ABSTRACT
Calcium is the fifth most abundant element on the globe. It is found in a variety of rocks and throughout most waters. The adult human body contains about 1 kg of calcium, over 99% of which is found in the skeleton in solid form. Calcium that enters the small intestine is absorbed via two independent routes, transcellular and paracellular. The transcellular route involves three sequential steps: calcium entry, intracellular diffusion, and calcium extrusion. The plasma calcium is in extremely rapid, dynamic equilibrium with calcium in the extracellular fluid. Calcium in the stool originates from two sources: food calcium that has escaped intestinal absorption and endogenous calcium that also has escaped absorption. Muscles and weight-bearing bones exist in an intimate relationship to one another. Calcium intakes between 1.0 and 1.5 g are considered adequate to ensure appropriate bone health if there are no other health problems, such as gonadal deficiency.
