Vitamin D is a fat-soluble vitamin. It helps the body absorb calcium and plays a crucial role in the growth and maintenance of strong, healthy bones. In children, getting enough vitamin D is important for the prevention of rickets. And in adults, vitamin D deficiency has been associated with a greater incidence of hip fracture. Increased intakes of vitamin D, on the other hand, have been associated with less bone loss in older women. This has led some researchers to believe that vitamin D supplementation may help prevent fractures resulting from osteoporosis.
Recent research suggests that vitamin D may play a role in a number of other conditions, as well. More research is needed to confirm the findings, however. For example, vitamin D deficiency has been related to muscle weakness and pain. In one study, patients with low back pain received high doses of vitamin D for three months, which resulted in significant improvement of their symptoms.
Also, there is some research to suggest that this supplement may play a role in cancer prevention. Vitamin D receptors have been found in breast and prostate tissue, implying that such a link does exist. Additionally, there is some evidence hinting that low levels may play a role in the development of high blood pressure. There is also preliminary research suggesting that long-term vitamin D supplementation decreases the risk ofmultiple sclerosis.
People who are at high risk for vitamin D deficiencies are the elderly, those who get minimal sun exposure or those who use sunscreen whenever they're outdoors. Also, people with conditions that may impact intestinal absorption, such as Crohn's disease, are at risk.
In addition, infants that are breastfed only may require additional supplementation with vitamin D starting within the first days of life. Requirements for pregnant women are the same as for healthy adults. Some believe that pregnant mothers should take more vitamin D than recommended. However, since there is an increased risk of vitamin D toxicity with increased intake, such recommendations need to be discussed individually with a doctor.
The recommended intakes for vitamin D are:
Vitamin D is found in some foods, but the main sources are fortified milk and sunlight. The ultraviolet rays of the sun react with cholesterol present on the skin and create previtamin D3. This compound goes through a series of reactions involving the kidneys and the liver, and the final product is vitamin D.
Most people's bodies can make enough vitamin D with 10-15 minutes of sun exposure 2-3 times per week. However, this synthesis is affected by age, season, latitude, time of day, cloud cover, smog, and skin pigmentation.
Other food sources of vitamin D include:
International Food Information Councilhttp://www.ific.org/
National Coffee Association of USAhttp://www.ncausa.org/
Canada's Food Guidehttp://www.hc-sc.gc.ca/
Dietitians of Canadahttp://www.dietitians.ca/
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Vitamin D. Office of Dietary Supplements, National Institutes of Health website. Available at: http://ods.od.nih.gov/factsheets/vitamind-quickfacts/. Accessed April 14, 2011.
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Last reviewed April 2011 by Brian Randall, MD
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