title: Examination of iodine status in the German population: an example for methodological pitfalls of the current approach of iodine status assessment.
abstract: OBJECTIVE
  Preliminary iodine concentration (UIC) measurements in spot urines of the representative German adult study DEGS indicated a severe worsening of iodine status compared to previous results in German children (KiGGS study). Therefore, we aimed to evaluate adult iodine status in detail and to investigate the impact of hydration status on UIC.
  
  
  METHODS
  UIC and creatinine concentrations were measured in 6978 spot urines from the German nationwide DEGS study (2008-2011). Twenty-four-hour iodine excretions (24-h UIE) were estimated by relating iodine/creatinine ratios to age- and sex-specific 24-h creatinine reference values. Urine osmolality was measured in two subsamples of spot urines (n = 100 each) to determine the impact of hydration status on UIC.
  
  
  RESULTS
  In DEGS, median UIC was 69 µg/L in men and 54 µg/L in women, lying clearly below the WHO cutoff for iodine sufficiency (100 µg/L). Estimated median 24-h UIE was 113 µg/day, accompanied by 32 % of DEGS adults, lying below the estimated average requirement (EAR) for iodine. Comparative analysis with the KiGGS data (>14,000 spot urines of children; median UIC 117 µg/L) revealed a comparable percentage <EAR (33 %). In two DEGS subsamples with significantly different UIC but similar median 24-h UIE, osmolality was twofold higher in the high- versus the low-UIC group.
  
  
  CONCLUSIONS
  Over 30 % of participants in the two German surveys had an estimated iodine intake less than the respective age-group-specific EAR. Our data strongly suggest that even in large surveys, hydration status can considerably interfere with the epidemiological iodine assessment parameter UIC. The present data can serve as an example how to evaluate population-based spot urine data on a 24-h basis, independent of hydration status.
authors.affiliation: IEL-Nutritional Epidemiology, DONALD Study Centre at the Research Institute of Child Nutrition, University of Bonn, Dortmund, Germany.
authors.forename: S A
authors.initials: SA
authors.lastname: Johner
authors.affiliation: Central Epidemiology Laboratory, Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Thamm
authors.affiliation: Health of Children and Adolescents, Prevention Concepts, Department of Epidemiology and Health Monitoring, Robert Koch Institute, Berlin, Germany.
authors.forename: R
authors.initials: R
authors.lastname: Schmitz
authors.affiliation: IEL-Nutritional Epidemiology, DONALD Study Centre at the Research Institute of Child Nutrition, University of Bonn, Dortmund, Germany. remer@uni-bonn.de.
authors.forename: T
authors.initials: T
authors.lastname: Remer
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D003404:Creatinine / Q000652:urine; D003430:Cross-Sectional Studies; D005260:Female; D005858:Germany; D006801:Humans; D007455:Iodine / Q000652:urine*; D008137:Longitudinal Studies; D008297:Male; D008875:Middle Aged; D015596:Nutrition Assessment; D009752:Nutritional Status; D009994:Osmolar Concentration; D012016:Reference Values; D055815:Young Adult
chemical_list: D007455:Iodine; D003404:Creatinine
keywords: 24-h Iodine excretion; Creatinine; DEGS study; Iodine; Spot urine