Your body and calcium

Calcium is an important mineral that our bodies need. Having cancer can affect the amount of calcium in the body.

Why our bodies need calcium

Nearly all the calcium in the body is stored in bone tissue. But a small amount (around 1%) circulates dissolved in the blood and other body fluids or is inside our cells.

This is needed for:

  • keeping bones and teeth healthy
  • blood clotting
  • normal functioning of the brain and spinal cord (central nervous system)
  • keeping our muscles working properly

Blood calcium levels that are too high or too low can be dangerous. Having too much calcium in the blood is called hypercalcaemia (pronounced hyper-kal-seem-ia). Not having enough calcium is called hypocalcaemia (hypo-kal-seem-ia).

Where we get calcium from

Our diet gives us calcium. The foods highest in calcium include:

  • dairy products such as eggs, milk, butter and cheese – this is where most of our calcium comes from
  • green vegetables such as broccoli, spinach and beans
  • nuts

What happens to calcium in the body

Our bodies absorb calcium from the food we eat through the lining of the bowel. The calcium is stored in our bones. The body controls the amount of calcium in the bloodstream very carefully. When blood levels of calcium fall too low, the bones release calcium into the blood. The amount of calcium the bowel absorbs from food increases and the kidneys get rid of less calcium through the urine.

The opposite happens if blood levels of calcium get too high.

There are 3 hormones in the body that play an important role in this complicated control system. These are:

  • parathyroid hormone (PTH) – made by the parathyroid glands in the neck
  • calcitonin
  • vitamin D

These hormones help to keep the correct balance of calcium in the blood.

If this balance is upset, the amount of calcium in our blood can get too high (hypercalcaemia) and cause serious problems.

The main causes of hypercalcaemia are:

  • too much calcium leaking out of the bones into the blood
  • your kidneys not being able to get rid of excess calcium
  • taking in too much calcium from the food we eat

Some cancers produce hormones that make too much calcium in the body.

Normal calcium levels

The level of calcium in the blood is normally between 2.1 mmol per litre and 2.6 mmol per litre. But remember that blood levels can vary a little from person to person.

You might need treatment if your calcium level goes above or below these levels.

Last reviewed: 
14 Nov 2018
  • Cancer and its management (7th edition)
    J Tobias and D Hochhauser
    Wiley-Blackwell, 2015

  • Ross and Wilson anatomy and physiology in health and illness (12th edition)

    A Waugh and A Grant

    Elsevier, 2014

  • Diagnosis and management of hypocalcaemia

    BMJ, 2008

  • Hypercalcaemia of Malignancy

    BMJ Best Practice, December 2018

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