title: The absorption of iron from whole diets: a systematic review.
abstract: BACKGROUND
  Absorption factors are required to convert physiologic requirements for iron into Dietary Reference Values, but the absorption from single meals cannot be used to estimate dietary iron absorption.
  
  
  OBJECTIVE
  The objective was to conduct a systematic review of iron absorption from whole diets.
  
  
  METHODS
  A structured search was completed by using the Medline, EMBASE, and Cochrane CENTRAL databases from inception to November 2011. Formal inclusion and exclusion criteria were applied, and data extraction, validity assessment, and meta-analyses were undertaken.
  
  
  RESULTS
  Nineteen studies from the United States, Europe, and Mexico were included. Absorption from diets was higher with an enhancer (standard mean difference: 0.53; 95% CI: 0.21, 0.85; P = 0.001) and was also higher when compared with low-bioavailability diets (standard mean difference: 0.96; 95% CI: 0.51, 1.41; P < 0.0001); however, single inhibitors did not reduce absorption (possibly because of the limited number of studies and participants and their heterogeneity). A regression equation to calculate iron absorption was derived by pooling data for iron status (serum and plasma ferritin) and dietary enhancers and inhibitors from 58 individuals (all from US studies): log[nonheme-iron absorption, %] = -0.73 log[ferritin, μg/L] + 0.11 [modifier] + 1.82. In individuals with serum ferritin concentrations from 6 to 80 μg/L, predicted absorption ranged from 2.1% to 23.0%.
  
  
  CONCLUSIONS
  Large variations were observed in mean nonheme-iron absorption (0.7-22.9%) between studies, which depended on iron status (diet had a greater effect at low serum and plasma ferritin concentrations) and dietary enhancers and inhibitors. Iron absorption was predicted from serum ferritin concentrations and dietary modifiers by using a regression equation. Extrapolation of these findings to developing countries and to men and women of different ages will require additional high-quality controlled trials.
authors.affiliation: Norwich Medical School, University of East Anglia, Norwich Research Park, Norwich, United Kingdom.
authors.forename: Rachel
authors.initials: R
authors.lastname: Collings
authors.forename: Linda J
authors.initials: LJ
authors.lastname: Harvey
authors.forename: Lee
authors.initials: L
authors.lastname: Hooper
authors.forename: Rachel
authors.initials: R
authors.lastname: Hurst
authors.forename: Tracey J
authors.initials: TJ
authors.lastname: Brown
authors.forename: Jennifer
authors.initials: J
authors.lastname: Ansett
authors.forename: Maria
authors.initials: M
authors.lastname: King
authors.forename: Susan J
authors.initials: SJ
authors.lastname: Fairweather-Tait
mesh_terms: D000042:Absorption; D001682:Biological Availability; D004032:Diet; D005060:Europe; D005293:Ferritins / Q000097:blood; D006801:Humans; D019266:Iron, Dietary / Q000008:administration & dosage* / Q000097:blood* / Q000493:pharmacokinetics*; D008800:Mexico; D014481:United States
chemical_list: D019266:Iron, Dietary; D005293:Ferritins