Vitamin D is a fat-soluble vitamin. The foods that are sources of vitamin D include fish, fish oil, egg yolks, cheese and beef liver. Breakfast cereals are often fortified with vitamin D. Also, all milk produced in the United States is fortified with vitamin D. Vitamin D is also produced by skin when exposed to sunlight. Despite these sources of vitamin D, cases of vitamin D deficiency occur. Understanding the consequences of a deficiency in vitamin D can lead to a better understanding of the importance of ensuring the body's requirements for vitamin D are met.
Nutritional Role
Vitamin D is needed for calcium absorption in the body. It helps the body to control the amounts of calcium and phosphates. The National Library of Medicine states that in cases of vitamin D deficiencies, hormones will be produced that result in calcium and phosphate being released from bones, resulting in bones that are softened and weakened. The National Institutes of Health reports that rickets and osteomalacia are the diseases that are typically associated with deficiency in vitamin D. Rickets occurs in children, causing skeletal abnormalities and soft bones due to improper mineralization of the bones. Osteomalcia is a condition that is associated with weakened muscles as well as weakened bones.
Reasons for Deficiency
The National Institutes of Health lists four reasons why deficiencies of vitamin D occur. A deficiency can occur when the dietary intake of vitamin D is less than needed; when there is limited exposure to sunlight; when kidneys cannot convert vitamin D into the needed active form; and when absorption of vitamin D from the digestive tract is insufficient.
At Risk
The people who are at risk for vitamin D deficiencies include people who are lactose intolerant because they may be unable to digest sufficient milk that has been fortified with vitamin D. People who are allergic to milk are also at risk for vitamin D deficiency. Strict vegetarianism also puts people at risk for vitamin D deficiency. Other groups have been identified as susceptible to vitamin D deficiencies. Infants who are breastfed require vitamin D because breast milk does not provide sufficient vitamin D for the infant. Americans who are 50 and older have higher vitamin D needs because the skin, as it ages, loses its ability to produce vitamin D when exposed to sunlight. Dark skin reduces the skin's ability to produce vitamin D, and so people with dark skin are at higher risk. Obesity also increases the risk of vitamin D deficiency because the increased mass of fat sequesters vitamin D and changes the amounts released into circulation.
Adequate Intake
The Adequate Intake (AI) for vitamin D as established by the Office of Dietary Supplements is broken down by age. For people aged 50 and below, 5 mcg is the recommended daily dose. This is the same as 200 International Units (IU). For people aged 51 to 70, the AI is 400 IU, or 10 mcg. For people older than 70, 600 IU, or 15 mcg, is recommended.
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