Vitamin D is a very important vitamin and hormone that has several functions in the body, including promoting bone health and cell growth. Before it can be utilized by the body, vitamin D obtained from diet and sunlight must undergo two hydroxylations in the body. The first converts vitamin D to 25-hydroxyvitamin D, also know as calcidiol. This occurs in the liver. The second hydroxylation converts calcidiol to the active form of vitamin D, 1,25-dihydroxyvitamin D. Serum concentrations of vitamin D 25-hydroxy are the best indication for vitamin D deficiency.
Vitamin D
Vitamin D has several functions in the body, such as its role in bone growth, cell growth and promoting calcium absorption in the gut. Adequate vitamin D intake can help prevent rickets in children and osteoporosis in adults. For individuals between 14 to 70 years of age, the recommended dietary allowance for vitamin D is 15mcg per day. Adults who are 70 years of age or older have a recommended dietary allowance of 20mcg per day.
Sources of Vitamin D
There are very few foods that naturally have vitamin D in them; however, foods such as milk, yogurt, cheese, some cereals and orange juice are fortified with vitamin D. Foods with vitamin D in them naturally include fatty fish such as salmon and tuna and fish liver oils. In addition to dietary sources, vitamin D can also be synthesized when the skin is exposed to sunlight.
Deficiency Symptoms
Symptoms of a vitamin D deficiency include fatigue, weight loss, osteoporosis and rickets. Osteoporosis is very common among the elderly and is classified by brittle, thin bones. Rickets is a disease in children that results in bone tissue failing to properly mineralize, resulting in soft bones and other skeletal deformities.
High-Risk Groups
Individuals who are at higher risk for a vitamin D deficiency include older adults, individuals who have limited sun exposure or fat malabsorption and individuals who have had gastric bypass surgery. Older adults are at risk because skin becomes less efficient at synthesizing vitamin D with aging. In addition, more time is spent indoors and intake of vitamin D is usually inadequate. Individuals with limited sun exposure are unable to get adequate vitamin D from sunlight and if dietary intake is inadequate, a deficiency can occur. Vitamin D requires fat to be absorbed, so individuals with fat malabsorption also may have a deficiency in vitamin D. In individuals who have undergone gastric bypass surgery, the small intestine, where vitamin D is absorbed, is bypassed. Supplements may be beneficial if dietary intake is inadequate.
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