Calcitonin is a hormone that is produced in humans by the parafollicular cells (commonly known as C-cells) of the thyroid gland. Calcitonin is involved in helping to regulate levels of calcium and phosphate in the blood, opposing the action of parathyroid hormone. This means that it acts to reduce calcium levels in the blood. However, the importance of this role in humans is unclear, as patients who have very low or very high levels of calcitonin show no adverse effects.
Calcitonin reduces calcium levels in the blood by two main mechanisms:
Manufactured forms of calcitonin have, in the past, been given to treat Paget’s disease of bone and sometimes hypercalcaemia and bone pain. However, with the introduction of newer drugs, such as bisphosphonates, their use is now very limited.
The secretion of both calcitonin and parathyroid hormone is determined by the level of calcium in the blood. When levels of calcium in the blood increase, calcitonin is secreted in higher quantities. When levels of calcium in the blood decrease, this causes the amount of calcitonin secreted to decrease too.
There does not seem to be any direct deleterious effect on the body as a result of having too much calcitonin.
Medullary thyroid cancer is a rare type of cancer that arises from the C-cells in the thyroid gland that secrete calcitonin. It is sometimes associated with multiple endocrine neoplasia type 2a and multiple endocrine neoplasia type 2b. Patients with medullary thyroid cancer have high calcitonin levels in their bloodstream. However, it is important to note that these high calcitonin levels are a consequence of this condition, not a direct causal factor.
There does not seem to be any clinical effect on the body as a result of having too little calcitonin. Patients who have had their thyroid gland removed, and have undetectable levels of calcitonin in their blood, show no adverse symptoms or signs as a result of this.
Last reviewed: Feb 2018