It is a common myth that people should increase their calcium intake. Mostly, they are encouraged to take supplements and to drink more milk. It turns out that keeping strong bones depends more on preventing calcium loss than on increasing calcium intake. Almost all of the calcium in the body is in the bones. There is a tiny amount in the blood stream which is responsible for muscle contraction, maintenance of the heartbeat, and transmission of nerve impulses and other functions.
Hormones control the amount of calcium in the blood.
Everyone constantly loses calcium through urine, sweat, and feces, and it is renewed with calcium from the bones. In the process, the body constantly breaks down and rebuilds bones. Ultimately, the body's calcium is replaced by calcium from food. Since the 1920's researchers have known that diets that are high in protein, especially animal protein, cause calcium to be lost through the urine. Vegetarians have lower rates of osteoporosis than meat eaters.