title: Use of a short-term isotope-dilution method for determining the vitamin A status of children.
abstract: BACKGROUND
  After a dose of labeled vitamin A is given to humans for estimating body stores of vitamin A, blood is customarily drawn at pseudo-equilibration times ranging from 11 to 26 d.
  
  
  OBJECTIVE
  The objective was to determine whether a shorter sample collection interval (6 h or 3 d), which would be more realistic in field settings, can be used.
  
  
  METHODS
  Correlations of enrichment at 6 h or 3 d with enrichment at 21 d were made after an oral dose of deuterium-labeled vitamin A was given to Chinese schoolchildren (aged 10-11 y; n = 58) with marginal-to-normal vitamin A status. A predictive equation was then derived and applied to data obtained from a separate group of children to verify that the calculated enrichment at 21 d (determined by using data obtained at an earlier time point to predict 21-d enrichment) reflected directly measured enrichment at 21 d.
  
  
  RESULTS
  Because 3-d isotope enrichment was found to correlate well with 21-d enrichment, a predictive equation was derived whereby 3-d data were used to predict isotope enrichment at pseudo-equilibration (ie, at 21 d). When the 3-d predictive equation was applied to a separate group of Chinese children, the calculated 21-d data (determined by using the 3-d data and the predictive equation) matched the directly measured 21-d data. Body stores of vitamin A determined from either the calculated or directly measured 21-d enrichment data also showed agreement.
  
  
  CONCLUSIONS
  Percentage enrichment at 3 d (but not at 6 h) can be used to evaluate vitamin A body stores in humans.
authors.affiliation: Jean Mayer US Department of Agriculture Human Nutrition Research Center on Aging at Tufts University, Boston, MA 02111, USA. gtang@hnrc.tufts.edu
authors.forename: Guangwen
authors.initials: G
authors.lastname: Tang
authors.forename: Jian
authors.initials: J
authors.lastname: Qin
authors.forename: Lan-ying
authors.initials: LY
authors.lastname: Hao
authors.forename: Shi-an
authors.initials: SA
authors.lastname: Yin
authors.forename: Robert M
authors.initials: RM
authors.lastname: Russell
mesh_terms: D002648:Child; D002681:China; D002851:Chromatography, High Pressure Liquid; D004032:Diet; D005260:Female; D006801:Humans; D007553:Isotope Labeling; D008297:Male; D009752:Nutritional Status; D011237:Predictive Value of Tests; D013997:Time Factors; D014801:Vitamin A / Q000008:administration & dosage / Q000097:blood*
chemical_list: D014801:Vitamin A