We all talk about how important vitamins and minerals are for health. But if we knew more about why they are so important, we would be more likely to eat the foods that contain these vital vitamins and minerals. To start, I have chosen to explain the why of vitamin D.
Part 1: The Science Behind Vitamin D
Vitamin D is a fat-soluble vitamin (binds with fat in the body to be absorbed) that has an inactive form under the skin. When sunlight hits the skin, it actually activates this vitamin so it can do its various functions in the body. Vitamin D can also be found in its active form in some foods such as fatty fish, milk, and eggs, but it is in small quantities. This really makes you see that sunlight is necessary to maintain adequate vitamin D in the body. Moreover, vitamin D is stored in the body. So, when winter comes around and there is minimal sunlight, most of our bodies rely on the vitamin D stored in fat. If you find that you are not receiving adequate exposure to sunlight or a blood test reveals you are vitamin D deficient, it would be wise to take a vitamin D supplement to ensure you get adequate amounts of it.
Vitamin D’s main job in the body is to maintain adequate calcium levels in the body. For example, when calcium levels are low, the kidneys increase the production of vitamin D, so that vitamin D can then travel to the small intestine to increase intestinal absorption of calcium.
However, vitamin D is now found to have other important functions (besides maintaining calcium balance) as well. It has been discovered that other organs and tissues in the body possess vitamin D receptors (structures on the surface of a cell that selectively receive and bind a specific substance), such as lungs, colon, prostate, and breast. Bone and epidermal (skin) cells also have vitamin D receptors. This is important because vitamin D actually functions as a hormone (a hormone is a compound that exerts a biological response when it binds to its target tissue). So, when vitamin D binds with its receptor it causes a biological reaction in the tissue.
Furthermore, vitamin D is responsible for causing a very important biological reaction called antiproliferation. That is, it acts to decrease cell growth and cell division, which makes vitamin D an important anti-cancer agent. Vitamin D has been found to be an antiproliferative agent for cultured tumor cells (a tumor is an abnormal lump or growth of cells) such as tumor breast, colon, lung, prostate, and melanoma cells that possessed a vitamin D receptor.
Another type of cell with a vitamin D receptor is a promyeloid leukemic cell (a type of white blood cell that functions in the immune system). An interesting finding was that when vitamin D binded to its receptor in these leukemic cells, the biological reaction caused the leukemic cells to become macrophages (a type of white blood cell that works with the immune system to rid the body of toxic substances). The macrophages engulf various toxins and foreign substances in the body that are then to be excreted.
Vitamin D has also been linked to certain skin conditions such as psoriasis. Psoriasis is a hyperproliferative (an abnormally high rate of cell growth and cell division) skin disorder and the anti-proliferative action of vitamin D is now being recognized as a safe and effective treatment for psoriasis.
Part 2 of this series will be: The recommendations for getting adequate vitamin D
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Eisman JA. 1,25-Dihydroxyvitamin D3 receptor and the role of 1,25-Dihydroxyvitamin D3 in human cancer cells in vitamin D. In: Kumar R, ed. Vitamin D. Basic and Clinical Concepts. Boston: Martinus Nijhoff, 1984.