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

Abstract

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 30 mg L-[1-13 C]ascorbic acid orally on two occasions, 3 -4 weeks apart. The ascorbate was given alone or with Fe (100 mg as ferrous fumarate) or with red grape juice, which is rich in polyphenols. Blood was collected at frequent intervals for 1 h, and then each hour for a further 3 h. Total concentration of vitamin C was measured fluorometrically and its 13 C-isotope enrichment was measured by GC -MS after conversion to volatile trimethylsilyl esters. Peak plasma enrichment occurred within 25 -50 min. No kinetic variables were significantly altered by the iron fumarate supplement. Grape juice attenuated vitamin C absorption, reaching significance at the 20 min 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.

Supplementation of a γ-tocopherol-rich mixture of tocopherols in healthy men protects against vascular endothelial dysfunction induced by postprandial hyperglycemia

“…Co-supplementation of vitamin C and vitamin E immediately prior to an oral glucose challenge prevented the decrease in postprandial FMD responses that otherwise occurred with hyperglycemia [6]. However, maximal plasma vitamin E occurs~10 h following ingestion [32], whereas maximal plasma vitamin C occurs~60 min postingestion [33]. Thus, the maintenance of VEF following glucose ingestion in combination with supplementation of vitamins C and E [6] most likely reflects improvements in vitamin C status rather than vitamin E. Thus, our study provides the first direct evidence that dietary vitamin E supplementation, provided as γ-TmT, attenuates hyperglycemia-mediated impairments in VEF in healthy young men, at least partly by reducing lipid peroxidation.…”

Absorption and Excretion of Ascorbic Acid Alone and in Acerola (Malpighia emarginata) Juice: Comparison in Healthy Japanese Subjects

“…Bates et al 19) also investigated this issue by using stable isotope-labeled ascorbic acid. There, grape juice containing anthocyanins, flavanols and flavonols tended to reduce absorption compared with ascorbic acid alone.…”

Recent progress in stable isotope methods for assessing vitamin metabolism

“…The only relatively recent investigation looked at the interactions between grape juice and iron on vitamin C [56]. The complementary interaction, that is the enhancement of iron absorption by dietary vitamin C has recently been demonstrated [57].…”