Vitamin D

In the thirties of the XX century, vitamin D was first synthesized and studied. This vitamin is very interesting to the world of science, since it is both a vitamin and a hormone. It can enter the body both with food and can be produced by the body when exposed to sunlight. Vitamin D is known as a vitamin, associated with the development of rickets. The mention of rickets occurs back in 1650. The vitamin model was proposed in 1919, synthesized in 1932.

What you need to know about vitamin D?

In order not to get into a dead end, when to you scientific terms are called this or that substance, you need to know its chemical name. Here, in vitamin D, for example, other names sound like an anti-rosic vitamin, cholecalcefirol, ergocalciferol and wheosterol.

Vitamin D is divided into several vitamins of this group. So, vitamin D3 is called cholecalcefirol, and simply vitamin D is ergocalciferol. Both these vitamins can be contained in food only animal species. Also, vitamin D is produced directly by the body, and this is due to the effects of ultraviolet rays on the skin.

Vitamin D is directly associated with a disease such as rickets. The fact is that animal fats can excrete vitamin D if they are exposed to sunlight. Thus, as early as 1936, pure vitamin D was isolated from the fat of tuna. So it was used to combat rickets.

The chemical nature and biologically active forms of vitamin D

Vitamin D - the group designation of several substances related to the chemical nature of sterols. Vitamin D is a cyclic unsaturated high molecular weight alcohol ergosterol.

There are several vitamins of vitamin D. Among them, the most active are ergocalciferol (D2), cholecalciferol (D3), dihydroergocalcalorol (D4). Vitamin D2 is formed from a plant precursor (provitamin D) - ergosterol. Vitamin D3 - from 7-dehydrocholesterol (synthesized in human and animal skin) after irradiation with ultraviolet light. Vitamin D3 is biologically the most active.

Less active vitamins of vitamin D - D4, D5, D6, D7 - are formed by irradiation with ultraviolet plant precursors (respectively dihydroergosterol, 7-dehydrositosterol, 7-dehydro-stigmasterol and 7-dehydrocampesterol). Vitamin D1 is not found in nature. Biologically active forms of ergo- and cholecalciferol are formed during metabolism.

Metabolism of Vitamin D

Nutritional calciferols are absorbed in the small intestine with the participation of bile acids. After absorption, they are transported in the composition of chylomicrons (60-80%), part in a complex with os2-glycoproteins in the liver. Here, endogenous cholecalciferol also enters the blood.

In the liver in the endoplasmic reticulum, cholecalciferol and ergocalciferol undergo hydroxylation with 25-hydroxylase of cholecalciferol. As a result, 25-hydroxy-cholecalciferol and 25-hydroxyergocalcalifer are formed, they are usually considered the main transport form of vitamin D. They are transferred to the blood with the blood as a special calciferol-binding protein of the plasma to the kidneys, where 1,25-hydroxylase is formed with the participation of the enzyme 1-a-hydroxylase of calciferols, dihydroxycalciferols. They are an active form of vitamin D, which has a D-hormone-like action - calcitriol, which regulates the exchange of calcium and phosphorus in the body. In humans, vitamin D3 is more effective in increasing serum 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D levels than vitamin D2.

In cells, vitamin D3 is localized in membranes and subcellular fractions - lysosomes, mitochondria, nucleus. In tissues, vitamin D does not accumulate, with the exception of adipose tissue. Both 25-hydroxyvitamin D and 1,25-dihydroxyvitamin D decay catalyzed by the enzyme 24-hydroxylase. This process occurs in various organs and tissues. In general, the amount of vitamin D circulating in the blood depends on exogenous sources (foods, nutraceuticals), endogenous production (synthesis in the skin), and the activity of enzymes involved in the metabolism of the vitamin.

It is excreted mainly with feces in unchanged or oxidized form or in the form of conjugates.

Biological functions of vitamin D

The biological activity of 1,25-hydroxycalciferols is 10 times higher than the activity of the initial calciferols. The mechanism of action of vitamin D is similar to the action of steroid hormones: it penetrates into the cell and regulates the synthesis of specific proteins by action on the genetic apparatus.

