Objectives : Following a re-emergence of iodine deficiency in Australia, mandatory iodine fortification of bread was implemented in October 2009. The objective of the study was to assess the impact of mandatory iodine fortification on the iodine status of populations using the newborn thyroid stimulating hormone (TSH) concentration as a marker.
Methods : The study used an interrupted time series design.TSH data collected between 2005 and 2016 (n=211,033) were extracted from the routine newborn screening program in South Australia for analysis. Iodine deficiency is indicated when more than 3% of newborns have TSH >5 mIU/l. Newborns were classified into three groups: the pre-fortification group (those born before October 2009); the transition group (born between October 2009 and June 2010); and the post-fortification group (born after June 2010). A segmented regression analysis using a Poisson regression model was employed to assess the effect of mandatory iodine fortification on the percentage of newborns with TSH concentration >5 mIU/l.
Results : The percentage of newborns with TSH >5 mIU/l was 5.1%, 6.2% and 4.6% in the pre-fortification, transition and post-fortification groups, respectively. Newborns in the post-fortification period had a 10% lower risk of having TSH >5 mIU/l than newborns in the pre-fortification group [Incidence Rate Ratio (IRR): 0.90; 95% confidence interval (CI): 0.87, 0.94], while newborns in the transitional period had a 22% higher risk of having TSH >5 mIU/l compared with newborns in the pre-fortification period [IRR: 1.22; 95% CI: 1.13, 1.31].
Conclusions : The mandatory iodine fortification decreased the percentage of newborns with TSH >5 mIU/l but iodine status of the population was still classified as mildly deficient using TSH as a marker. Regular monitoring of iodine status using multiple markers of population iodine status is important to evaluate the efficacy and safety of the fortification program.
Funding Sources :
Molla Wassie was supported by The University of Adelaide. Lisa Yelland was supported by an Australian National Health and Medical Research Council Early Career Fellowship.