Volume 91, Issue 5, May (2004), pp. 699-705 © The Author 2004
doi:10.1079/BJN20041103

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Stable isotope-labelled vitamin C as a probe for vitamin C absorption by human subjects

Christopher J. Bates¹, Kerry S. Jones¹ and Leslie J. C. Bluck^1
1MRC Human Nutrition Research, Cambridge, UK

 (Received 8 September 2003–Revised 15 January 2004–Accepted 22 January 2004)

Factors affecting absorption of physiological doses of vitamin C in man have not been widely studied, partly because few suitable tools exist to distinguish recently absorbed vitamin C from endogenous vitamin. Stable isotope-labelled vitamin C provides such a tool. Fifteen healthy non-smoking subjects aged 26–59 years were studied. Each received 30mg l-[1-¹³C]ascorbic acid orally on two occasions, 3–4 weeks apart. The ascorbate was given alone or with Fe (100mg as ferrous fumarate) or with red grape juice, which is rich in polyphenols. Blood was collected at frequent intervals for 1h, and then each hour for a further 3h. Total concentration of vitamin C was measured fluorometrically and its ¹³C-isotope enrichment was measured by GC–MS after conversion to volatile trimethylsilyl esters. Peak plasma enrichment occurred within 25–50min. No kinetic variables were significantly altered by the iron fumarate supplement. Grape juice attenuated vitamin C absorption, reaching significance at the 20min time point. There were weak correlations between isotope enrichment and body weight or endogenous ascorbate concentration. The increment in total plasma ascorbate was smaller if calculated from isotope enrichment than from vitamin C concentration increase. The dilution pool was much larger than the plasma ascorbate pool. Further studies are needed to resolve these paradoxes. Stable isotope-labelled ascorbate is potentially useful for measurement of vitamin C absorption by human subjects.

Keywords:
Vitamin C, Ascorbate, Absorption, Stable isotope, Human subjects

Abbreviations:
AUC, area under the curve