Iodine status of Indigenous and non-Indigenous young adults in the Top End, before and after mandatory fortification.

Abstract

To assess the median urine iodine concentration (UIC) of young adults in the Top End of Northern Territory, before and after fortification of bread with iodised salt became mandatory. Analysis of cross-sectional data from two longitudinal studies, the Aboriginal Birth Cohort and the non-Indigenous Top End Cohort, pre- (Indigenous participants: 2006-2007; non-Indigenous participants: 2007-2009) and post-fortification (2013-15). Indigenous and non-Indigenous Australian young adults (mean age: pre-fortification, 17.9 years (standard deviation [SD], 1.20 years); post-fortification, 24.9 years (SD, 1.34 years). Median UIC (spot urine samples analysed by a reference laboratory), by Indigenous status, remoteness of residence, and sex. Among the 368 participants assessed both pre- and post-fortification, the median UIC increased from 58μg/L (interquartile range [IQR], 35-83μg/L) pre-fortification to 101μg/L (IQR, 66-163μg/L) post-fortification (P<0.001). Urban Indigenous (median IUC, 127μg/L; IQR, 94-203μg/L) and non-Indigenous adults (117μg/L; IQR, 65-160μg/L) were both iodine-replete post-fortification. The median UIC of remote Indigenous residents increased from 53μg/L (IQR, 28-75μg/L) to 94μg/L (IQR, 63-152μg/L; p<0.001); that is, still mildly iodine-deficient. The pre-fortification median UIC for 22 pregnant women was 48μg/L (IQR, 36-67μg/L), the post-fortification median UIC for 24 pregnant women 93μg/L (IQR, 62-171μg/L); both values were considerably lower than the recommended minimum of 150μg/L for pregnant women. The median UIC of young NT adults increased following mandatory fortification of bread with iodised salt. The median UIC of pregnant Indigenous women in remote locations, however, remains low, and targeted interventions are needed to ensure healthy fetal development.