title: Validation of a food frequency questionnaire to determine vitamin D intakes using the method of triads.
abstract: BACKGROUND
  Dietary sources of vitamin D (both natural and fortified) are increasingly contributing to consumers' vitamin D intake and status. Therefore, the present study aimed to validate a vitamin D food frequency questionnaire (FFQ) for the assessment of habitual vitamin D intake.
  
  
  METHODS
  A total of 49 apparently healthy consenting adults (aged 18-64 years) from the local community were sampled at the end of winter. Dietary intakes were recorded using a 4-day weighed food record (4d-WFR) and a 17-item FFQ based on foods known to contribute to dietary vitamin D intake. Fasting vitamin D status was quantified by serum 25-hydroxyvitamin D [25(OH)D] using liquid chromatography tandem mass spectrometry. The method of triads was applied using these three measurements to determine the overall validity of the FFQ.
  
  
  RESULTS
  Vitamin D intakes from 4d-WFR ranged between 0.42 and 31.65 μg day(-1), whereas intakes determined from the FFQ ranged from 1.03 to 36.08 μg day(-1). Serum 25(OH)D concentrations ranged between 12.89 and 279.00 nmol L(-1). The mean (SD) difference between the FFQ and 4d-WFR was +1.62 ( 3.86). There were strong correlations between the vitamin D intake estimated by the FFQ and that from the 4d-WFR (r = 0.562) and also with serum 25(OH)D concentrations (r = 0.567). Vitamin D intake estimated from the 4d-WFR was also strongly correlated with serum 25(OH)D concentrations (r = 0.411). The overall validity coefficient calculated using the method of triads was high (0.881).
  
  
  CONCLUSIONS
  The vitamin D FFQ has been validated for use in future studies aiming to assess habitual vitamin D intake.
authors.affiliation: Northern Ireland Centre for Food and Health (NICHE), University of Ulster, Coleraine, UK.
authors.forename: R R
authors.initials: RR
authors.lastname: Weir
authors.affiliation: Northern Ireland Centre for Food and Health (NICHE), University of Ulster, Coleraine, UK.
authors.forename: E L
authors.initials: EL
authors.lastname: Carson
authors.affiliation: Northern Ireland Centre for Food and Health (NICHE), University of Ulster, Coleraine, UK.
authors.forename: M S
authors.initials: MS
authors.lastname: Mulhern
authors.affiliation: Institute of Molecular Medicine, School of Medicine, Trinity College, Dublin, Ireland.
authors.forename: E
authors.initials: E
authors.lastname: Laird
authors.affiliation: The Department of Clinical Biochemistry, St James's Hospital, Dublin, Ireland.
authors.forename: M
authors.initials: M
authors.lastname: Healy
authors.affiliation: Northern Ireland Centre for Food and Health (NICHE), University of Ulster, Coleraine, UK.
authors.forename: L K
authors.initials: LK
authors.lastname: Pourshahidi
mesh_terms: D000293:Adolescent; D000328:Adult; D015415:Biomarkers / Q000097:blood; D002853:Chromatography, Liquid; D004032:Diet; D015930:Diet Records; D002149:Energy Intake; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D009752:Nutritional Status; D015203:Reproducibility of Results; D018401:Sample Size; D012621:Seasons; D011795:Surveys and Questionnaires; D053719:Tandem Mass Spectrometry; D014807:Vitamin D / Q000008:administration & dosage* / Q000097:blood; D055815:Young Adult
chemical_list: D015415:Biomarkers; D014807:Vitamin D
keywords: food frequency questionnaire; method of triads; triangulation; validation; vitamin D