Stable iodine intake and thyroid screening outcomes after the Fukushima Nuclear Disaster: an observational study.

Abstract

Context: Stable iodine intake is crucial in preventing thyroid cancer after radiological emergencies; however, the association between stable iodine intake and thyroid outcomes in children after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident remains unclear.

Objective: To describe thyroid screening outcomes and investigate the association between stable iodine intake and those outcomes in children after the FDNPP accident.

Design: Observational study.

Setting: Regional thyroid screening program conducted by the Research Institute of Radiation Safety for Disaster Recovery Support in Fukushima, Japan.

Participants: Children born between April 1998 and March 2011 in Miharu Town (n=1,974), where stable iodine intake was implemented during the FDNPP accident.

Intervention: None.

Main outcome measure: The association between stable iodine intake and thyroid ultrasound results was examined using logistic regression analysis. Coarsened exact matching was used to balance sex and age.

Results: Among the participants, 1,095 (55.5%) consumed stable iodine, whereas 879 (44.5%) did not. In the age- and sex-matched group of 1,952 children (1,088 in the intake and 864 in non-intake group), no association was observed between stable iodine intake and thyroid screening results, indicating the need for a detailed examination (odds ratio: 0.839; 95% confidence interval: 0.393─1.8, p = 0.647). The volume and parenchymal heterogeneity were not different between these groups.

Conclusions: Stable iodine intake was not associated with thyroid ultrasound screening results, probably because of the low radiation doses following the FDNPP accident. Parenchymal heterogeneity and thyroid volume were similar, supporting the conclusion that the adverse effects of single-dose stable iodine are minimal.