Calcium is vital for muscle contraction in the skeletal muscles, as well as for the heart's blood-pumping action, blood vessel contraction and vasodilation. The mineral is also involved in nerve impulse transmission and blood clotting, as well as tooth formation and maintenance. Pure Lab Vitamins Microcrystalline Calcium Hydroxyapatite (MCHA) contains more than just calcium. It's an organically-bound complex of what's naturally part of the bone matrix: bone growth factors, proteins, mucopolysaccharides, calcium, phosphorus, and trace minerals. Together, these are needed for the maintenance of healthy bones, teeth and systemic cellular functions. With its superior bioavailability over calcium carbonate and other popular calcium compounds, calcium hydroxyapatite supports the bone mineral matrix in its entirety. Its natural phosphorus content is vital to the balance and utilization of vitamin D, iodine, magnesium and zinc, as well as for the production of the phosphates used in cellular membrane function, energy, and DNA.