Calcium plays a vital role in muscle contraction. It is also necessary for heartbeat regulation through its effects on heart muscle. It is essential for nerve impulse conduction. It plays a role in the release of neurotransmitters and activates some enzymes which generate neurotransmitters. Calcium also interacts with sodium, potassium and magnesium to regulate blood pressure and water balance. And it plays a role in the activation of prothrombin (which is formed from vitamin K in the liver) which is essential to the blood clotting process. Calcium is essential for cell division, healthy immune function, for enzyme activity and for the production and activity of hormones involved in digestion, energy and fat metabolism, and the production of saliva. It is also involved in the transport of nutrients and other substances across cell membranes.