Vitamin D promotes the building of strong, healthy bones by stimulating the absorption of calcium and phosphorus---two minerals necessary for bone growth. Because very few natural food sources provide vitamin D, it can be difficult to maintain the necessary levels. A vitamin D deficiency can occur due to an inadequate intake of vitamin D, impaired absorption of vitamin D in the digestive system and failure of the kidneys to convert vitamin D into its active forms. The prevalence of vitamin D deficiency depends upon the location, the race and the age of the patient.
Food Sources
Vitamin D occurs naturally in cod liver oil, salmon, mushrooms, mackerel, tuna, egg yolk and beef liver. Many more food items are fortified with vitamin D. In fact nearly all the milk produced in the United States contains an added 100 IU of vitamin D per cup, according to the National Institutes of Health Office of Dietary Supplements. Other foods fortified with vitamin D include yogurt, orange juice, margarine and ready to eat cereals.
Vitamin D From the Sun
In addition to getting the recommended amount of vitamin D in food sources, the sun triggers the production of vitamin D in the body. The ultraviolet rays of the sun stimulate the cells in the skin to convert the substance known as previtamin D3 into D3, an active form of vitamin D. As a result, the prevalence of vitamin D deficiency is affected by the season, geographic location, cloud cover, smog and time of day.
Vitamin D Deficiency in the United States
Because the United States fortifies food products, including milk and ready to eat breakfast cereals, with vitamin D, the prevalence of vitamin D deficiency remains lower than other countries, especially less developed countries. Data provided by the National Health and Nutrition Examination Survey in 2005 to 2006 revealed that approximately one-third of all those over the age of one received the necessary amounts of vitamin D through foods, according to the National Institutes of Health Office of Dietary Supplements. The number of food fortified with vitamin D, the use of supplements and access to sun exposure in the U.S. boosts the vitamin D levels and has made severe vitamin D deficiency, which causes rickets in children, a rare disease.
Vitamin D Production in Darker Skin
Skin cells produce a pigment known as melanin. As the content of melanin in the skin increases, the skin's ability to produce vitamin D from sunlight decreases. This means that those with darker skin produce less vitamin D when exposed to the sun. This explains why African Americans have a higher prevalence of vitamin D deficiency across all age groups, according to information provided by Wilkins and Associates in the April 2009 issue of the "Journal of the National Medical Association."
Age
As people age their skin loses the ability to produce vitamin D substances and the kidneys lose their ability to convert them into the active forms of vitamin D, according to the National Institutes of Health Office of Dietary Supplements. This means that those over the age of 50 have an increased risk of developing vitamin D deficiency, making deficiency more prevalent among older patients.
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