Vitamin D is a fat-soluble vitamin synthesized in skin and then activated in liver and kidneys. It plays a very important role in calcium and phosphorus metabolism. Together with calcium and phosphorus, it is required by the body to maintain strength of bones. Its deficiency causes defective mineralization of bone matrix. Symptoms in children are weakness, bowing of weight-bearing bones and teeth problems. In adults, vitamin D deficiency causes a condition known as osteomalacia.
Causes Of Deficiency
Osteomalacia means soft bones. Vitamin D deficiency is the most common cause of osteomalacia. Up to 25 percent of postmenopausal women have some vitamin D deficiency. Incidence of severe vitamin D deficiency is 3.5 percent in the United States. Vitamin D deficiency may arise from insufficient sun exposure, malnutrition, malabsorption and kidney diseases like renal failure and nephrotic syndrome. Medicines including bile acid biding drugs like cholestyramine and anti-seizure medications like phenytoin can also decrease vitamin D levels. Milk, especially skim milk, is a poor source of vitamin D
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Presentation of Osteomalacia
It is initially asymptomatic. Eventually, bone pain and painful muscle weakness especially in pelvic girdle ensues. These symptoms are due to calcium deficiency. These patients have tendency for easy fractures with little or no trauma. Its signs and symptoms mimic osteoporosis and careful distinction between the two is necessary.
Diagnosis
Alkaline phosphatase is an enzyme released with any damage to bone cells. It may be elevated in serum. The most important diagnostic test is blood level of 25-hydroxy vitamin D3 less then 10 ng/mL. Blood level of calcium or phosphate may be low as well. X-rays show characteristic bone thinning and stress fractures.
Prevention
Vitamin D-fortified food has decreased the incidence of vitamin D deficiency. Sun exposure for few hours per week is beneficial in sun-deprived patients. Daily intake of multivitamin containing 400 IU of vitamin D is enough to prevent its deficiency. Older patients with osteoporosis are benefited by 800 IU of vitamin D with calcium supplementation of 1 to 2 g per day.
Treatment
Severe deficiency leading to osteomalacia can be treated with high dosages initially 50,000 IU per week for 6 to 12 months followed by maintenance therapy of 1,000 IU daily. Oral calcium supplements like calcium citrate provide 0.4 to 0.6 g elemental calcium per day.
References
- Pocket Guide to Diagnostic Tests, 5e by Diana Nicoll, Stephen J. McPhee, Michael Pignone, Chuanyi Mark Lu. © 2010by The McGraw-Hill Companies, Inc
- CURRENT Medical Diagnosis & Treatment 2011 Stephen J. McPhee, Maxine A. Papadakis, Eds. Michael W. Rabow, Associate Ed.© 2011 by The McGraw-Hill Companies, Inc
- Harrison's Principles of Internal Medicine, 17e Anthony S. Fauci, Eugene Braunwald, Dennis L. Kasper, Stephen L. Hauser, Dan L. Longo, J. Larry Jameson, and Joseph Loscalzo, Eds. © 2008 by The McGraw-Hill Companies, Inc.
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