Calcitonin is a hormone protein that lowers the concentration of blood calcium when it has risen to an above normal level. In humans and other mammals, calcitonin is secreted by the parafollicular cells of the thyroid gland while in fish, birds and reptiles it is secreted by the ultimobranchial gland.
The main actions of calcitonin are the lowering of blood calcium and the suppression of cell activity that causes calcium to be lost from bones. Some of the main actions of calcitonin are described below:
- In postmenopausal women with osteoporosis - Osteoporosis leads to brittle and easily fractured bones as a result of decreased bone mass along with architectural breakdown of the bones. Common fracture sites include the vertebrae, hip, forearm and wrist. The most common type of osteoporosis occurs in postmenopausal females, when the rate of bone resorption by osteoclasts is faster than the rate of bone formation by the osteoblasts. The use of manufactured calcitonin can inhibit osteoclast activity in these patients.
- Maintenance of calcium balance in the body - Calcitonin opposes the effects of parathyroid hormone, which acts to increase the blood calcium level. Calcitonin lowers blood calcium levels by suppressing osteoclast activity in the bones and increasing the amount of calcium excreted in the urine.
- Effects on the kidney - Calcitonin also regulates the level of calcium and other minerals in the kidneys. This hormone prevents the re-absorption of phosphates by the kidney and increases the kidney’s re-absorption of calcium and magnesium.
- Calcitonin also affects hunger and appetite and has been shown to reduce the volume and acidity of gastric juice, as well as the volume of the pancreatic juice and its trypsin and amylase content
Pharmacokinetics of calcitonin
Calcitonin-containing medicines are usually administered as solutions that can be injected but for the past couple of decades, they have also been available in the form of nasal sprays.
When used as a nasal spray, calcitonin takes around 13 to 15 minutes to be absorbed into the blood. The half-life of commercially prepared calcitonin is around 18 to 20 minutes.
Calcitonin as a treatment
Calcitonin may be used to treat several conditions. Some examples of these include:
- Postmenopausal osteoporosis – This is the most common indication for the use of calcitonin medication. Women with low bone mass more than 5 years after menopause are often prescribed a nasal spray, which is to be taken along with calcium (at least 1000 mg elemental calcium per day) and vitamin D (400 I.U. per day).
- Paget’s disease – In this condition, the repair and renewal of bone is disrupted, causing bone deformity.
- Cancer – Calcitonin is used to reduce the increased calcium levels caused by various cancers once they are in the advanced stages.
Calcium loss from bones
Calcitonin prevents calcium loss from bones, which is particularly important in cases of health conditions that tend to cause this loss such as pregnancy or being immobilized for a prolonged period due to a fracture or heart attack, for example.
Side effects of calcitonin
- Nasal spray use is associated with side effects such as runny nose and nasal crusting, dryness, bleeding itching and redness. The majority of these symptoms are mild and resolve as a patient adjusts to using the spray.
- There may be symptoms that mimic flu such as tiredness, fever and chills
- Skin rash
- Muscle pain and arthritis
- Sinusitis, chest tightness, difficulty breathing
- High blood pressure, chest pain, palpitations
- Abdominal pain, nausea, diarrhea, vomiting, flatulence and decreased appetite
- Increased urination
Reviewed by Sally Robertson, BSc