Vitamin D serves several important functions in the body. Your bones need it for growth and repair, and it helps the body absorb calcium, which is necessary for bone integrity. Vitamin D is also a vital nutrient for the immune system. The primary source of vitamin D for humans is through exposure to sunlight, but it is also available in some foods and as a supplement. Because it is absorbed in the fat, there is a risk of toxicity if you take too much. Consult a doctor regarding your specific needs.
Vitamin D
Vitamin D is actually not a vitamin, according to the National Cancer Institute; it is a fat-soluble group of substances that are precursors to hormones. The most important of these substances are vitamin D3 -- cholecalciferol -- and vitamin D2 -- ergocalciferol. Vitamin D2 and D3 are transformed in the liver and kidney to the active form of 1,25-dihydroxyvitamin D, or calcitriol, which is what acts on the bones and immune system. You can get vitamin D3 by being exposed to sunlight, but vitamin D2 only comes from a plant source. However, both vitamins can be manufactured. Milk is often fortified with added vitamin D.
Bones
There are several factors that influence bone development and growth including nutrition, physical exercise and secretions of various hormones. All of these processes are directly or indirectly related to Vitamin D production or use. The most important aspect is exposure to sunlight because the skin can transform the ultraviolet rays of the sun into vitamin D3. The vitamin D3 then gets transformed to calcitriol, which helps the body absorb calcium in the small intestine. This is important because if the calcium is not absorbed in the small intestine, the body turns to the bones for needed calcium. The body will continue to take calcium from the bones to keep the calcium levels in the blood at normal levels. Over time, this can create health problems because calcium is vital for bone growth and maintenance.
Deficiency
Children who don't get enough vitamin D can suffer from rickets, which results in weak, soft bones that can easily fracture or grow abnormally. Adults who don't get enough vitamin D can suffer osteomalacia -- a softening of the bones, or osteoporosis, which is actual deterioration of the bones. A deficiency in vitamin D can also result in other issues, such as high blood pressure, heart disease and other medical disorders.
Recommended Intake
People younger than 50 years of age need at least 200 international units a day of vitamin D through diet or supplement use, regardless of how much they get through exposure to the sun, according to the New York State Department of Health. People between 51 and 70 need 400 IU's a day. That number increases to 600 for those older than 71 years of age. The recommended limit of oral intake of vitamin D is 2,000 IUs a day, because it does get absorbed in the body fat and is toxic at higher levels. Most vitamin D comes from casual exposure to sunlight. You can get enough by exposing your hands and feet for five to 10 minutes a day, three days a week. Wear sunscreen when ultraviolet levels are moderate or higher. Fish, fortified milk and eggs are good food sources of vitamin D and, consumed in moderation, can provide adequate amounts of vitamin D when combined with sunlight exposure. Consult a doctor before taking a supplement.
Considerations
Some individuals may need a higher does of vitamin D to help prevent or mediate certain health conditions. Most people get enough vitamin D from sunlight, diet and supplements, but those over a certain age, as well as menopausal women, often need more vitamin D than the recommended amount. People who don't get a lot of exposure to the sun may need a to take more as well. If you have health issues or think you may need more than the recommended amount of vitamin D, consult a doctor.
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