What is the function of vitamin D?

Vitamin D is a nutrient element needed by the human body, and it is very important in the human body. It can prevent physical diseases and is good for the body. Vitamin D can combine with the blood in the human body to form some nutrients for the human blood. The vitamin D in food can also be absorbed with fat, mainly into the human intestine.

What does vitamin D do?

Vitamin D, a steroid derivative, has anti-rickets effects and is also known as anti-rickets vitamin.

It is currently believed that vitamin D is also a steroid hormone. The most important members of the vitamin D family are VD2 (ergocalciferol) and VD3 (cholecalciferol). Vitamin D is a derivative of different vitamin D precursors after ultraviolet irradiation. Plants do not contain vitamin D, but provitamin D exists in both animals and plants. Vitamin D is a fat-soluble vitamin with five compounds, of which vitamin D2 and vitamin D3 are more closely related to health. They have the following three characteristics: it exists in some natural foods; the human body stores 7-dehydrocholesterol produced from cholesterol under the skin, which can be converted into vitamin D3 after being exposed to ultraviolet rays. Proper sunbathing is sufficient to meet the body's needs for vitamin D.

Chemical structure

Vitamin D (Vd) is a cyclopentanepolyhydrophenanthrene compound, which can be formed by provitamin D by activation of ultraviolet rays at 270~300nm. 7-dehydrocholesterol under the skin of animals and ergosterol in yeast cells are both provitamin D. They are converted into small amounts of vitamin D3 and vitamin D2 respectively after activation by ultraviolet rays, but those exposed to artificial radiation are mostly of this type. The maximum absorption peak of vitamin D is 265nm. It is relatively stable and soluble in organic solvents. Light and acid promote isomerization. It should be stored in a cold environment without nitrogen, light and acid. The oil solution is stable after adding antioxidants, and the aqueous solution is unstable due to dissolved oxygen. Double bond system reduction may also result in loss of biological effectiveness.

Physiological metabolism

Vitamin D obtained from food is absorbed together with fat, and the main absorption sites are the jejunum and ileum. Bile helps with its absorption. When fat absorption is disturbed, such as chronic pancreatitis, steatorrhea and bile duct obstruction, its absorption will be affected. Absorbed vitamin D is bound to chylomicrons and transported by the lymphatic system, but it can also be bound to vitamin D transport protein (the α-globulin portion) for transport in the plasma. Some are bound to beta-lipoprotein, and oral vitamin D is bound to chylomicrons and is easier to break down than protein-bound ones from the skin. When vitamin D is transported to the liver, it is hydroxylated at the 25 position to form 25(OH)D (25-hydroxy vitamin D3) by the monooxygenase system in the microsomes. Other tissues outside the liver can also absorb vitamin D and 25-(OH)D3. Therefore, the vitamin D and 25(OH)D3 in the tissues and their total amount are more than in the plasma. If the target tissue needs it, they can be released. They are most abundant in adipose tissue and are released the slowest. They can also be released when weight is lost and fat is reduced. When vitamin D is injected intravenously, it enters the tissues more quickly from the plasma. 25(OH)D3 in plasma reaches its peak 1 to 3 days after injection, and its concentration can reach 20 to 40 ng·ml-1, and up to 80 ng·ml-1.