title: Use of the Method of Triads in the Validation of Sodium and Potassium Intake in the Brazilian Longitudinal Study of Adult Health (ELSA-Brasil).
abstract: BACKGROUND
  Biomarkers are a good choice to be used in the validation of food frequency questionnaire due to the independence of their random errors.
  
  
  OBJECTIVE
  To assess the validity of the potassium and sodium intake estimated using the Food Frequency Questionnaire ELSA-Brasil.
  
  
  METHODS
  A subsample of participants in the ELSA-Brasil cohort was included in this study in 2009. Sodium and potassium intake were estimated using three methods: Semi-quantitative food frequency questionnaire, 12-hour nocturnal urinary excretion and three 24-hour food records. Correlation coefficients were calculated between the methods, and the validity coefficient was calculated using the method of triads. The 95% confidence intervals for the validity coefficient were estimated using bootstrap sampling. Exact and adjacent agreement and disagreement of the estimated sodium and potassium intake quintiles were compared among three methods.
  
  
  RESULTS
  The sample consisted of 246 participants, aged 53±8 years, 52% of women. Validity coefficient for sodium were considered weak (рfood frequency questionnaire actual intake = 0.37 and рbiomarker actual intake = 0.21) and moderate (рfood records actual intake 0.56). The validity coefficient were higher for potassium (рfood frequency questionnaire actual intake = 0.60; рbiomarker actual intake = 0.42; рfood records actual intake = 0.79). Conclusions: The Food Frequency Questionnaire ELSA-Brasil showed good validity in estimating potassium intake in epidemiological studies. For sodium validity was weak, likely due to the non-quantification of the added salt to prepared food.
authors.affiliation: Post Graduate Programme in Public Health, Federal University of Espírito Santo, Espírito Santo, Brazil.
authors.forename: Taísa Sabrina Silva
authors.initials: TS
authors.lastname: Pereira
authors.affiliation: Post Graduate Programme in Public Health, Federal University of Espírito Santo, Espírito Santo, Brazil.
authors.forename: Nágela Valadão
authors.initials: NV
authors.lastname: Cade
authors.affiliation: Post Graduate Programme in Public Health, Federal University of Espírito Santo, Espírito Santo, Brazil.
authors.forename: José Geraldo
authors.initials: JG
authors.lastname: Mill
authors.affiliation: Institute of Social Medicine, State University of Rio de Janeiro, Rio de Janeiro, Brazil.
authors.forename: Rosely
authors.initials: R
authors.lastname: Sichieri
authors.affiliation: Post Graduate Programme in Public Health, Federal University of Espírito Santo, Espírito Santo, Brazil.
authors.forename: Maria Del Carmen Bisi
authors.initials: MD
authors.lastname: Molina
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D004034:Diet Surveys / Q000592:standards* / Q000706:statistics & numerical data*; D002149:Energy Intake; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D017419:Potassium, Dietary / Q000008:administration & dosage*; D012982:Sodium, Dietary / Q000008:administration & dosage*; D011795:Surveys and Questionnaires / Q000592:standards*
chemical_list: D017419:Potassium, Dietary; D012982:Sodium, Dietary