Takemi Program in International Health
The Takemi Program in International Health seeks to improve health and health systems around the world by welcoming mid-career health professionals and scholars to the Harvard T. H. Chan School of Public Health to conduct path breaking research and develop their leadership skills.
665 Huntington Avenue, Bldg. 1, Room 1210
Boston, MA 021151, USA
Stable Iodine Implementation as a Thyroid Protection Measure in Nuclear Emergencies
Yoshitaka Nishikawa,1,2,3 Chiaki Suzuki,1,2 Fumiya Oguro,1 Aya Goto,3,4 Masaharu Tsubokura 1,4
¹ Hirata Central Hospital
² Kyoto University
³ Harvard TH Chan School of Public Health
⁴ Fukushima Medical University
Introduction
Thyroid cancer has been recognized as a critical health concern following nuclear emergencies, due to the release of radioactive iodine, which concentrates in the thyroid gland.
Four key preventive measures include evacuation, sheltering in place, avoiding contaminated food or drink, and taking stable iodine, recommended by WHO and national regulatory authorities. Stable iodine can saturate the thyroid gland, thereby reducing the uptake of radioactive iodine and effectively lowering the risk of thyroid cancer development.
After the 2011 FDNPP accident, extensive thyroid screening programs were initiated with the goal of detecting and preventing serious health outcomes. Although the radiation dose was significantly lower compared to that of the Chernobyl incident, an apparent rise in thyroid abnormalities was observed—largely attributed to the “screening effect,” wherein increased surveillance leads to more frequent detection of otherwise subclinical thyroid lesions.
Aims
This study aimed at examining the intake rate of stable iodine and the association between stable iodine intake and thyroid ultrasound screening outcomes after the FDNPP accident.
Methods
Setting: Thyroid screening at Research Institute of Radiation Safety for Disaster Recovery Support (RSDRS).
Participants: Children born between April 1998 and March 2012 in Miharu Town.
- Study Context: Fukushima Prefecture (59 Municipalities) – 7/59 distributed stable iodine after disaster, 4/59 instructed intake, 3/59 instructed intake and evacuated. Miharu Town was the 1/59 that instructed intake without evacuation.
- Analysis: Coarsened exact matching for age and sex to estimate average treatment effect. Multivariable logistic regression performed to adjust for sex and age at disaster.
- Thyroid Ultrasound Categories: A1 (No nodule or cyst), A2 (Nodule <5.0 mm and/or cyst <20.1 mm), B (Further examination necessary), C (Urgent need for further examination).
Results
Key Findings
Study Population: All participants n = 2,129. Answered for stable iodine n = 1,974. Intake n = 1,095, No intake n = 879.
- Intake Rate of Stable Iodine: Mothers 34.9%, Children 63.5%. Awareness raising and effective communication with children, their guardians, and pregnant women are important for nuclear emergency preparedness.
- Stable Iodine and Thyroid Outcomes: No association between stable iodine intake and thyroid screening outcomes. This is probably due to the relatively low radiation doses after the FDNPP accident.
- Thyroid Effects: No differences were observed in parenchymal heterogeneity and thyroid volume. This finding supported that adverse effects of single-dose stable iodine on the thyroid gland would be minimal.
Statistical Results
Multivariable Logistic Regression Results: Stable Iodine Intake (Reference: No intake) showed an Odds Ratio of 0.839 (0.393, 1.8) with p-value 0.647, indicating no significant association. Sex (Reference: Female) had an Odds Ratio of 0.369 (0.154, 0.809) with p-value 0.012. Age at disaster showed an Odds Ratio of 1.188 (1.072, 1.329) with p-value 0.001.
Conclusions
Awareness raising and effective communication with children, their guardians, and pregnant women are important for nuclear emergency preparedness. The study found significant differences in intake rates between mothers (34.9%) and children (63.5%), highlighting the need for targeted communication strategies.
No association between stable iodine intake and thyroid screening outcomes was found, probably due to the relatively low radiation doses after the FDNPP accident. Additionally, no differences were observed in parenchymal heterogeneity and thyroid volume, supporting that adverse effects of single-dose stable iodine on the thyroid gland would be minimal.
Acknowledgements
We would like to thank all the staff who engaged this screening at the RSDRS and municipality officers involved. The screening was conducted by RSDRS as a practice, and all basic support was provided by RSDRS. Written consent was obtained from the participants (guardians). Approval was obtained from institutional review boards.