Iodine status in schoolchildren between 1996 and 2003: longitudinal 24-h urinary iodine excretion in 6–12 years old participants of the DONALD study

Abstract

In Germany iodine supply was insufficient in the early nineties, but has improved in the mean time. However, a detailed longitudinal examination of the long-term trend of iodine status, especially the 24-h iodine excretion is lacking so far. Starting in 1996, we repeatedly analysed urinary iodine and sodium excretion in 24-h urine samples (n=1046) of 358 healthy 6–12 years old participants of the DONALD study who regularly used iodized household salt. Energy intake and milk consumption were calculated from dietary records collected in parallel with the urine samples. Median urinary iodine excretion (adjusted for average energy intake of 10–12 years old children (9 MJ/d) increased modestly from 87µg/d to 93µg/d (p=0.003) between 1996 and 1999 and thus lays still below the WHO recommendation of 120µg iodine intake/d for schoolchildren. During the subsequent years, iodine excretion continued to rise (p=0.001) and reached 121µg/d in 2003. Although no comparable trends were observed for milk intake and 24-h sodium excretion, both dietary measures proved to be significant determinants of individual iodine status. The present longitudinal results do not support the recently published findings (also adopted in the WHO Global Database on Iodine Deficiency Disorders) reporting that iodine status in German schoolchildren aged 6–12 years has increased abruptly between the years 1996 and 1999. Despite continuous use of iodized household salt and appropriate consumption of milk products, the median iodine excretion of the DONALD cohort did not meet the WHO reference intake until 2003. It is not yet clear, to what extent increasing iodine densities in certain foods or supplements are responsible for the prolonged positive trend. Irrespective from that, repeated measurements of 24-h iodine excretion in well characterised long-term cohorts, like the DONALD study, may represent a sensitive instrument to monitor relevant trends in iodine status.