Vitamin D, an essential pro-hormone, can be found in the diet and synthesized in the body from sunlight. According to the National Institute of Health, it has many important functions including bone formation and maintenance, immune system functions, calcium absorption, insulin production and inhibiting parathyroid hormone secretion. Dietary forms of vitamin D include salt water fish, fish liver oils and fortified milk and dairy products high in calcium. Deficiency is rare in developed countries, especially if foods are fortified, however it can cause serious problems such as hypocalcemia, rickets and osteomalacia.
Low Intake
Low intake of vitamin D over time can develop into a deficiency. The National Institute of Health states the adequate intake, which represents a daily intake sufficient enough to maintain bone health and normal calcium metabolism in healthy people, is 5 micrograms for men and women up to age 50. After age 50 the AI increases to 10 mcg, and after 71 years the AI increases to 15 mcg. As previously stated, most countries fortify foods high in calcium with vitamin D. Other sources include fortified fruit juices and drinks, breakfast cereals and margarine.
Inadequate Exposure
According to the National Institute of Health, exposure to sunlight will allow most people to reach their vitamin D needs. Recommendations include exposure to face, hands and arms for around five to 15 minutes a day will be adequate. In populations living in areas where sunlight is not always accessible, such as those living at northern latitudes or women who wear long robes and head coverings, vitamin D deficiency can develop.
Reduced Absorption
In those with digestive diseases or absorption issues, dietary vitamin D may not be fully broken down or absorbed in the digestive tract. According to the National Institute of Health, only a small amount of vitamin D is stored in the body so not reaching the daily amount through absorption of dietary sources potentially causes deficiency.
Abnormal Metabolism
The kidneys help produce the active form of vitamin D in the body, according to the Merck Manual. When the kidneys are not working properly, for example in chronic renal disorder, the amount of vitamin D produced decreases. Other problems like hereditary or certain liver disorders can also affect the production of the active form of vitamin D.
Other Causes
Primarily breastfed infants with little to no sunlight exposure are at high risk for developing vitamin D deficiency. According to the National Institute of Health, breast milk only provides 10 percent of an infant's daily needs and a supplement could be warranted in these circumstances. Also, certain dark-skinned populations are usually unable to meet their vitamin D needs with sunlight exposure due to high levels of melanin in the skin.
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