Stable Iodine Distribution Among Children After the 2011 Fukushima Nuclear Disaster in Japan: An Observational Study

Abstract Context Intake of stable iodine helps prevent childhood thyroid cancer in nuclear emergencies, but there is limited case information. Objective We identified the intake rate and the factors associated with no intake among children who did not take stable iodine after the Fukushima disaster. Design Retrospective observational study. Setting Data were obtained from thyroid cancer screenings performed from August through November 2017. Participants Children in Miharu Town, Fukushima, Japan. Intervention No intervention. Main Outcome Measures We performed multilevel logistic regression analysis at the regional and individual levels. We qualitatively examined the reasons for no intake of stable iodine based on closed- and open-ended questions. Results The rate of distribution was 94.9%, but the intake rate was only 63.5%. Intake was lower in those aged 0 to 2 years compared with those aged ≥3 years (OR, 0.21; 95% CI, 0.11 to 0.36). Parents’ intake was positively associated with their children’s intake (OR, 61.0; 95% CI, 37.9 to 102.9). The variance partition coefficient for regions was 0.021, suggesting that the intake of stable iodine was more likely affected by individual than by regional factors. Closed-ended questions showed that the main reason for avoiding intake was concern about safety. Open-ended questions for other reasons revealed issues related to the distribution method, information about the effects and adverse effects of iodine, and instructions for iodine intake. There were no symptomatic adverse effects claimed to the town. Conclusions The distribution and consumption of stable iodine occurred in Miharu Town after the Fukushima disaster. To prepare for future nuclear emergencies, it is important to explain to both children and parents the need for intake of stable iodine, particularly among young children. Thyroid cancer after irradiation is a defined clinical entity, particularly among children (1). Childhood thyroid cancer after irradiation has been observed after radiation therapy or after exposure to environmental radiation after the release of radioactive iodine (1, 2). Examples of the latter include the atomic bombings of Hiroshima and Nagasaki (3), nuclear bomb testing in the Marshall Islands (4, 5), and the Chernobyl nuclear accident (6, 7). Children are at greater risk than adults of developing thyroid cancer after radiation (6), and childhood thyroid cancer after nuclear emergencies is of great public health concern. In a nuclear emergency, intake of stable iodine is a key strategy for preventing childhood thyroid cancer along with other preventive strategies, including evacuation, sheltering, and restrictions on the consumption of contaminated food and water (8). Ingestion of stable iodine reduces internal exposure in the thyroid by blocking the uptake of radioactive iodine because it saturates the thyroid gland (8). The timing of administration is optimally between 24 hours prior to and up to 2 hours after the expected onset of exposure, but it is reasonably effective even up to 8 hours later (8). However, there is limited information about operational issues, such as the acceptability and feasibility of implementation in actual cases (8). To our knowledge, except for evidence from Poland after the Chernobyl accident (9), there is no other documented report of the intake of stable iodine as a preventive strategy in a nuclear emergency. To prepare for future nuclear emergencies, investigations of the operational issues in an actual case are needed. On 11 March 2011, the Great East Japan Earthquake and tsunami struck the Fukushima Daiichi nuclear power plant (F1). This resulted in the scattering of radioactive substances, including radioactive iodine, and in unintentional radiation exposure among residents (10). The amount of radioactive iodine released after the Fukushima disaster (∼520 PBq) has been estimated to be about 10% of that after the Chernobyl accident (∼5300 PBq) (11). According to the 2013 United Nations Scientific Committee on the Effects of Atomic Radiation report published after this disaster, the estimated absorbed dose to the human thyroid after the Fukushima disaster was <100 mGy (12). Therefore, the distribution of stable iodine was not required, according to World Health Organization guidelines at the time of the disaster (13). However, because of time pressure and ambiguity at the time, four local governments [those of Miharu Town (14) and three evacuated towns] distributed iodine and provided instructions for the intake of stable iodine (15). Neither the national nor the prefectural governments distributed stable iodine, even though there was sufficient stored stable iodine to do so (15). Among the towns issuing a mandatory evacuation order, it was difficult to survey all residents because the distribution status and instructions about iodine intake varied according to the place of evacuation. Miharu Town, located west of F1, w (...truncated)