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

Objective: 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. Design, setting: 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). Participants: 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). Main outcome measure: Median UIC (spot urine samples analysed by a reference laboratory), by Indigenous status, remoteness of residence, and sex. Results: Among the 368 participants assessed both pre- and post-fortification, the median UIC increased from 58 μg/L (interquartile range [IQR], 35-83 μg/L) pre-fortification to 101 μg/L (IQR, 66-163 μg/L) post-fortification (P<0.001). Urban Indigenous (median IUC, 127 μg/L; IQR, 94-203 μg/L) and non-Indigenous adults (117 μg/L; IQR, 65-160 μg/L) were both iodine-replete post-fortification. The median UIC of remote Indigenous residents increased from 53 μg/L (IQR, 28-75 μg/L) to 94 μg/L (IQR, 63-152 μg/L; p<0.001); that is, still mildly iodine-deficient. The pre-fortification median UIC for 22 pregnant women was 48 μg/L (IQR, 36-67 μg/L), the post-fortification median UIC for 24 pregnant women 93 μg/L (IQR, 62-171 μg/L); both values were considerably lower than the recommended minimum of 150 μg/L for pregnant women. Conclusions: 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.