Vitamin of D3 (calciferol) 2936290000
Vitamins of group D are formed under the action of ultraviolet radiation in tissues of animals and plants from sterols.
Vitamins of group D are:
- vitamin D 2 - ergocalciferol; isolated from yeast, its provitamin is ergosterol;
- vitamin D 3 - cholecalciferol; isolated from animal tissues, its provitamin - 7-dehydrocholesterol;
- vitamin D 4 - 22, 23-dihydro-ergocalciferol;
- vitamin D 5 - 24-ethylcholecalciferol (sitocalciferol); isolated from wheat oils;
- vitamin D 6 - 22-dihydroethylcalciferol (stigma-calciferol).
Today vitamin D is called two vitamins - D 2 and D 3 - ergocalciferol and cholecalciferol - these are colorless and odorless crystals, resistant to high temperatures. These vitamins are fat-soluble, i.e. they are soluble in fats and organic compounds and insoluble in water.
The activity of vitamin D preparations is expressed in international units (ME): 1 ME contains 0.000025 mg (0.025 mgc) chemically pure vitamin D. 1 mcg = 40 IUparsley
Vitamin D is formed in the skin under the influence of sunlight from provitamins. Pro-vitamins, in turn, partly enter the body in ready-made form from plants (ergosterol, stigmasterol and sitosterol), and partly are formed in the tissues of their cholesterol (7-dehydrocholesterol (provitamin D 3 ).
Provided that that the body receives a sufficient amount of ultraviolet radiation, the need for vitamin D is fully compensated. However, the amount of vitamin D synthesized by sunlight depends on factors such as:
- the wavelength of light (the most effective is the average wavelength spectrum that we get in the morning and at sunset); ;
- initial skin pigmentation and (the darker the skin, the less vitamin D is produced by sunlight);
- age (aging skin loses its ability to synthesize vitamin D);
- the level of air pollution (industrial emissions and dust do not transmit the spectrum of ultraviolet rays, potentiating the synthesis of vitamin D, this explains, in particular, the high prevalence of rickets in children, living in Africa and Asia in industrial cities).
Additional food sources of vitamin D are dairy products, fish oil, egg yolk. However, in practice, milk and dairy products do not always contain vitamin D or contain only trace (insignificant) amounts (for example, 100 g of cow's milk contains only 0.05 mg of vitamin D), so their consumption, unfortunately, cannot guarantee coverage of our needs for this vitamin. In addition, milk contains a large amount of phosphorus, which interferes with the absorption of vitamin D.
The main function of vitamin D is to ensure normal growth and development of bones, prevent rickets and osteoporosis. It regulates mineral metabolism and promotes the deposition of calcium in bone tissue and dentin, thus preventing osteomalacia (softening) of bones.
When entering the body, vitamin D is absorbed in the proximal region small intestine, and always in the presence of bile. Part of it is absorbed in the middle parts of the small intestine, a small part in the ileum. After absorption, calciferol is found in the composition of chylomicrons in free form and only partially in the form of ether. Bioavailability is 60-90%.
Vitamin D affects the general metabolism during the metabolism of Ca2 + and phosphate (HPO2-4). Primarily, it stimulates the absorption of calcium, phosphates and magnesium from the intestine. An important effect of the vitamin in this process is to increase the permeability of the intestinal epithelium for Ca2 + and P.
Vitamin D is unique - it is the only vitamin that acts both as a vitamin and as a hormone. As a vitamin, it maintains the level of inorganic P and Ca in the blood plasma above the threshold value and increases the absorption of Ca in the small intestine.
The active metabolite of vitamin D - 1 acts as a hormone. 25-dioxycholecaciferol, produced in the kidneys. It affects the cells of the intestine, kidneys and muscles: in the intestine it stimulates the production of a carrier protein necessary for the transport of calcium, and in the kidneys and muscles it enhances the reabsorption of Ca ++.
Vitamin D 3 influences the nuclei of target cells and stimulates the transcription of DNA and RNA, which is accompanied by an increase in the synthesis of specific proteids.
However, vitamin D's role is not limited to bone protection, it affects the body's susceptibility to skin diseases, heart disease and cancer. In geographical areas where food is poor in vitamin D, the incidence of atherosclerosis, arthritis, diabetes, especially juvenile diabetes is increased.
It prevents muscle weakness, increases immunity (vitamin D level in the blood serves as one of the criteria for assessing the life expectancy of AIDS patients), tanned people), the synthesis of vitamin D in the skin is reduced. The same can be said for older people (their ability to convert provitamins into vitamin D is halved) and those who follow a vegetarian diet or eat insufficient amounts of fat.
Disorders of the intestines and liver, gallbladder dysfunction negatively affect the absorption of vitamin D.
In pregnant and lactating women, the need for vitamin D increases, because an additional amount is needed to prevent rickets in children.
Symptoms of hypovitaminosis
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Vitamin D 2 (ergocalciferol) is prescribed for pregnant women for women to prevent rickets in children at 30-32 weeks of pregnancy in fractional doses for 10 days, for a total of 400,000-600,000 ME; breastfeeding mothers - 500 IU daily from the first days of feeding until the start of the drug use in a child.
In order to prevent rickets, children are given ergocalciferol from the age of three weeks, the total dose per course - 300,000 ME. < therefore, overdose can cause serious problems.
Since vitamin D increases blood calcium levels, excessive intake of it can lead to excess calcium concentration. In this case, calcium can penetrate into the walls of blood vessels and provoke the formation of atherosclerotic plaques. This process can be accelerated when there is a deficiency in the body of magnesium.
Vitamin D preparations are contraindicated in such diseases as:
- pulmonary tuberculosis (active forms),
- gastric ulcer and duodenum, <