Home / Vitamins And Deficiencies / Vitamin D
Vitamin D is produced in the body in the presence of sunlight. Because it is fat soluble it is stored in the body.
Calciferol is encountered in the primary form known as cholecalciferol (D3) and also as ergocalciferol (D2).
Sun exposure is perhaps the most important source of vitamin D because exposure to sunlight provides most humans with their vitamin D requirement. Ultraviolet (UV) rays from the sun trigger vitamin D synthesis in skin. The seasons, geographic latitude, time of day, cloud cover, smog, and sunscreen affect UV ray exposure and vitamin D synthesis.
For example, sunlight exposure from November through February in Boston is insufficient to produce significant vitamin D synthesis in the skin. Complete cloud cover halves the energy of UV rays, and shade reduces it by 60%. Industrial pollution, which increases shade, also decreases sun exposure and may contribute to the development of rickets in children with insufficient dietary intake of vitamin D.
It is important for individuals with limited sun exposure to include good sources of vitamin D in their diet.
Vitamin D is involved in:
In the absence of vitamin D, dietary calcium is not absorbed efficiently. Vitamin D stimulates a number of proteins involved in transporting calcium from the lumen of the intestine, across the epithelial cells and into blood. The best-studied of these calcium transporters is calbindin, an intracellular protein that ferries calcium across the intestinal epithelial cell.
Vitamin D receptors are present in most if not all cells in the body and vitamin D has a potent effects on the growth and differentiation of many types of cells. This suggests that vitamin D has physiologic effects much broader than a role in mineral homeostasis and bone formation. There is research being conducted on the functions of vitamin D and more information about its functions will be available in the near future.
The classical manifestation of vitamin D deficiency is rickets, which is seen in children and results in bony deformities including bowed long bones. Deficiency in adults leads to the disease osteomalacia. Both rickets and osteomalacia reflect impaired mineralization of newly synthesized bone matrix, and usually result from a combination of inadequate exposure to sunlight and decreased dietary intake of vitamin D.
Vitamin D deficiencies are also associated with tooth decay and osteoporosis.
Vitamin D deficiency or insufficiency occurs in several other situations. These include:
Vitamin D is contained in fish (such as mackerel and herring), egg yolks and fish liver oils and some fortified foods.
The absorption of vitamin D supplements will be encouraged by taking the supplements at the same time as eating a meal which contains some fat.
Most capsules contain approximately 400 IU (in the form of natural fish liver oil) and doses between 400 and 1,000 IU can be taken daily. Dosages above 1,000 IU are not recommended.
The elderly are less able to efficiently synthesize vitamin D and may require vitamin D supplements.
Vegans, especially those who live in cold climates are advised to take vitamin D supplements.
Vitamin D is fat soluble and large or repeated doses can build up to toxic levels in the body. The symptoms of toxicity include:
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