Perhaps surprisingly, the Department of Agriculture lists calcium as one of the four most missing nutrients in the American diet. Approximately 99 percent of that calcium is present in the bones and teeth. Although bones appear to be solid and inert, they are not. Calcium moves in and out of the bones in a complex series of reactions regulated by hormones. Each year, approximately 20 percent of the calcium in bones is removed and replaced.
Some hormones work to ensure that there is enough calcium in the blood.
This means that calcium is readily available to the bones, as well as to nerves and muscles. In the bone matrix, calcium is found as calcium phosphate, and phosphorus is also an essential part of maintaining skeletal health. In 1919, Sir Edward Mellanby found a compound in cod liver oil that helped in rickets, a boneweakening condition notable in young children. The substance became known as vitamin D. Vitamin D is valued for its ability to increase the amount of calcium deposited in the bones. However, all calcium is not found in bones and teeth.