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Current science supports the view that calcium is mainly absorbed in an ionized state in the small intestine through calcium
channels in the enterocyte plasma membranes. Vitamin D3 stimulates the induction of calcium-binding proteins, enhancing calcium
ion absorption via those channels.
An isotonic calcium preparation does not require lengthy dissolution in the stomach like a tablet, since the calcium and
magnesium are largely in an ionized state. An isotonic product is sophisticated in its delivery system as compared to tablets
or capsules. Note that the small intestine (and the very first part of the colon) can only absorb about 300-400 mg of calcium
at a meal or from supplementation. The remainder is excreted in the feces.
References
Schaafsma, G., Bioavailabilty of Calcium and Magnesium, European Journal of Nutrition 1007;51:S13-16.
Levenson, D.I., Bockman, R.S., A Review of Calcium Preparations, Nutrition Reviews 52: 221-232, 1994.
Seigel, J.A. Biphasi nature of gastric emptying. Gut 29: 35-39, 1988
Sladen, G.E. In: Transport across the Intestine. W.L. Burland and P.D. Samuel(eds.). New York: Academic Press., 1972.
Graham, D.Y., J.L.Smith, and A.A. Bouvet. What happens to tablets in the stomach. Journal of Pharmaceutical Sciences 79(5): 420-424, 1990.
Hunt, J.N. Properties of and alimentary osmoreceptor mechanism. Journal of Physiology (London) 132:267-288,1965.
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