The rate of intestinal absorption of natural food folates is not related to the extent of folate conjugations

Derek J. McKillop, Helene McNulty, John M. Scott, Joseph M. McPartlin, JJ Strain, Ian Bradbury, Jayne Girvan, Leane Hoey, Richard McCreedy, Joy Alexander, B. Karen Patterson, Mary P.A Hannon-Fletcher, Kristina Pentieva

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32 Citations (Scopus)


Background: Evidence is conflicting as to whether the bioavailability of food folates is influenced by the extent of their conjugation. Objective: The objective was to compare the bioavailability of 3 representative food folate sources with various degrees of glutamylation-ie. egg yolk, spinach, and yeast, whose polyglutamyl folate content measured 0%, 50%, and 100%, respectively. Design: In a randomized crossover trial, 13 male subjects, after a prestudy folate saturation procedure, received in random order either placebo or 500 mu g total folate, which was provided as concentrated freeze-dried extract removed from the normal food matrix of egg yolk, spinach. or yeast. Blood samples (n = 10) were collected before and up to 10 h after treatments, which were administered at weekly intervals. Results: A significant increase from baseline plasma folate concentrations was observed by 0.5 h after treatment with egg yolk folate or spinach folate and by 1 h after treatment with yeast folate, and the concentrations remained significantly elevated for 3-5 h; no plasma folate response was observed after placebo treatment. The overall responses. calculated as plasma folate area under the curve (AUC) for egg yolk, spinach, and yeast folate, were 122.6 +/- 23.6, 136.2 +/- 21.4. and 102.5 +/- 21.1 nmol . h/L, respectively. No significant differences in AUC were seen between monoglutamyl (egg yolk) folate and either of the polyglutamate-containing folates examined. Conclusion: These results suggest that the ratio of monoglutamate to polyglutamate in natural folates is not a factor that limits the extent of intestinal absorption of food folate.
Original languageEnglish
Pages (from-to)167-173
JournalAmerican Journal of Clinical Nutrition
Issue number1
Publication statusPublished (in print/issue) - Jul 2006


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