title: Vitamin A isotope dilution predicts liver stores in line with long-term vitamin A intake above the current Recommended Dietary Allowance for young adult women.
abstract: BACKGROUND
  The Estimated Average Requirement (EAR) and Recommended Dietary Allowance (RDA) for vitamin A are 1.7 and 2.4 μmol/d (500 and 700 μg retinol activity equivalents/d), respectively, for nonpregnant, nonlactating women aged >19 y. This intake is presumed to maintain a minimally acceptable liver concentration of 0.07 μmol (20 μg) retinol/g; however, liver reserves have not been evaluated with respect to vitamin A intake in women of any age group defined in the Dietary Reference Intakes.
  
  
  OBJECTIVE
  This cross-sectional study examined vitamin A intake and liver reserves estimated by stable-isotope dilution testing.
  
  
  METHODS
  Forty nonpregnant, nonlactating women (mean ± SD age: 22.4 ± 2.3 y) completed a Harvard food-frequency questionnaire (FFQ) and 3-d diet record (3DDR) before undergoing vitamin A status assessment by using a [(13)C2]retinol stable-isotope dilution test.
  
  
  RESULTS
  Vitamin A intake was 70% higher than the RDA by both dietary-assessment methods (P < 0.001). The mean (±SD) liver concentration of vitamin A was 0.45 ± 0.31 μmol/g (129 ± 89 μg/g) and ranged from 0.09 (26 μg/g) to 1.79 μmol/g (513 μg/g). Liver and total-body vitamin A were highly correlated with intake measured by FFQ (P ≤ 0.009), but 3DDR was not (P ≥ 0.22). Prediction equations were developed for 3- and 7-d data.
  
  
  CONCLUSIONS
  In this well-nourished population, vitamin A consumption was considerably higher than recommended, and liver reserves were consistent with intake. Because of their sensitivity, stable-isotope techniques can help to describe the vitamin A status and better characterize the intake needs of all groups defined in the Dietary Reference Intakes. Registration was not required for this trial.
authors.affiliation: Interdepartmental Graduate Program in Nutritional Sciences, Department of Nutritional Sciences, University of Wisconsin, Madison, WI.
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Valentine
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Davis
authors.forename: Sherry A
authors.initials: SA
authors.lastname: Tanumihardjo
mesh_terms: D000328:Adult; D002247:Carbon Isotopes / Q000097:blood; D003430:Cross-Sectional Studies; D015930:Diet Records; D005260:Female; D006801:Humans; D007201:Indicator Dilution Techniques; D008099:Liver / Q000187:drug effects* / Q000378:metabolism; D009751:Nutritional Requirements; D009752:Nutritional Status; D064167:Recommended Dietary Allowances; D011795:Surveys and Questionnaires; D014801:Vitamin A / Q000008:administration & dosage* / Q000097:blood*; D055815:Young Adult
chemical_list: D002247:Carbon Isotopes; D014801:Vitamin A
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