Vitamin D is a fat-soluble vitamin that is used by the body for bone growth and remodeling. It works in tandem with calcium to help prevent osteoporosis. Vitamin D is also essential for cell growth, neuromuscular and immune function and reducing inflammation. It is naturally found in very few foods but is added to some, such as milk. Sunlight can also trigger production of vitamin D in your skin.
Blood Levels of Vitamin D
A normal, healthy range of vitamin D is 20-49 ng/mL. This indicates adequate levels for overall bone health in otherwise healthy people. A level from 12-19 ng/mL is considered inadequate and should be corrected by supplementation or increased vitamin D intake. Levels below 12 ng/mL are a deficiency and can cause rickets in infants and children and softening of the bones in adults. Vitamin D levels above 49 are too high and may lead to adverse side effects such as anorexia, weight loss, heart arrhythmias and damage to the kidneys and blood vessels.
Sources of Vitamin D
Some of the best sources of vitamin D are in fatty fish such as tuna, mackerel and salmon. Small amounts can be found in egg yolks, cheese and beef liver. Most Americans get vitamin D from fortified foods. Milk was fortified starting in the 1930s in response to rickets, a major health problem at the time. Some manufacturers of yogurt, cereal, margarine and orange juice fortify their products with vitamin D.
Symptoms of Vitamin D Deficiency
Too little vitamin D can cause rickets, which leads to softening and weakening of the bones. Symptoms include bone pain or tenderness in the spine, pelvis, arms and legs. Dental deformities and cavities may be present. Rickets causes skeletal deformities, impaired growth and increased bone fractures. In addition to low dietary consumption, deficiency of vitamin D can be caused by staying indoors most of the time and not getting enough exposure to sunlight.
Recommended Daily Intake
The U.S. Institute of Medicine of the National Academy of Sciences recommends 200 International Units per day from birth to age 50. The upper limit for children younger than one year is 1,000 IU per day, while the upper limit for children older than one year is 2,000 IU. Some authors question this recommendation, especially for those who do not get regular sun exposure. A 2008 review recommends 400 IU daily for infants and children.
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