Home 
First 
Prev 
Next Vitamin D is a fat-soluble compound essential for calcium metabolism in animals and normal mineralization of bone and cartilage. The skin forms vitamin D when exposed to sunlight, but in some circumstances sunlight may lack sufficient amounts of ultraviolet rays to bring about adequate production of the vitamin. Technically the molecular species classified as vitamin D is not really a vitamin because it can be produced in the human body. However, for nutritional and public health reasons, vitamin D continues to be classified officially as a vitamin.
Vitamin D is needed for the absorption of calcium and the regulation of calcium levels in the blood. The absence of vitamin D in the food of young animals leads to the development of rickets unless the animal is exposed to sunlight or u.v. irradiation. It is essential for the normal development of teeth, and is used for treating osteomalacia and dental caries.
The vitamin D requirement for healthy adults has never been precisely defined. Since vitamin D is produced in the skin after exposure to sunlight, the human does not have a requirement for vitamin D when sufficient sunlight is available. However, vitamin D does become an important factor of healthy nutrition in the absence of sunlight. It is known that a substantial proportion of the U.S. population is exposed to quite suboptimal levels of sunlight especially during the winter months; it is likely that during these intervals regular dietary supplements of vitamin D should be provided. You can find large selection of high quality and low priced supplemental vitamins HERE and HERE.
In addition to geographical and seasonal factors, ultraviolet light from the sun may also be blocked by air pollution. The tendency to wear clothes, to live in cities where tall buildings block adequate sunlight from reaching the ground, to live indoors, to use synthetic sunscreens that block ultraviolet rays, and to live in geographical regions of the world that do not receive adequate sunlight, all contribute to the inability of the skin to biosynthesize sufficient amounts of vitamin D. Under these conditions vitamin D becomes a true vitamin in that it must be supplied in the diet on a regular basis.
Deficiencies cause many biochemical and physiological imbalances. If uncorrected, faulty mineralization of bones and teeth causes rickets in growing children and osteomalacia (progressive loss of calcium and phosphorus from the bones) in adults. Common early symptoms of rickets include restlessness, profuse sweating, lack of muscle tone in the limbs and abdomen, and delay in learning to sit, crawl, and walk. Rickets may produce such conditions as bowlegs and knock-knees. Deficiency may also cause osteoporosis, a bone condition characterized by an increased tendency of the bones to fracture. Large doses of vitamin D are toxic, and symptoms include weakness, loss of appetite, nausea, vomiting, diarrhea, excessive thirst, and weight loss.
The current Recommended Dietary Allowance (RDA) of vitamin D is 200 IU/day (5 micrograms/day) up to the age of 50. The recommended intake for people from age 51 to 70 is 400 IU/day (10 micrograms), and over age 70 is 600 IU/day (15 micrograms). The RDA of vitamin D for both pregnant and lactating women is recommended to be 200 IU (5 micrograms/day).
In the United States, adequate amounts of vitamin D can readily be obtained from the diet and from casual exposure to sunlight. However, in some parts of the world where food is not routinely fortified and sunlight is often limited during some periods of the year, obtaining adequate amounts of vitamin D becomes more of a problem. As a result, the incidence of rickets in these countries is higher than in the United States.
Animal products constitute the bulk source of vitamin D that occurs naturally in unfortified foods. Salt water fish such as herring, salmon, sardines, and fish liver oils are good sources of vitamin D. Small quantities of vitamin D are also derived from eggs, veal, beef, butter, and vegetable oils while plants, fruits, and nuts are extremely poor sources of vitamin D. In the United States, artificial fortification of foods such as milk (both fresh and evaporated), margarine and butter, cereals, and chocolate mixes help in meeting the RDA recommendations.
