Vitamin D is a fat-soluble vitamin that occurs in two forms: D2 and D3. Vitamin D3 occurs naturally in the body and is made in the skin under direct sunlight. Vitamin D plays a major role in the development and calcification of bones. Vitamin D is mostly absorbed from diets rich in vitamin D, such as eggs, fish and fortified milk. Vitamin D helps in the absorption of calcium in the intestines. Diseases affecting the intestines may also affect the role of vitamin D in calcium absorption.
Identified Causes
The health of the intestines and sufficient dietary intake are important for adequate calcium absorption in the intestines, which is aided by vitamin D. Diseased intestines, or unhealthy intestines, affect the role of vitamin D in calcium absorption. Ulcerative colitis and Crohn's disease have been associated with vitamin D deficiency.
The liver is intimately involved in vitamin D metabolism; diseases affecting the liver may also affect vitamin D metabolism. Cirrhosis and hepatitis are diseases that have been associated with low vitamin D.
The use of certain medications such as anticonvulsants, or anti-seizure medications, and steroids lead to increased breakdown of vitamin D, thereby causing a dependency on vitamin D supplementation.
In winter months, lack of sun exposure is common and often leads to low levels of vitamin D in the blood.
Possible Complications
Decreased absorption of calcium from the intestines may lead to hypocalcemia, or low blood calcium. Severe hypocalcemia carries serious risks, such as irregularity of heartbeat and seizures. Hypocalcemia is a stimulus for the parathyroid gland to increase secretion of parathyroid hormone; this causes secondary hyperparathyroidism. Sustained vitamin D deficiency can lead to bone softening, which is called osteomalacia in adults or rickets in kids.
Associated Symptoms
In vitamin D deficiency, the bones become fragile and more likely to fracture due to secondary hyperparathyroidism. Individuals will often complain of bone pain and joint pain. Other symptoms that can occur include depression, generalized weakness, abdominal pain and nausea.
The presence of hypocalcemia can lead to tetany, or uncontrollable contraction of muscles. Abnormal sensation on the lips, tongue and fingers is also experienced with tetany. Facial spasms may occur as well. Newborns can get tetany if they are born to mothers deficient in vitamin D during pregnancy.
Testing and Diagnosis
A suspected deficiency of vitamin D can be confirmed by your primary care physician. A nurse draws a blood sample that is tested for concentrations of active vitamin D, or 25OHD. A normal concentration of 25OHD should be above 30 nanograms per milliliter, or ng/mL; below 30 ng/mL is considered abnormal. Vitamin D deficiency is defined as a 25OHD concentration below 20 ng/mL.
Treatment
Individuals with abnormal levels of 25OHD should consider making dietary changes or supplementing vitamin D if necessary. The U.S. Department of Health and Human Services advises supplementation of 700 to 800 international units, or IUs, of vitamin D3 per day with 500 to 1,200 mg of calcium; this combination has proven effective in reducing the chances of fractures.
Sun exposure is highly recommended in conjunction with dietary changes, which should include the intake of eggs, fish, vitamin D-fortified milk and cod liver oil.
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