Between 10-40% of dietary calcium intake is absorbed although women after menopause may only absorb 7%. Calcium from milk and milk products is absorbed more easily than that from vegetables. Absorption is enhanced by vitamin D, proteins, lactose and stomach acid.Lactation increases the ability of women to absorb calcium after weaning or the resumption of menstrual periods. Deficiency and moderate exercise also increase absorption and the efficiency of absorption decreases as intake increases.Dietary calcium must be made soluble in the stomach and then pass to the small intestine where it combines with a calcium binding molecule so it can be absorbed (chelation). Calcium competes with zinc, manganese, magnesium, copper and iron for absorption in the intestine and a high intake of one can reduce absorption of the others.Adults excrete 400-600mg of calcium daily.
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