Vitamin D is the vitamin known as the sun’s vitamin. The main source of vitamin D is the sun’s exposure to the sun until the body produces it. By exposing the skin to ultraviolet light from the sun, it converts the cholesterol in the skin through a series of vital processes into Vitamin D. Exposing the hands and feet to the sun for five to ten minutes, two to three times a week is long enough to provide the body with its vitamin D requirement, as well as having limited amounts in certain foods.
Vitamin D and calcium
Vitamin D increases the calcium level in the blood by:  Increasing calcium absorption from the intestines. Reduce calcium loss through urine by increasing calcium reabsorption in the kidneys. Here, it should be noted quickly that lack of calcium in the blood stimulates the secretion of parathyroid glands of the hormone, which works to increase the level of calcium in the blood by analyzing calcium from the bones, and when calcium in the blood increases, calcitonin hormone produced by English The thyroid gland reduces blood calcium by increasing its sedimentation in the bones
.Vitamin D cycle in the human body
Vitamin D is one of the fat-soluble vitamins, so it is absorbed by the intestine with other fats when obtained from food, and the vitamin is then transported into the cells that carry the bloodstream to the liver.   There is a substance called 7-Dehydrocholesterol in the skin. When the skin is exposed to ultraviolet light, the substance (7-dihydrocholesterol) turns into cholecalciferol. Cholecalciferol then travels through the bloodstream until it reaches the liver. The liver contains an enzyme (25-alpha hydroxylase), which stimulates the process of converting (cholecalciferol) to (25-hydroxy cholecalciferol) (in English: 25-hydroxycholecalciferol). 25-hydroxy cholecalciferol is transferred to the kidneys. The kidneys contain an enzyme (1-alpha hydroxylase), which catalyzes the process of converting 25-hydroxy cholecalciferol into 1,225-dihydroxy cholecalciferol, which is called vitamin D3 or calcitriol.
The importance of vitamin D
.Vitamin D, which is metabolized in the body, is called 1.25-dihydroxy cholecalciferol (1,25 (OH) 2D3). Vitamin D is involved in many vital processes, including: Maintain healthy bones and teeth. Maintain the mineral balance of calcium and phosphorus in the body. Inhibiting the growth of cancer cells. Protect the body from various immune diseases. Minimize the occurrence of infections in the body. Involved in the processes of growth, division and differentiation of different body cells. 
The body needs vitamin D.
Recommended Dietary Allowances for Vitamin D are adequate for maintaining healthy bones, teeth, and calcium metabolism in healthy people.  Infants age 0-12 They need 400 IU. Children from 1 to 60 years require 600
Sources of vitamin D.
There are very few foods that contain vitamin D in nature, and the meat of fatty fish (such as salmon, tuna, mackerel), liver fish oils from the best sources, and there are small amounts of vitamin D in (liver, cheese Vitamin D can be obtained from fortified foods such as milk, butter, and orange juice, provided that the nutritional information of these foods is supported by vitamin D. Vitamin D can be obtained from supplements, but should not be taken without consulting a doctor. For sun exposure, most people get a small amount of their vitamin D needs through exposure to the sun, for many reasons, including:  Clothes; clothing can cover a large part of the body when exposed to direct sunlight. Use sunscreen.