Vitamin D cycle and calcium control

Vitamin D

Vitamin D is the vitamin known as the sun’s vitamin, as the main source of obtaining it is the body’s exposure to sunlight until the body produces this vitamin, through the skin’s exposure to ultraviolet rays from the sun’s rays, and it converts the cholesterol in the skin through a series of vital processes into Vitamin D. Exposing the hands and feet to the sun from five to ten minutes, two to three times a week is sufficient time to provide the body with its need of vitamin D, in addition to its availability in limited quantities in some foods.

Vitamin D and calcium

Vitamin D increases the level of calcium in the blood by:

  • Increased absorption of calcium from the intestine.
  • Reducing urinary calcium loss by increasing calcium reabsorption in the kidneys.
Here it should be noted quickly that calcium deficiency 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. When the calcium level in the blood increases, the calcitonin (which is produced by Calcitonin) is produced by Thyroid gland to reduce calcium in the blood by increasing its deposit in the bones.

Vitamin D cycle in the human body

  • Vitamin D is one of the fat-soluble vitamins, so the intestine absorbs it with other fats when obtained from food. The vitamin then travels inside the cells transporting through the bloodstream to the liver.
  • Vitamin D is also made in the skin through direct exposure to the sun, as follows:
  1. In the skin there is a substance called 7-dehydrocholesterol.
  2. When the skin is exposed to ultraviolet radiation, the substance (7-dehydrocholesterol) is converted to cholecalciferol (English: Cholecalciferol).
  3. Then the substance (cholecalciferol) travels through the bloodstream until it reaches the liver. 
  4. The liver contains an enzyme (25-alpha hydroxylase), which stimulates the process of converting (cholecalciferol) into (25-hydroxycholecalciferol) (English: 25-hydroxycholecalciferol).
  5. The substance (25-hydroxy cholecalciferol) is transferred to the kidneys.
  6. The kidneys contain an enzyme (1-alpha hydroxylase), which stimulates the process of converting (25-hydroxy cholecalciferol) into a substance (1,25-dehydroxy cholecalciferol) which is called (Vitamin D3) or calcitriol (English: Calcitriol).

The importance of Vitamin D.

What is metabolized in the body is called 1,25-dehydroxy cholecalciferol (English: 1,25 (OH) 2D3)), where vitamin D is involved in many vital processes, including:

  • Maintaining healthy bone growth and development.
  • Maintaining the balance of calcium and phosphorous mineral in the body.
  • Inhibiting the growth of cancer cells.
  • Protecting the body from various immune diseases.
  • Reducing the occurrence of infections in the body.
  • It enters the processes of growth, division and differentiation of different body cells.

The body needs vitamin D.

The reference dietary amount (approved in English: Recommended Dietary Allowances) approved for Vitamin D is the amount sufficient to maintain healthy bones, teeth, and metabolism of calcium in healthy people. This amount varies with the age of the human being as follows:

  • Infants from 0-12 months need 400 IU.
  • Children from one year to 60 years old need 600 IU

Sources of vitamin D.

There are very few foods that contain in nature vitamin D, and the meat of fatty fish (such as salmon, tuna, and mackerel) and fish liver oils are among the best sources, and small amounts of vitamin D are found in the (liver, cheese) , And egg yolks), and it is possible to get vitamin D from fortified foods such as (milk products, butter, and orange juice) provided that it is written in the nutritional information of these foods that they are fortified with vitamin D. Vitamin D can be obtained from support, but should not be taken without consulting a physician. As for exposure to sunlight, most people get a small amount of their vitamin D needs through exposure to the sun, for many reasons, including:

  • Clothing, as clothing can cover a large part of the body when exposed to direct sunlight.
  • Use sunscreen.

Vitamin D deficiency

Vitamin D deficiency appears as rickets in children and osteomalacia in adults, and may lead to osteoporosis and fractures. Vitamin D deficiency is closely related to high incidence of cancer, autoimmune diseases, hypertension and infectious diseases. Not consuming sufficient quantities of vitamin D is widespread around the world regardless of age and health status. Vitamin D deficiency is also linked to a deficiency in absorption and metabolism of calcium.

Vitamin D deficiency and the risk of cancer: The low level of vitamin D in the body is closely related to the risk of cancer and death rate, because vitamin D performs many processes that may slow or prevent the occurrence of cancer, and these processes include:

  • Reducing the growth of cancer cells.
  • Stimulating apoptosis, a natural process that occurs in the cells of the body to maintain the integrity of the body and the vital processes that take place inside it.
  • Promoting the process of cellular differentiation of cells inside the body, which is the process of differentiating cells into different types of specialized cells.
  • Reducing the incidence of angiogenesis of cancer cells, and this process by which cancer cells begin to circulate, through the release of food and energy to the cancer cells through the blood vessels.


  1. L. Kathleen Mahan, Sylvia Escott-Stump, Janice L. Raymond (2014), Food and the Nutrition Care Process, saint louis, united states: saunders elsevier, Page 61-62, 67-69, Part chapter 3, intake:The Nutrients and Their Metabolism. Edited.
  2. Sylvia Christakos, Dare V. Ajibade, Puneet Dhawan, Adam J. Fechner, and Leila J. Mady (2011), "Vitamin D: Metabolism"، PMC, Retrieved 14-9-017. Edited.
  3. "Vitamin D", National Institutes of Health,2016، Retrieved 14-9-2017. Edited.
  4. "Vitamin D and Cancer Prevention", National Cancer Institutes,2013-11-21، Retrieved 2017-9-26. Edited.
  5. Susan Elmore (6-12-2007), "Apoptosis: A Review of Programmed Cell Death"،, Retrieved 18-10-2017. Edited.
  6. "Angiogenesis",, Retrieved 18-10-2017. Edited.

Vitamin D cycle and calcium control