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Overview of Calcium's Role in the Body

By

James L. Lewis III

, MD, Brookwood Baptist Health and Saint Vincent’s Ascension Health, Birmingham

Reviewed/Revised Sep 2023
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About 99% of the body’s calcium is stored in the bones, but cells (particularly muscle cells) and blood also contain calcium. Calcium is essential for the following:

  • Formation of bone and teeth

  • Muscle contraction

  • Normal functioning of many enzymes

  • Blood clotting

  • Normal heart rhythm

The body precisely controls the amount of calcium in cells and blood. The body moves calcium out of bones into blood as needed to maintain a steady level of calcium in the blood. If people do not consume enough calcium, too much calcium is mobilized from the bones, weakening them. Osteoporosis Osteoporosis Osteoporosis is a condition in which a decrease in the density of bones weakens the bones, making breaks (fractures) likely. Aging, estrogen deficiency, low vitamin D or calcium intake, and... read more Osteoporosis , which is a decrease in bone density that can result in bone fractures, can result. To maintain a normal level of calcium in the blood without weakening the bones, adults need to consume at least 1,000 to 1,300 milligrams of calcium a day. Vitamin D is also needed to help absorb calcium. Adults should consume 600 units of vitamin D a day (or 800 units in older adults).

The level of calcium in blood is regulated primarily by two hormones:

  • Parathyroid hormone

  • Calcitonin

Parathyroid hormone is produced by the four parathyroid glands, located around the thyroid gland Overview of the Thyroid Gland The thyroid is a small gland, measuring about 2 inches (5 centimeters) across, that is located just under the skin in the neck. The two halves (lobes) of the gland are connected in the middle... read more in the neck. When the calcium level in blood decreases, the parathyroid glands produce more parathyroid hormone. When the calcium level in blood increases, the parathyroid glands produce less hormone. Parathyroid hormone does the following:

  • Stimulates bones to release calcium into blood

  • Causes the kidneys to excrete less calcium in urine

  • Stimulates the digestive tract to absorb more calcium

  • Causes the kidneys to activate vitamin D, which enables the digestive tract to absorb more calcium

Calcitonin is produced by cells of the thyroid gland. It lowers the calcium level in blood by slowing the breakdown of bone, but only slightly.

More Information

The following English language resources provide information that may be useful. THE MANUAL is not responsible for the content of these resources.

  • National Institutes of Health Office of Dietary Supplements: Calcium Fact Sheet for Consumers: provides a general overview of calcium, including its role in the body and daily nutrition requirements

  • National Institutes of Health Office of Dietary Supplements: Vitamin D Fact Sheet for Consumers: provides a general overview of vitamin D, including its role in the body and daily nutrition requirements

NOTE: This is the Consumer Version. DOCTORS: VIEW PROFESSIONAL VERSION
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