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Title: IMPROVED ESTIMATION OF THE CALCIUM CONTENT OF TOTAL DIGESTIVE SECRETIONS

Author
item HEANEY, ROBERT - CRIGHTON UNIVERSITY
item Abrams, Steven

Submitted to: Journal of Clinical Endocrinology and Metabolism
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/1/2003
Publication Date: 3/1/2004
Citation: Heaney, R.P., Abrams, S.A. 2004. Improved estimation of the calcium content of total digestive secretions. Journal of Clinical Endocrinology and Metabolism. 89(3):1193-1195.

Interpretive Summary: Little is known about the determinants of endogenous entry of calcium into the gut (TIC). It does not seem to be invluenced by the usual calcium hemeostatic indicators, but is, instead, more a function of the size (and to some extent perhaps the composition) of the food load that the gut must process. We had earlier reported from two different data sets, that the TIC rises with phosphorus intake (as well as with body size and some measures of total food intake). That correlation remains true for this expanded data set. This relationship may be the explanation for why, in experimental animals such as dogs, whose diets typically exhibit very high phosphorus densities, endogenous fecal calcium loss is quantitatively a much more important route of loss from the body than is urine calcium. In adult humans, by contrast, TIC and urine calcium are of approximately equal magnitude.

Technical Abstract: Because endogenous fecal calcium (EFC) excretion plays a larger role in the calcium economy of adults than does actual calcium intake, and because at typical absorption efficiencies, EFC is largely determined by endogenous entry of calcium into the gut (TIC), it is important to be able to quantify TIC when studying the effect of nutrients, drugs, and disease on body calcium handling. Measured values for EFC derived from 553 balance studies in middle-aged women (mean: 48.8 yrs) were pooled with 76 values obtained from premenarcheal girls (mean: 11.2 yrs), after adjusting for differences in body size. The aggregate sample provided values for calcium absorption efficiencies spanning a range from under 10% to over 90%. EFC is known to be inversely related to calcium absorption (AbsFx), and the broad range of absorption eficiencies allowed derivation of reasonably precise estimates of EFC at zero and 100% absorption. These were, respectively 0.8067 mg/cm height/day (+- 0.0143) and 0.1799 mg/cm height/day (+- 0.0310). At zero absorption EFC is identical to the total entry of calcium into the intestine from endogenous sources (secretions plus sloughed mucosa), while at 100% absorption, EFC measures only endogenous entry distal to the absorptive surface. The partition described facilitated derivation of a formula to calculate TIC for any values for EFC and AbsFx, i.e., TIC = EFC/[0.223 + 0.777 (1 - AbsFx)].