title: Using 2 Assessment Methods May Better Describe Dietary Supplement Intakes in the United States.
abstract: BACKGROUND
  One-half of US adults report using a dietary supplement. NHANES has traditionally assessed dietary supplement use via a 30-d questionnaire but in 2007 added a supplement module to the 24-h dietary recall (24HR).
  
  
  OBJECTIVE
  We compared these 2 dietary assessment methods, examined potential biases in the methods, and determined the effect that instrument choice had on estimates of prevalence of multivitamin/multimineral dietary supplement (MVMM) use.
  
  
  METHODS
  We described prevalence of dietary supplement use by age, sex, and assessment instrument in 12,285 adults in the United States (>19 y of age) from NHANES 2007-2010.
  
  
  RESULTS
  When using data from the questionnaire alone, 29.3% ± 1.0% of men and 35.5% ± 1.0% of women were users of MVMMs, whereas data from the 24HR only produced prevalence estimates of 26.3% ± 1.1% for men and 33.2% ± 1.0% for women. When using data from both instruments combined, 32.3% ± 1.2% of men and 39.5% ± 1.1% of women were classified as MVMM users. Prevalence estimates were significantly higher by 2-9% in all age-sex groups when using information from both instruments combined than when using data from either instrument individually. A digit preference bias and flattened slope phenomenon were observed in responses to the dietary supplement questionnaire. A majority (67%) of MVMMs were captured on both instruments, whereas 19% additional MVMMs were captured on the questionnaire and 14% additional on the 24HR. Of those captured only on the 24HR, 26% had missing label information, whereas only 12% and 9% of those captured on the questionnaire or both, respectively, had missing information.
  
  
  CONCLUSIONS
  Use of both the dietary supplement questionnaire and the 24HR can provide advantages to researchers over the use of a single instrument and potentially capture a larger fraction of dietary supplement users.
authors.affiliation: Division of Cardiovascular Sciences, National Heart, Lung, and Blood Institute, holly.nicastro@nih.gov.
authors.forename: Holly L
authors.initials: HL
authors.lastname: Nicastro
authors.affiliation: Office of Dietary Supplements, Office of the Director, and.
authors.forename: Regan L
authors.initials: RL
authors.lastname: Bailey
authors.affiliation: Division of Cancer Prevention, National Cancer Institute, NIH, Bethesda, MD.
authors.forename: Kevin W
authors.initials: KW
authors.lastname: Dodd
mesh_terms: D000328:Adult; D000368:Aged; D003430:Cross-Sectional Studies; D019587:Dietary Supplements / Q000706:statistics & numerical data*; D005260:Female; D006801:Humans; D008297:Male; D011939:Mental Recall; D018977:Micronutrients / Q000008:administration & dosage*; D008875:Middle Aged; D015596:Nutrition Assessment; D009749:Nutrition Surveys; D011795:Surveys and Questionnaires; D014481:United States; D055815:Young Adult
chemical_list: D018977:Micronutrients
keywords: NHANES; dietary assessment; dietary supplement; measurement error; multivitamin multimineral