Vitamin D is a member of the fat-soluble vitamins that includes Vitamin A, Vitamin K and Vitamin E. Vitamun D is also known as Calciferol and as the “sunshine” vitamin. The status as a vitamin is ambiguous as skin cells in the presence of sun light (UVB radiation) are capable of synthesizing it from a cholesterol derivative. It is therefore more correctly classified as a prohormone.
The prohormone form whether synthesized in the body or obtained from the diet is converted by enzymes from the liver and kidneys in the active form and delivered to target organs. The vitamin status has been given because it can prevent and to some extent treat the diseases rickets and osteomalacia.
The amount of sun exposure necessary to produce vitamin D depends on age, skin color time of the day and geographic location. Experts recommend 10 to 15 minutes of exposure to hands arms and face, three times a week. Exposure to the sun is effective for the synthesis of vitamin D between the hours of 8am and 4pm. It is not effective at all in northern climates in winter and people may able to use stores in adipose tissue (fat cells) from the summer months. Anyone with insufficient stores must receive it from dietary or supplemental sources. Patients with chronic fat-malabsorption syndromes such as Crohn’s disease, celiac disease and cystic fibrosis have difficulty absorbing vitamin and may develop deficiency.
Vitamin D aids in the absorption of calcium and breakdown and assimilation of phosphorus. Its principal role is to maintain serum calcium and phosphorus concentration. This is necessary for the normal development of bones and teeth in children, proper calcification of bones and in maintaining a stable nervous system, normal blood clotting, heart action and other cellular processes. These functions become possible when sufficient vitamin D is present for the proper utilization of these minerals. The body can store sufficient reserves of the vitamin.
Compared to other vitamins, very few foods contain significant amounts of vitamin D. Fatty fish such as salmon, tuna and mackerel, are among the good sources. It is also found in smaller amounts in liver eggs and cheese. The vitamin D in plant sources is called vitamin D2 or ergosterol whereas from animal origin, is slightly different and called D3. A balanced diet and sufficient sun exposure can provide enough D to meet much of most peoples needs.
Several studies suggest that older people, especially those who live in northern climates and anyone that spends most of the day indoors and ingest little vitamin D are at risk of developing a deficiency. It is thought that up to 50% of such older patients with hip fracture may be deficient. Other studies, mainly supported by in vitro experiments, suggest that sufficient vitamin D can influence cell differentiation in some cancer cells and reduce the risk of developing colon, prostate, breast and bone cancer.
Vitamin D can be very toxic if consumed regularly, 6 to 12 months, and of 5 to 10 times higher than the Adequate Intake. If you are contemplating supplementation you must consider a dose no higher than 400IU/day to 800 IU/day. The set Upper Level is 2000 IU/day. These supplement it is best if used under the guidance of your physician or health care provider due to the health risks that may occur as a result of overdose.
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Vitamin A – Retinol - Carotene | Health and Fitness Hints
on July 1 2008
[...] A is also called retinol is another member of the fat-soluble nutrients such as vitamin D and K that occurs naturally in two different forms; pro-vitamin A or carotene and the preformed [...]