The synthesis of vitamin D takes place in the skin under direct sunlight. Vitamin D exists in two forms: D2 and D3. Vitamin D3 occurs naturally and has a role in the development and calcification of bones. Vitamin D is absorbed in the gut and also helps in the absorption of calcium. Low vitamin D leads to hypocalcemia, or low blood calcium. Secondary hyperparathyroidism, or elevated parathyroid hormone release, can result from hypocalcemia.
Parathyroid Hormone
The parathyroid gland is important in the regulation of calcium in the blood. It releases parathyroid hormone when it detects a decrease in calcium in the blood. The parathyroid hormone causes the breakdown of bone, thereby releasing calcium into the blood. It also inhibits the loss of calcium in the urine. Vitamin D deficiency results in hypocalcemia; hypocalcemia stimulates the parathyroid gland. Secondary hyperparathyroidism results from excess secrection of parathryoid hormone due to hypocalcemia, which is a complication of vitamin D deficiency.
Possible Complications
Vitamin D-associated hypocalcemia may cause an irregular pulse; it can also cause seizures. Severe hypocalcemia has been reported to cause irreversible heart failure. Vitamin D deficiency causes poor mineralization of bone, which leads to diseases of bone softening such as osteomalacia and rickets. In secondary hyperparathryoidism, the action of parathyroid hormone makes the bone more fragile. Increased fragility of bones increases the likelihood of fractures.
Associated Symptoms
Bone and joint pain are chief complaints associated with secondary hyperparathyroidism. Other symptoms may include generalized weakness, depression, nausea and abdominal pain.
Tetany may result from hypocalcemia. Tetany is a condition of uncontrollable muscle contractions that causes unfamiliar sensations over the lips, tongue and fingers. The muscles of the face also tend to twitch randomly.
Diagnosis
Adequate history taking by a physician should provide clues to vitamin D deficiency. To confirm vitamin D deficiency it is necessary to collect a blood sample that will be tested in the lab for concentration of active vitamin D or 25OHD. The concentration of 25OHD in the blood is adequate if it is greater than 30 nanograms per milliliter, or ng/mL, less than 30 ng/mL is considered abnormal. A 25OHD concentration less than 20 ng/ml is defined as Vitamin D deficiency.
Treatment and Management
The U.S. Department of Health and Human Services advices the use of vitamin D at doses of 700 to 800 international units, or IUs, with 500 to 1,200 mg of calcium. This combination has proven to reduce the likelihood of fractures. Age, degree of bone health and the severity of vitamin D deficiency are factors that determine aggressiveness of management and treatment. An elder who is prone to falls should be cautious to avoid vitamin D deficiency as it increases the risk of injury associated with falls.
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