Calcium is a mineral that people obtain from their diets and that is crucial to building and maintaining strong bones and teeth. In addition, calcium is involved in many other body processes, including muscle and blood vessel contraction, regulating the heartbeat and conducting nerve impulses to send messages through the nervous system.

Calcium is the most common mineral found in the body. About 99 percent of calcium is found in the bones and teeth. Smaller amounts are also found in the bloodstream and soft tissues.

The body needs calcium but does not make it, so obtaining appropriate amounts of calcium from the diet is crucial. Milk and dairy products offer the biggest sources of calcium. Other sources include some types of canned fish, green leafy vegetables, and fortified breakfast cereal, cereal bars and orange juice.

A calcium deficiency occurs when people do not have adequate stores of calcium. This can result from inadequate calcium intake, decreased calcium absorption and increased calcium excretion. When the body does not have enough calcium, it draws calcium from the bones, which can cause the bones to weaken, raising the risk of fracture. Calcium deficiency over an extended period of time also increases the risk of loss of bone density known as osteoporosis.

Several factors affect how calcium is absorbed from the digestive tract into the body’s circulation. These include the amount of calcium consumed during a single meal, a person’s age, and the presence of other vitamins (especially vitamin D) and substances in the body.