There are two forms of Vitamin D, one made by plants (ergocalciferol or Vitamin D2) and one made by animals (cholecalciferol or Vitamin D3). Both forms of Vitamin D can be synthesized from sunlight.
Though it is considered a vitamin, Vitamin D actually acts much like a hormone by attaching to DNA receptors to promote cell differentiation. Vitamin D is most active in the intestine, kidneys, and bones.
One of the most important roles of Vitamin D in the human body is to boost the absorption of calcium into bone. In addition to being vital to bone development and strength, Vitamin D is also an important partner in many other processes that require calcium.
Vitamin D also helps to keep teeth and gums healthy, especially in older adults. Studies show that inflammatory gum disease occurs much less frequently in people older than 50 who have adequate Vitamin D intake.
Two signs that Vitamin D may not be present in the body in adequate amounts are poor bone development in children (a condition known as rickets) and softening of the bone (osteomalacia) in adults. Bone pain and fractures may also indicate a need for more Vitamin D. In addition, since Vitamin D is involved in cell growth and differentiation, it may play a role in preventing certain cancers.
Recommended daily amounts of Vitamin D are 5 micrograms (200 I.U.) for children, 5-10 micrograms (200-400 I.U.) for adults up to age 70, and 15 (600 I.U.) micrograms for adults 70 and older. In most cases, Vitamin D requirements can be met with adequate sun exposure.
However, some people, such as those who are home-bound or live in cool climates where skin is usually covered or those who wear sunscreen all of the time may need to obtain Vitamin D from foods.
Foods that are naturally good sources of Vitamin D include cod, snapper, shrimp, halibut, and eggs. Because it is so important to skeletal development, milk and other foods are often fortified with Vitamin D.
Vitamin D is also available in supplements, usually as part of a calcium or multivitamin formula. Vitamin D should not be taken in supplemental doses of more than 100 micrograms (2000 I.U.).
Too much Vitamin D can raise levels of blood calcium above normal limits and put one at risk for developing kidney stones. Excess calcium can also cause blood vessels to constrict, possibly resulting in high blood pressure. In addition, Vitamin D toxicity may cause headaches, nausea, vomiting, fatigue, irritability, or loss of appetite.
Certain health conditions may affect a person’s ability to absorb and utilize Vitamin D. Since it is a fat-soluble nutrient, people on low fat diets and those who are unable to absorb fat due to digestive disorders may not absorb adequate amounts of Vitamin D.
Also, parathyroid, kidney, or liver disease may compromise the conversion of Vitamin D precursors into the active form of Vitamin D. Also, since fewer Vitamin D precursors are produced in the skin as people age, older people may be at greater risk for Vitamin D deficiency.
Certain medications, such as anticonvulsants, bile acid sequestrants, stomach medications, hormones, corticosteroids, and anticoagulants, can interfere with the body’s ability to absorb Vitamin D, while Vitamin D can interfere with calcium channel-blockers. While Vitamin D encourages the release of calcium into the blood, calcium channel blockers discourage this release.
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