title: Variability of the conversion of beta-carotene to vitamin A in women measured by using a double-tracer study design.
abstract: BACKGROUND
  Blood beta-carotene and vitamin A responses to oral beta-carotene are variable in humans. Some individuals are characterized as responders and others as low- or nonresponders. A better understanding of the conditions that produce the variability is important to help design public health programs that ensure vitamin A sufficiency.
  
  
  OBJECTIVE
  Our objective was to assess variability in absorption and conversion of beta-carotene to vitamin A in vivo in humans by using a novel double-tracer ¿hexadeuterated (D(6)) beta-carotene and D(6) retinyl acetate approach.
  
  
  METHODS
  Eleven healthy women were housed at the US Department of Agriculture Western Human Nutrition Research Center metabolic unit for 44 d, where they consumed diets adequate in vitamins and minerals except for carotenoids. After an adaptation period, the women were given 30 micromol D(6) retinyl acetate orally, followed 1 wk later with 37 micromol D(6) beta-carotene (approximately equimolar doses). Time-dependent plasma concentration curves were determined for D(6) retinol, D(6) beta-carotene, and trideuterated (D(3)) retinol (derived from D(6) beta-carotene).
  
  
  RESULTS
  Mean (+/-SE) absorption of D(6) beta-carotene was 3.3 +/- 1.3% for all subjects. The mean conversion ratio was 0.81 +/- 0.34 mol D(3) retinol to 1 mol D(6) beta-carotene for all subjects. However, only 6 of the 11 subjects had plasma D(6) beta-carotene and D(3) retinol concentrations that we could measure. The mean absorption of D(6) beta-carotene in these 6 subjects was 6.1 +/- 0.02% and their conversion ratio was 1.47 +/- 0.49 mol D(3) retinol to 1 mol D(6) beta-carotene. The remaining 5 subjects were low responders with </=0.01% absorption and a mean conversion ratio of 0.014 +/- 0.004 mol D(3) retinol to 1 mol D(6) beta-carotene.
  
  
  CONCLUSIONS
  Variable absorption and conversion of beta-carotene to vitamin A both contribute to the variable response to consumption of beta-carotene. Our double-tracer approach is adaptable for identifying efficient converters of carotenoid to retinoid.
authors.affiliation: Department of Nutrition, University of California, Davis, CA 95616, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Lin
authors.forename: S R
authors.initials: SR
authors.lastname: Dueker
authors.forename: B J
authors.initials: BJ
authors.lastname: Burri
authors.forename: T R
authors.initials: TR
authors.lastname: Neidlinger
authors.forename: A J
authors.initials: AJ
authors.lastname: Clifford
mesh_terms: D000042:Absorption; D000328:Adult; D001682:Biological Availability; D003903:Deuterium; D004224:Diterpenes; D005260:Female; D006801:Humans; D007700:Kinetics; D000084562:Retinyl Esters; D014801:Vitamin A / Q000031:analogs & derivatives / Q000097:blood*; D019207:beta Carotene / Q000008:administration & dosage* / Q000097:blood / Q000493:pharmacokinetics*
chemical_list: D004224:Diterpenes; D000084562:Retinyl Esters; D019207:beta Carotene; D014801:Vitamin A; C009166:retinol acetate; D003903:Deuterium