Iodine status of Aboriginal teenagers in the Darwin region before mandatory iodine fortification of bread

Objective: To determine the iodine status of participants in the Aboriginal Birth Cohort Study who resided in the Darwin Health Region (DHR) in the "Top End" of the Northern Territory prior to the introduction of mandatory iodine fortification of bread. Design, setting and participants: Participants in our study had been recruited at birth and were followed up at a mean age of 17.8 years. Spot urine samples were collected and assessed for iodine concentration at a reference laboratory. The median urinary iodine concentration (MUIC) of residents of the DHR was calculated and compared with international criteria for iodine status. Analyses were conducted for subgroups living in urban areas (Darwin-Palmerston) and remote communities (rural with an Aboriginal council). We collected a repeat sample in a subset of participants to explore the impact of within-person variation on the results. Main outcome measure: MUIC for residents of the DHR. Results: Urine specimens were provided by 376 participants in the DHR. Overall MUIC was 58 mu g/L when weighted to the 2006 Census population. Urban boys had higher values (MUIC = 77 mu g/L) than urban and remote-dwelling non-pregnant girls (MUIC = 55 mu g/L), but all these groups were classified as mildly iodine deficient. Remote-dwelling boys had the lowest MUIC (47 mu g/L, moderate deficiency). Pregnant girls and those with infants aged less than 6 months also had insufficient iodine status. Correction for within-person variation reduced the spread of the population distribution. Conclusions: Previously, iodine deficiency was thought to occur only in the southeastern states of Australia. This is the first report of iodine deficiency occurring in residents of the NT. It is also the first study of iodine status in a defined Indigenous population. Future follow-up will reassess iodine status in this group after the introduction of iodine fortification of bread.