Vitamin D Deficiency & Parathyroid Hormones

Vitamin D is made under the skin by sunlight. Vitamin D works in the intestines, causing the absorption of calcium and phosphorus from food. The actions of vitamin D promote bone calcification and development. Vitamin D also inhibits the secretion of the parathyroid hormone by helping the absorption of calcium in the intestines. The parathyroid hormone causes the breakdown of bone for the purposes of releasing calcium to the blood.

Parathyroid Hormone and Calcium Regulation

The parathyroid hormone, or PTH, is a product of the parathyroid glands, which are located next to the thyroid gland. The parathyroid gland regulates calcium in the blood by releasing the parathyroid hormone. When parathyroid hormone is released, it stimulates cells that break down bone and increase reabsorption of calcium from the kidneys. The aim of parathyroid hormone is to boost the concentration of calcium in the blood. The parathyroid gland is inhibited by high calcium in the blood. Hypocalcemia, or low blood calcium, stimulates the parathyroid gland to release more parathyroid hormone; this is called secondary hyperparathyroidism.

Complications of Vitamin D Deficiency

Hypocalcemia is a direct complication of vitamin D deficiency; it can lead to secondary hyperparathyroidism. Hypocalcemia and hyperparathyroidism in combination is bad news for bone health--they decrease bone density and thereby decrease bone strength. Vitamin D deficiency over time can lead to bone softening. Bone softening in adults is called osteomalacia; in children it's called rickets.

Observed Symptoms

Secondary hyperparathyroidism makes your bones fragile, thus increasing the likelihood of a fracture. Individuals often complain of bone and joint pain. Depression, abdominal pain, weakness and nausea are all symptoms associated with hyperparathyroidism.

Vitamin D-associated hypocalcemia can cause tetany, which is a disorder that causes uncontrollable muscle contractions. Tetany can create abnormal sensation over your fingers, tongue and lips. Abnormal facial muscle contractions may be seen. Neonates born to mothers with vitamin D deficiency can also have tetany.

Evaluation

Your physician may order an evaluation for vitamin D deficiency. A nurse then will draw a blood sample from your arm using a small-gauge needle. The sample of blood is then tested for the concentration of active vitamin D, or 25OHD; it is the concentration of 25OHD that determines whether an individual is adequate or deficient in vitamin D. When 25OHD is above 30 ng/mL of blood, it's concentration is normal in the blood; below 20 ng/mL indicates vitamin D deficiency. Borderline concentrations of 25OHD fall between 30ng/mL and 20 ng/mL.

Treatment and Management

Hypocalcemia and secondary hyperparathyroidism result from vitamin D deficiency; to treat these conditions it is necessary to address the vitamin D deficiency. Individuals with vitamin D deficiency have a concentration of 25OHD that is less than 20 ng/mL; for these individuals, dietary modifications and vitamin D supplementation are both recommended. The U.S. Department of Health & Human Services confirms that the use of 700 IU to 800 IU of vitamin D3 per day, with 500 to 1,200 mg of calcium, is effective in reducing the risk for fractures. The reduced risk for fractures implies an increase in bone density supported by increases in 25OHD concentration in the blood.