Calcium is one of the body's electrolytes, which are minerals that carry an electric charge when dissolved in body fluids such as blood, but most of the body's calcium is uncharged. (See also Overview of Electrolytes.)
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, 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 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.
Too little calcium in the blood is called hypocalcemia. Too much calcium in the blood is called hypercalcemia.
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
