title: Variation in the iodine concentrations of foods: considerations for dietary assessment.
abstract: BACKGROUND
  Food-composition tables typically give measured nutrient concentrations in foods as a single summary value, often the mean, without providing information as to the shape of the distribution.
  
  
  OBJECTIVE
  Our objective was to explore how the statistical approach chosen to describe the iodine concentrations of foods affects the proportion of the population identified as having either insufficient or excessive iodine intakes.
  
  
  METHODS
  We used food intake data reported by the 2009-2010 NHANES and measured iodine concentrations of Total Diet Study (TDS) foods from 4 US regions sampled in 2004-2011. We created 4 data sets, each by using a different summary statistic (median, mean, and 10th and 90th percentiles), to represent the iodine concentration distribution of each TDS food. We estimated the iodine concentration distribution of each food consumed by NHANES participants as the 4 iodine concentration summary statistics of a similar TDS food and used these, along with NHANES food intake data, to develop 4 estimates of each participant's iodine intake on each survey day. Using the 4 estimates in turn, we calculated 4 usual iodine intakes for each sex- and age-specific subgroup. We then compared these to guideline values and developed 4 estimates of the proportions of each subgroup with deficient and excessive usual iodine intakes.
  
  
  RESULTS
  In general, the distribution of iodine intakes was poorly characterized when food iodine concentrations were expressed as mean values. In addition, mean values predicted lower prevalences of iodine deficiency than did median values. For example, in women aged 19-50 y, the estimated prevalence of iodine deficiency was 25% when based on median food iodine concentrations but only 5.8% when based on mean values.
  
  
  CONCLUSIONS
  For nutrients such as iodine with highly variable concentrations in important food sources, we recommend that food-composition tables provide useful variability information, including the mean, SD, and median.
authors.affiliation: Department of Statistics, Iowa State University, Ames, IA; alicia@iastate.edu.
authors.forename: Alicia L
authors.initials: AL
authors.lastname: Carriquiry
authors.affiliation: US Food and Drug Administration, College Park, MD;
authors.forename: Judith H
authors.initials: JH
authors.lastname: Spungen
authors.affiliation: University of Hawaii Cancer Center, Honolulu, HI;
authors.forename: Suzanne P
authors.initials: SP
authors.lastname: Murphy
authors.affiliation: Nutrient Data Laboratory, Beltsville Human Nutrition Research Center, Agricultural Research Service, USDA, Beltsville, MD; and.
authors.forename: Pamela R
authors.initials: PR
authors.lastname: Pehrsson
authors.affiliation: Office of Dietary Supplements, NIH, Bethesda, MD.
authors.forename: Johanna T
authors.initials: JT
authors.lastname: Dwyer
authors.affiliation: US Food and Drug Administration, College Park, MD;
authors.forename: WenYen
authors.initials: W
authors.lastname: Juan
authors.affiliation: US Food and Drug Administration, College Park, MD;
authors.forename: Mark S
authors.initials: MS
authors.lastname: Wirtz
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D002648:Child; D002675:Child, Preschool; D066264:Datasets as Topic / Q000706:statistics & numerical data; D004032:Diet; D005247:Feeding Behavior; D005260:Female; D005502:Food; D006801:Humans; D007223:Infant; D007454:Iodides / Q000008:administration & dosage; D007455:Iodine / Q000008:administration & dosage* / Q000172:deficiency; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D018673:Nutrition Policy; D009749:Nutrition Surveys; D009751:Nutritional Requirements; D044343:Overnutrition; D012107:Research Design / Q000706:statistics & numerical data; D014481:United States; D055815:Young Adult
chemical_list: D007454:Iodides; D007455:Iodine
keywords: food composition; iodine; nutrient content; statistical distribution; variability