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 regulating levels of calcium and phosphate in the blood. It works by opposing the action of parathyroid hormone, which 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.
The secretion of calcitonin is also inhibited by the hormone somatostatin, which can also be released by the C-cells in the thyroid gland.
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 rather than a cause of this cancer.
There does not seem to be any clinical effect on the body as a result of having too little calcitonin as other hormones, particularly parathyroid hormone (PTH), are more important for regulating blood calcium levels. 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: Nov 2021