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American Journal of Clinical Nutrition, Vol. 84, No. 1, 167-173, July 2006
© 2006 American Society for Nutrition

ORIGINAL RESEARCH COMMUNICATION

The rate of intestinal absorption of natural food folates is not related to the extent of folate conjugation 1,2,3

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 Hannon-Fletcher and Kristina Pentieva

1 From the Northern Ireland Centre for Food and Health, University of Ulster, Coleraine, United Kingdom (DJM, HM, JJS, IB, JG, LH, MH-F, and KP); the Department of Biochemistry, Trinity College, Dublin, Ireland (JMS and JMM); and Loughry College–The Food Centre, Department of Agriculture and Rural Development, Cookstown, United Kingdom (RM, JA, and BKP)

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 µg 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.

Key Words: Food folate • polyglutamylation • plasma folate • folate bioavailability






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