Calcium is the most abundant mineral in the body. More than 99 percent of the calcium in the body can be found in the bones and the teeth. The body is constantly adding and reabsorbing calcium from the bones—think of the bones as sort of like a calcium bank.
The calcium balance tends to shift over time. More calcium is deposited than withdrawn in youth, while after 40 years of age, particularly in women, the body withdraws more calcium than it deposits. Hence, calcium requirements tend to increase with age.
Note that your potassium consumption is important too, as potassium also helps conserve the body's calcium and improve bone density. This is possible because many potassium-containing fruits and vegetable are alkaline, rather than acidic (like fish, meat and dairy). An overly acidic body may mobilize alkaline calcium salts from bones to bring the body to a normal pH, thus depleting bones of calcium. Eating enough potassium will mean the body can maintain a normal pH without withdrawing calcium from the bones.
How much you should have: Most adults need 1,000 mgs of calcium a day. Adults over the age of 50 and post-menopausal women should have 1,300 mgs of calcium a day.