ESC® brand calcium from eggshells is a naturally pure calcium source compliant with FDA, USP, and California Proposition 65 limits for heavy metals at the full 1,000 mg dose of elemental calcium per day. ESC is highly absorbable – its matrix consists of an ultra-pure form of calcium carbonate with high elemental calcium content, inherent transport proteins to help facilitate calcium absorption, and many trace minerals which the body needs to maintain healthy bone health.* This translates into a superior source of calcium over other bone health ingredients.