title: Plasma concentration of folate as a biomarker for the intake of fruit and vegetables: the Hordaland Homocysteine Study.
abstract: BACKGROUND
  Nutritional biomarkers may be used to assess dietary exposure without the errors commonly associated with self-reported dietary data.
  
  
  OBJECTIVE
  The objective was to examine the association between plasma folate and intake of folate, fruit, and vegetables in a large cohort of healthy adults consuming foods that had not been fortified with folic acid.
  
  
  METHODS
  The present study population included 5533 middle-aged (47-49 y) and old (71-74 y) subjects from the Hordaland Homocysteine Study. The participants completed a food-frequency questionnaire and provided blood samples for chemical analyses.
  
  
  RESULTS
  We observed a significant difference in plasma concentrations of folate across increasing quartiles of fruit, vegetable, and orange juice consumption. The difference in plasma folate between the highest and lowest quartiles was 1.97 (95% CI: 1.86, 2.07) nmol/L for fruit intake, 1.79 (95% CI: 1.69, 1.89) nmol/L for vegetable intake, and 2.69 (95% CI: 2.51, 2.87) nmol/L for orange juice intake. A significant inverse relation was observed across increasing quartiles of milk and bread intakes. The difference between the highest and lowest quartiles was -1.03 (95% CI: -1.13, -0.92) nmol/L for milk and -1.60 (95% CI: -1.69, -1.50) nmol/L for bread.
  
  
  CONCLUSIONS
  Plasma folate concentration may be a useful biomarker for the intake of fruit and vegetables in populations consuming unfortified food products. The association can be attenuated by and should be corrected for individual intake of folic acid supplements.
authors.affiliation: Department of Nutrition, School of Medicine, University of Oslo, Oslo, Norway. asgeir.brevik@medisin.uio.no
authors.forename: Asgeir
authors.initials: A
authors.lastname: Brevik
authors.forename: Stein Emil
authors.initials: SE
authors.lastname: Vollset
authors.forename: Grethe S
authors.initials: GS
authors.lastname: Tell
authors.forename: Helga
authors.initials: H
authors.lastname: Refsum
authors.forename: Per Magne
authors.initials: PM
authors.lastname: Ueland
authors.forename: Elin Bjorge
authors.initials: EB
authors.lastname: Loeken
authors.forename: Christian A
authors.initials: CA
authors.lastname: Drevon
authors.forename: Lene Frost
authors.initials: LF
authors.lastname: Andersen
mesh_terms: D000368:Aged; D000704:Analysis of Variance; D000818:Animals; D015415:Biomarkers / Q000097:blood; D001939:Bread / Q000009:adverse effects; D015331:Cohort Studies; D004034:Diet Surveys; D019587:Dietary Supplements; D005260:Female; D005492:Folic Acid / Q000008:administration & dosage / Q000097:blood*; D005638:Fruit; D006710:Homocysteine / Q000097:blood*; D006801:Humans; D008297:Male; D008875:Middle Aged; D008892:Milk / Q000009:adverse effects; D015596:Nutrition Assessment; D011795:Surveys and Questionnaires; D014675:Vegetables
chemical_list: D015415:Biomarkers; D006710:Homocysteine; D005492:Folic Acid