More than 99% of calcium in the body is in the form of calcium hydroxyapatite, an inorganic matrix of calcium and phosphate that is stored in the bones and teeth. Īlmost all (98%) calcium in the body is stored in the bones, and the body uses the bones as a reservoir for, and source of, calcium to maintain calcium homeostasis. Vitamin D is required for calcium to be absorbed in the gut by active transport and to maintain adequate calcium levels in blood. Active transport is responsible for most absorption when calcium intakes are lower, and passive diffusion accounts for an increasing proportion of calcium absorption as intakes rise. Ĭalcium from foods and dietary supplements is absorbed by both active transport and by passive diffusion across the intestinal mucosa.

The small ionized pool of calcium in the circulatory system, extracellular fluid, and various tissues mediates blood vessel contraction and dilation, muscle function, blood clotting, nerve transmission, and hormonal secretion. IntroductionĬalcium, the most abundant mineral in the body, is found in some foods, added to others, present in some medicines (such as antacids), and available as a dietary supplement.Ĭalcium makes up much of the structure of bones and teeth and allows normal bodily movement by keeping tissue rigid, strong, and flexible. For a reader-friendly overview of Calcium, see our consumer fact sheet on Calcium. This is a fact sheet intended for health professionals.

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