Vitamin D regulates the transport of calcium and phosphorus ions through cell membranes and thereby their level in the blood. It acts as a synergist with parathyroid hormone and as an antagonist with thyrotoxicotropic hormone. This regulation is based on at least three processes involving vitamin D:

1. Stimulates the absorption of calcium and phosphate ions through the epithelium of the small intestine mucosa. Calcium absorption in the small intestine occurs by facilitated diffusion with the participation of a special calcium-binding protein (CaCB-calbindine D) and active transport with Ca2 + -ATPase. 1,25-Dihydroxycalciferols induce the formation of CaSB and protein components of Ca2 + -ATPase cells of the small intestinal mucosa. Calbindine D is located on the surface of the mucous membranes and, thanks to its high ability to bind Ca2 +, facilitates its transport inside the cell. In the bloodstream from the cell, Ca2 + comes with the participation of Ca2 + -ATPase.
2. Stimulates (together with parathyroid hormone) the mobilization of calcium from bone tissue. The binding of calcitriol to osteoblasts increases the formation of alkaline phosphatase and the Ca-binding protein of osteo-calcina, also facilitates the release of Ca + 2 from the deep apatite layers of the bone and deposition of it in the growth zone. At high concentrations, calcitriol stimulates the resorption of Ca + 2 and inorganic phosphorus from the bone, acting on osteoclasts.
3. It stimulates the reabsorption of calcium and phosphorus in the renal tubules, due to stimulation of renal tubules by vitamin D Ca2 + -ATPase. In addition, in the kidney calcitriol suppresses its own synthesis.

In general, the effect of vitamin D is expressed in an increase in the content of calcium ions in the blood.

[1], [2], [3], [4]

How much vitamin D is needed per day?

The dose of vitamin D increases, depending on the age of the person and his waste of this vitamin. So, children should consume 10 micrograms of vitamin D per day, adults - the same amount, and people of advanced age (after 60ty years) - about 15 micrograms of vitamin per day.

When does the need for vitamin D increase?

People in old age are better to increase the daily dose of vitamin D, the same applies to people who are almost never in the sun. To prevent rickets, vitamin D should be taken to children. Women during pregnancy and women breastfeeding, as well as during menopause need to increase the intake of this vitamin.

Digestibility of Vitamin D

With the help of bile juices and fats, vitamin D is absorbed in the stomach better.

[5], [6], [7], [8]

Interaction of vitamin D with other elements of the body

Vitamin D helps to absorb calcium (Ca) and phosphorus (P), and with its assistance, magnesium (Mg) and vitamin A are well absorbed.

What determines the presence of vitamin D in food?

You do not have to worry about the proper preparation of foods, because during the thermal treatment vitamin D is not lost, but such factors as light and oxygen can completely destroy it.

Why there is a shortage of vitamin D?

Digestibility of the vitamin may be affected by poor liver function (liver failure and mechanical jaundice), as the supply of the right amount of bile is severely impaired.

Since vitamin D is produced in the human body with the help of exclusively skin and sunlight (the fat on the skin synthesizes with the production of vitamin D under the influence of the sun, and then the vitamin is absorbed into the skin again), then you can not go to the shower immediately after sun exposure. Otherwise, you will wash away the entire vitamin D from the skin, which will cause its deficiency in the body.

Symptoms of vitamin D deficiency

In young children, with a lack of vitamin D, sleep can be disturbed, sweating may increase, the teeth may be cut, the bone tissue of the ribs, limbs and spine may soften. Children become irritable, their muscles relax, and babies can overgrow the fontanel for a long time.

In adults, the symptoms of vitamin deficiency are slightly different: although they also soften the bones, such people can still lose weight and suffer from severe fatigue.

Products that contain vitamin D

If you eat more foods rich in vitamin D, you can fully maintain the amount of this vitamin needed in the body. Such products include liver (0.4 μg), butter (0.2 μg), sour cream (0.2 μg), cream (0.1 μg), chicken eggs (2.2 μg) and sea bass (2.3 μg vitamin D). Use these foods more often so that your bones and the body as a whole are safe!

Vitamin D is found in a number of products of animal origin: in the liver, butter, milk, as well as in yeast and vegetable oils. The most rich in vitamin D is the liver of fish. It produces fish oil, used for the prevention and treatment of D-vitamin deficiency.

Signs of excess dose of vitamin D

With an overdose of vitamin D, nausea, diarrhea, colic in the abdomen, severe fatigue, headaches may occur. People who suffer from vitamin D supersaturation often have very itchy skin, their heart and liver work is disrupted, blood pressure can rise and eyes become inflamed.

Treatment of hypervitaminosis D:

• drug cancellation;
• a diet low in Ca2 +;
• consumption of large quantities of liquid;
• the appointment of glucocorticosteroids, a-tocopherol, ascorbic acid, retinol, thiamine;
• In severe cases, intravenous administration of large amounts of 0.9% NaCl solution, furosemide, electrolytes, hemodialysis.