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The ‘anomalous’ absorption of labelled and unlabelled vitamin C in man

Published online by Cambridge University Press:  08 March 2007

Leslie J. C. Bluck*
Affiliation:
MRC Human Nutrition Research, Fulbourn Road, Cambridge, CB1 9NL, UK
Kerry S. Jones
Affiliation:
MRC Human Nutrition Research, Fulbourn Road, Cambridge, CB1 9NL, UK
W. Andy Coward
Affiliation:
MRC Human Nutrition Research, Fulbourn Road, Cambridge, CB1 9NL, UK
Christopher J. Bates
Affiliation:
MRC Human Nutrition Research, Fulbourn Road, Cambridge, CB1 9NL, UK
*
*Corresponding author: Dr Les Bluck, fax +44 (0) 1223 437515, email [email protected]
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Abstract

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Previous studies of vitamin C absorption in man using stable isotope probes have given results which cannot easily be reconciled with those obtained using non-isotope measurement. In order to investigate some of the apparent paradoxes we have conducted a study using two consecutive doses of vitamin C, one labelled and one unlabelled, given 90 min apart. Compatibility of the experimental results with two feasible models was investigated. In Model 1, ingested vitamin C enters a pre-existing pool before absorption, which occurs only when a threshold is exceeded; in Model 2, ingested vitamin C is exchanged with a pre-existing flux before absorption. The key difference between these two models lies in the predicted profile of labelled material in plasma. Model 1 predicts that the second unlabelled dose will produce a secondary release of labelled vitamin C which will not be observed on the basis of Model 2. In all subjects Model 1 failed to predict the observed plasma concentration profiles for labelled and unlabelled vitamin C, but Model 2 fitted the experimental observations. We speculate on possible physiological explanations for this behaviour, but from the limited information available cannot unequivocally confirm the model structure by identifying the source of the supposed flux.

Type
Research Article
Copyright
Copyright © The Nutrition Society 2005

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