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Facts About Vitamin D Vitamin D, also known as calciferol, is popularly referred to as the "sunshine vitamin." Vitamin D can be synthesized in the body with appropriate exposure to the ultra-violet rays of the sun (a process called photosynthesis). This process requires cholesterol, so the resulting fat-soluble vitamin form is known as "cholecalciferol." The synthesized vitamin enters the bloodstream and makes its way to the liver, where it is converted to 25-hydroxycholecalciferol. From there, it goes to the kidneys for the final conversion to 1,25 dihydroxycholecaciferol.1 In this final form, as a natural hormone, the body uses vitamin D to help calcium absorption in the intestines, and to release calcium stores from the bones when necessary to maintain calcium blood levels.1 Within the small intestine, vitamin D helps calcium to be absorbed, rather than excreted, by activating a process in the mucous membranes that actively transports calcium to the blood.1,2 It similarly helps the absorption of phosphorus, another bone-building mineral.2 If there is not nough calcium available in the small intestine because of a low calcium diet, vitamin D, with the help of para-thyroid hormone causes the bones to release necessary amounts of calcium and phosphorus into the blood stream.3 This stabilizing process on blood calcium and phosphorus levels helps to maintain many body functions. If blood calcium is not kept stable, disturbances of nerve function can result in muscle twitching and spasms.2 Recent research has revealed additional roles for vitamin D. The immune system is sensitive to vitamin D levels and may not function normally if vitamin D is insufficient.*4,5 Vitamin D may also help prevent abnormal cell growth.*6 Supplements of vitamin D come in two forms: D-2 and D-3. Ergocalciferol (D-2) is commercially produced from ergosterol found in plants or yeast. The more abundant natural vitamin D-3 is traditionally concentrated from fish liver oils. No matter where vitamin D comes from, it is a result of sunlight and photosynthesis by plants and animals. Vitamin D Deficiency Typical diets normally contain less than RDA levels of Vitamin D. Regular fish consumption may meet requirements, as well as consistent intake of vitamin D-fortified products, such as milk. Vitamin D deficiency is common, however: people that may become deficient in vitamin D include those that live in polluted or cloudy environments, wear long, dark clothing, or have high levels of pigment in their skin – in essence, limiting their exposure to the sun.3,7 People with liver, kidney, pancreas, or intestinal disorders may also suffer from a deficiency.*3 Seniors may have some trouble maintaining vitamin D levels since most do not spend as much time in the sun, and their bodies’ ability to make and use vitamin D is less efficient.8,9,10,11,12,1,14 Geographic location is a determining factor in vitamin D deficiency: the further away from the equator, the less sunlight is available. In one study of 23 elderly people, levels of vitamin D were normal in July, but fell by up to 65% the following February.15 Other studies support these findings.16,17 Low vitamin D levels can result in brittle bones in the elderly,18,19 and most research has shown that vitamin D supplements help elderly people maintain healthy bone density.*20,21,22 Pregnancy, childhood and menopause increase the need for vitamin D. In two studies that monitored infants fed exclusively with breast milk, it was found that supplementation with vitamin D, calcium and phosphorus was necessary to prevent rickets.23,24 A lack of sunlight and the presence of skin pigment were also determining factors. In the 1920s, scientists started to correlate the absence of vitamin D with the bone disease rickets. In children, a lack of vitamin D causes the bones to be soft since the matrix of calcium and phosphorus does not form properly. In turn, this affects joints and muscles. Children with rickets have bowed legs, since their legs cannot support the weight of their body. They may also have a "barrel" chest due to an enlarged liver. In adults, a deficiency in vitamin D causes osteomalacia – (soft bones) from low calcium absorption and increased release of calcium from bones in order to maintain stable blood levels. Cell differentiation is the process by which cells specialize to perform specific functions in different tissues. Loss of cell differentiation can lead to abnormal cell function, including uncontrolled cell growth. Two recent reports discuss several studies that show that the presence of vitamin D improves cell differentiation and reduces the risk of abnormal cell growth.*25,26 Safety of Vitamin D The Recommended Dietary Allowance is 400 IU for most age groups, including pregnant and lactating women. It is important to note that complementary levels of calcium and phosphorus should also be maintained.2 One study reports that adult levels up to 10,000 IU/day offer "no evidence of adverse effects."27 According to another source, however, very young children develop symptoms of hypervitaminosis D with as little as 1,800 IU/day.28 Due to its action of releasing calcium from storage in bones, excess vitamin D over periods of time may cause elevated blood levels of calcium, which is then deposited in soft tissue. Eventually, this can lead to formation of kidney stones, as well as calcium deposits in arteries and other body parts. 3 Symptoms of vitamin D excess may include weakness, disorientation, nausea and constipation.3 People with hyperparathyroidism or sarcoidosis (a lymph disorder) should not use vitamin D supplements except under medical supervision. References
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