatty tissues, is sequestered by the latter, with a reduction in bioavailability;
- cigarette smoking and alcoholism: impaired enzymatic metabolism of vitamin D;
- advanced age: the skin, with increasing age, progressively loses its ability to produce vitamin D;
- Crohn's disease or celiac disease: impaired intestinal absorption of vitamin D;
- Babies who are breastfed for a long time may be deficient in vitamin D, as breast milk is a scarce source.
Deficiency symptoms and associated diseases
Vitamin D deficiency is a devious condition. However serious deficiencies can show a symptomatic picture characterized by:
- pain in bones, joints and muscles;
- recurrent fatigue;
- brittle bones that tend to deform;
- neurological disorders (difficulty thinking clearly).
Vitamin D deficiency impairs bone mineralization in different ways, which contributes to the development of diseases such as rickets in children and osteomalacia and osteoporosis in adults. However, recent studies associate vitamin D deficiency with diseases such as diabetes, hypertension, metabolic syndrome and dyslipidemia.