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Absorbing Calcium

Creighton University, Omaha, Nebraska 68178

Calcium nutrition not only is widely recognized as important for bone health, but also has been implicated in such disorders as hypertension, preeclampsia, premenstrual syndrome, and colon cancer. In all but the last of these, the amount of calcium actually absorbed across the intestinal mucosal barrier is what counts. Largely because calcium was a surfeit nutrient in the environment in which hominids evolved, our physiologies are optimized to prevent toxicity, rather than to deal with what would have been only intermittent scarcity. As a consequence, gross calcium absorption efficiency is low—averaging ~30% at 300-mg loads for foods with good bioavailability. Because of the high calcium content of digestive secretions, net absorption is substantially lower still—generally between 10% and 20%.

These summary figures hide a great deal of variability. In healthy women, gross absorption efficiency spans at least a threefold range, from 15% to 45%, even after adjustment for differences in intake (1); patients with various metabolic or digestive disorders may absorb at values outside these limits. What such a range means can be illustrated as follows. A woman absorbing at 45% efficiency extracts 135 mg of the calcium in an 8-ounce serving of milk and, after subtracting digestive juice calcium, nets ~100 mg. A woman with gross absorption of 15%, however, extracts only 45 mg and, after allowing for digestive juice calcium, nets 10 mg or less, barely one-tenth as much.

The reasons for much of this interindividual variability are still unclear; nevertheless, it is known that there is a high degree of within-individual consistency in absorptive performance over time, i.e., some individuals are efficient absorbers and others are poor absorbers (2). Thus, whether a person's calcium intake is adequate or not may depend on where he or she falls within this range of absorptive efficiencies. . . . [Full Text of this Article]

References

The following articles in journals at HighWire Press have cited this article:

				J. E. Kerstetter, K. O. O'Brien, and K. L. Insogna Low Protein Intake: The Impact on Calcium and Bone Homeostasis in Humans J. Nutr., March 1, 2003; 133(3): 855S - 861. [Abstract] [Full Text] [PDF]

				S. DeSantiago, L. Alonso, A. Halhali, F. Larrea, F. Isoard, and H. Bourges Negative calcium balance during lactation in rural Mexican women Am. J. Clinical Nutrition, October 1, 2002; 76(4): 845 - 851. [Abstract] [Full Text] [PDF]

				R. P. Heaney, M. S. Dowell, and R. L. Wolf Estimation of True Calcium Absorption in Men Clin. Chem., May 1, 2002; 48(5): 786 - 788. [Full Text] [PDF]

				M. Dijkgraaf-ten Bolscher, J. C. Netelenbos, R. Barto, and W. J.F. van der Vijgh Strontium as a Marker for Intestinal Calcium Absorption: The Stimulatory Effect of Calcitriol Clin. Chem., February 1, 2000; 46(2): 248 - 251. [Abstract] [Full Text] [PDF]