Examination of iodine status in the German population: an example for methodological pitfalls of the current approach of iodine status assessment

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. 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. In DEGS, median UIC was 69 A mu g/L in men and 54 A mu g/L in women, lying clearly below the WHO cutoff for iodine sufficiency (100 A mu g/L). Estimated median 24-h UIE was 113 A mu g/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 A mu g/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. 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.