Mycrocrystalline Hydroxyapatite (MCHA)is a natural compound that makes up the crystalline matrix of bone and teeth, and is the substance that gives them their rigidity. MCHA is a highly absorbable Calcium and Phosphorus, which are the major mineral components of bone. NOW Bone Strength is a comprehensive bone support product providing 4 g (4,000 mg) of MCHA. It also contains Magnesium and Trace Minerals, as well as Vitamins C, D and K to aid in the synthesis and maintenance of bone tissue. All NOW Foods products, like Bone Strength, containing microcrystalline hydroxyapatite calcium is from a New Zealand source and meets Californias stringent Environmental Statute Proposition 65 requirement for the presence of lead being less than .5ppm.