Multimedia

In addition to building strong bones, calcium is crucial for the transmission of nerve signals and other functions. If there isn't enough calcium in your blood, your parathyroid glands secrete a hormone that triggers:

  • Your bones to release calcium into your blood
  • Your digestive tract to absorb more calcium
  • Your kidneys to excrete less calcium and activate more vitamin D, which plays a vital role in calcium absorption

This delicate balance between too much and too little calcium in your blood can be disrupted by a variety of factors. Hypercalcemia may be caused by:

  • Overactive parathyroid glands. The most common cause of hypercalcemia, overactive parathyroid glands (hyperparathyroidism) may stem from a small noncancerous tumor on one or more of the four parathyroid glands.
  • Cancer. Lung cancer and breast cancer, as well as some cancers of the blood, can increase your risk of hypercalcemia. Spread of cancer (metastasis) to your bones also increases your risk of hypercalcemia.
  • Other diseases. Certain diseases, such as tuberculosis and sarcoidosis, may raise blood levels of vitamin D, which stimulates your digestive tract to absorb more calcium.
  • Immobility. People with cancer or other diseases that cause them to spend a great deal of time sitting or lying down may develop hypercalcemia. Over time, bones that don't bear weight release calcium into the blood.
  • Medications. Certain drugs — such as lithium, which is used to treat bipolar disorder — may increase the release of parathyroid hormone.
  • Supplements. Taking excessive amounts of calcium or vitamin D supplements over time can raise calcium levels in your blood above normal.
  • Hereditary factors. A rare genetic disorder known as familial hypocalciuric hypercalcemia causes an increase of calcium in your blood because of faulty calcium receptors in your body.
  • Dehydration. A common cause of mild or transient hypercalcemia is dehydration, because when there is less fluid in your blood, calcium concentrations rise.
Apr. 25, 2014

You Are ... The Campaign for Mayo Clinic

Mayo Clinic is a not-for-profit organization. Make a difference today.