Calcitonin

Calcitonin is a hormone that is produced and released by the C-cells of the thyroid gland. Its biological function in humans is to have a relatively minor role in calcium balance.

Alternative names for calcitonin

What is calcitonin?

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:

1. It inhibits the activity of osteoclasts, which are the cells responsible for breaking down bone. When bone is broken down, the calcium contained in the bone is released into the bloodstream. Therefore, the inhibition of the osteoclasts by calcitonin directly reduces the amount of calcium released into the blood. However, this inhibition has been shown to be short-lived.
2. It can also decrease the reabsorption of calcium in the kidneys, again leading to lower blood calcium levels.

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.

How is calcitonin controlled?

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.

What happens if I have too much calcitonin?

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.

What happens if I have too little calcitonin?

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.