Vitamin D is a common term for a related group of nutrients that you can consume in food or supplements, or create internally by exposing your skin to sunlight. Some people develop vitamin D deficiencies that significantly alter their health. There are a number of possible dietary and non-dietary causes for these deficiencies.
Basics
Relatively few foods naturally contain vitamin D, according to the National Institutes of Health's Office of Dietary Supplements. Readily available sources of the vitamin include fatty fish such as tuna and salmon, fish liver oil, cheese, egg yolks and beef liver. These foods contain a form of the vitamin called D3, or cholecalciferol. Some species of mushrooms contain another form of the vitamin, D2, or ergocalciferol. When your skin is exposed to direct sunlight, you make vitamin D3 internally. Foods fortified with vitamin D --- including milk, cereal and juice --- provide the main source of the nutrient for most Americans. These products can contain D2 or D3.
Sources of Deficiency
When you obtain vitamin D from any source, your body must put it through a two-stage conversion process to make it biologically active and useful. You can develop a deficiency if any part of this process breaks down. You also can develop a low vitamin D status if your diet doesn't contain enough of the nutrient, or if your body lacks the ability to properly absorb the vitamin from the foods you eat. In addition, you can develop a deficiency if your vitamin D requirements increase or if your body eliminates too much of the vitamin from your system.
At-Risk Populations
Certain people have a heightened risk for develop a vitamin D deficiency. People with dietary risks include vegans and ovo-vegetarians, as well as people with milk allergies and those who avoid dairy products as a result of lactose intolerance. Other groups at risk include breastfed babies, who typically can't enough of the vitamin from human milk; people with dark skin, who might not absorb enough sunlight to maintain vitamin D levels; people who can't absorb the fat needed to support vitamin D processing; people with restricted sun exposure; people who have received a gastric bypass or are obese; and older people, who might have low vitamin intake or reduced vitamin D processing efficiency.
Considerations
Males and females between the ages of 1 and 70 need 600 IU of vitamin D a day for optimum health, according to the National Academy of Sciences' Institute of Medicine, which sets official nutrient intake standards. Males and females over 70 need 800 IU, while pregnant and lactating women and teens need 600 IU. Infants need at least 400 IU per day. Significant health problems associated with low vitamin D in adults include a bone disorder called osteomalacia and a parathyroid gland disorder called secondary hyperparathyroidism. Infants and children with severe vitamin D deficiencies can develop a bone disease called rickets.
If you have concerns about your vitamin D levels, consult your doctor for additional information and advice.
References
- MayoClinic.com: Vitamin D; Background
- Office of Dietary Supplements - National Institutes of Health: Dietary Supplement Fact Sheet; Vitamin D
- Oregon State University - Linus Pauling Institute; Vitamin D; Jane Higdon, Ph.D.; March 2004
- Institute of Medicine of the National Academies; DRIs for Calcium and Vitamin D; November 30, 2010
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