Calcium is an essential nutrient found in many foods, such as dairy products. The bones and teeth contain over 99% of all calcium in the human body.

Bones are always breaking down and rebuilding. Calcium is needed for this process, but the concentration of calcium in the body tends to decline with age. Taking extra calcium helps the bones rebuild and stay strong. The heart, nerves, and blood-clotting systems also need calcium.

People commonly take calcium by mouth for the treatment and prevention of low calcium levels, muscle cramps, osteoporosis, softening of the bones, and PMS. It is also used for high blood pressure, cancer, stroke, and many other conditions, but there is no good scientific evidence to support many of these other uses.

In the US and Canada, foods that contain calcium and vitamin D are allowed to state that they might reduce the risk of osteoporosis.