Calcium carbonate, calcium derived from bone meal, oyster shell, or dolomite are VERY likely to contain lead, and you don't want that. Most of the calcium in the body is bone. But providing skeletal material is far from calcium's only role in the body.
Calcium serves in nerve transmission, muscular contraction, and blood clotting.
It is easy to see why dietary calcium is important in maintaining proper bone density. The common female complaints of PMS and symptoms of menopause may be relieved by simple supplementation with the mineral, calcium. You Do NOT Want Osteoporsis Osteoporosis is a term familiar to most people. But the time to combat it is now. We have all seen the little old ladies whose vertebrae have collapsed from lack of calcium, making them shorter and hunched over.