Calcium is the most common mineral found in the body. It is necessary to build and maintain strong bones and teeth and aids other body processes. On average, calcium makes up about 3 pounds (1.36 kilograms) of the body weight of a person who weighs 130 pounds (59 kilograms).  

Almost all calcium in the body is stored in a person’s bones. This mineral helps bones to remain strong and stiff enough to carry the weight of the body and to protect internal organs. Calcium in the bones also serves as a storehouse for the mineral when it is needed elsewhere, such as in the bloodstream and soft tissues. Calcium helps many body processes, including muscle and blood vessel contraction, blood clotting, enzyme and hormone secretion and helps the central nervous system to function.

Consuming appropriate levels of calcium is crucial because the body does not make its own calcium. In addition, the body needs a constant supply of calcium to keep bones growing and strong. Bone remodeling is an ongoing process in which bone is broken down (resorbed) and calcium is deposited to replace the bone material that is lost (bone formation). When the amount of calcium in the bloodstream is low, calcium from bone is broken down and is used in the bloodstream. This can deplete the calcium in bones, a process that may take many years.

During childhood, people undergo a greater amount of bone formation and less bone breakdown. Formation and breakdown are relatively equal during early and middle adulthood. After age 35, more bone is lost than is replaced. Bone loss especially accelerates in women following menopause. People can continue to build bone mass until their mid-30s. After that, they can only slow the bone loss that is a natural part of aging.

By consuming adequate levels of calcium early in life, people can build up a maximum amount of bone that will help protect them later in life when their bones inevitably begin to lose more calcium than they replace. Weight-bearing exercise (e.g., walking, running) throughout the lifespan helps to maximize bone strength and bone density (the amount of bone tissue in a certain volume of bone).

Children and adolescents especially should try to build peak bone mass. This can help reduce the risk of fractures and osteoporosis later in life. By the time a child’s growth spurt ends in the later teen years, 90 percent of adult bone mass already has been established, although bone mass continues to gradually build before peaking in a person’s 30s. Children who do not consume adequate levels of calcium cannot make up for this missed opportunity later in life. Fewer than one in 10 girls and only one in four boys ages 9 to 13 are at or above their adequate intake of calcium, according to the National Institutes of Health (NIH).

Although people cannot continue to build new bone after their 30s, adequate calcium intake and engaging in weight-bearing exercises can help them to hold on to the bone mass that they already have developed. Experts also urge people to get enough vitamin D in their diets because this vitamin is necessary to absorb calcium. Milk that is fortified with vitamin D is a good source of this nutrient.  Other sources include vitamin D fortified yogurt and vitamin D fortified ready-to-eat breakfast cereals.

The Institute of Medicine (IOM) of the National Academy of Sciences has issued the following daily calcium intake guidelines, expressed in milligrams (mg):

Experts generally recommend that a person over the age of one year not consume more than 2,500 milligrams of calcium per day. Excessively high intakes of calcium can result in hypercalcemia (elevated levels of calcium in the blood), impaired kidney function and decreased absorption of other minerals. However, contrary to earlier belief, increased calcium consumption does not appear to cause increased formation of kidney stones.