/" 1 alcium is an essential element in the human body. Although over 1 99% of the total body calcium is located in bone, calcium is a V^y' critical cation in both the extracellular and intracellular spaces. Its concentration is held in a very narrow range in both spaces. In addition to its important role in the bone mineral matrix, calcium serves a vital role in nerve impulse transmission, muscular contraction, blood coagulation, hormone secretion, and intercellular adhesion. Calcium also is an important intracellular second messenger for processes such as exocytosis, chemotaxis, hormone secretion, enzymatic activity, and fertilization. Calcium balance is tightly regulated by the interplay between gastrointestinal absorption, renal excretion, bone resorption, and the vitamin D-parathyroid hormone (PTH) system [1-7].

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