About Calcium Calcium is necessary for cardiac function, muscle contraction, nervous activity, coagulation of blood and for maintaining structural integrity of cell membranes. Plasma concentration of calcium is kept in normal range by three endocrine factors which control metabolism of calcium. These are (a) Parathyroid hormone, (b) Calcitonin, (c) Vitamin D. Calcium in plasma is bound to albumin, is complexed with anions (e.g. phosphate) and as diffusible ionic calcium. The physiological effects are exerted by ionic calcium. The predominant source of calcium is dairy products and the daily intake varies from 200 - 2500 mg. Adequate calcium intake is particularly important during periods of bone growth in childhood and adolescence and during pregnancy and lactation.