title: The rate of intestinal absorption of natural food folates is not related to the extent of folate conjugation.
abstract: 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.
  
  
  METHODS
  In a randomized crossover trial, 13 male subjects, after a prestudy folate saturation procedure, received in random order either placebo or 500 mug 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.
  
  
  CONCLUSIONS
  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.
authors.affiliation: Northern Ireland Centre for Food and Health, University of Ulster, Coleraine, United Kingdom.
authors.forename: Derek J
authors.initials: DJ
authors.lastname: McKillop
authors.forename: Helene
authors.initials: H
authors.lastname: McNulty
authors.forename: John M
authors.initials: JM
authors.lastname: Scott
authors.forename: Joseph M
authors.initials: JM
authors.lastname: McPartlin
authors.forename: J J
authors.initials: JJ
authors.lastname: Strain
authors.forename: Ian
authors.initials: I
authors.lastname: Bradbury
authors.forename: Jayne
authors.initials: J
authors.lastname: Girvan
authors.forename: Leane
authors.initials: L
authors.lastname: Hoey
authors.forename: Richard
authors.initials: R
authors.lastname: McCreedy
authors.forename: Joy
authors.initials: J
authors.lastname: Alexander
authors.forename: B Karen
authors.initials: BK
authors.lastname: Patterson
authors.forename: Mary
authors.initials: M
authors.lastname: Hannon-Fletcher
authors.forename: Kristina
authors.initials: K
authors.lastname: Pentieva
mesh_terms: D000284:Administration, Oral; D000328:Adult; D019540:Area Under Curve; D001682:Biological Availability; D018592:Cross-Over Studies; D004311:Double-Blind Method; D004530:Egg Yolk / Q000737:chemistry*; D005492:Folic Acid / Q000008:administration & dosage / Q000097:blood / Q000737:chemistry / Q000493:pharmacokinetics*; D006801:Humans; D007408:Intestinal Absorption; D008297:Male; D018724:Spinacia oleracea / Q000737:chemistry*; D015003:Yeasts
chemical_list: D005492:Folic Acid