The major mechanism whereby calcium effects bone is probably through inhibition of PTH secretion. Many people would like to believe that they could prevent osteoporosis by increasing their calcium intake. Calcium excess does not necessarily result in bone gain or even in prevention of bone loss, but calcium deficiency certainly will make bone loss worse. International calcium intake and fracture Cross-cultural studies have failed to demonstrate any relationship between the customary dietary intake and the incidence of osteoporosis. Although the international patterns of osteoporosis appear to cast doubt on the relationship between calcium intake and osteoporosis, they do not eliminate the possible positive role of calcium.
Hereditary factors are much more important than dietary factors in determining the bone mass.
Also, there can be serious errors in the estimation of calcium intake from the tremendously different diets of different cultures. Tortillas made from corn have high calcium content because the stones used to grind the flour were traditionally made of limestone. In some countries chewing on chicken bones is habitual. The overall impression gained from reviewing these studies is that calcium has a weak positive effect on bone mass. The results of these studies are mixed.