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External Radiation Dose, Obesity, and Risk of Childhood Thyroid Cancer after the Fukushima Daiichi Nuclear Power Plant Accident

The Fukushima Health Management Survey

Ohira, Tetsuya1,2; Ohtsuru, Akira1,3; Midorikawa, Sanae1,3; Takahashi, Hideto1,4; Yasumura, Seiji1,5; Suzuki, Satoru1; Matsuzuka, Takashi1,6; Shimura, Hiroki1,7; Ishikawa, Tetsuo1,8; Sakai, Akira1,9; Suzuki, Shinichi10; Yamashita, Shunichi1,11; Yokoya, Susumu1,12; Tanigawa, Koichi1; Ohto, Hitoshi1; Kamiya, Kenji1,13 for the Fukushima Health Management Survey group.

doi: 10.1097/EDE.0000000000001058
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Background: The 2011 Great East Japan Earthquake led to a nuclear accident at Fukushima Daiichi Nuclear Power Plant. This study examines the associations of radiation dose and lifestyle factors with incidence of thyroid cancer in Fukushima.

Methods: We designed a prospective study with 300,473 participants aged 18 years or younger who underwent thyroid examinations from October 2011. Follow-up surveys were conducted through June 2017, and 245,530 participants (123,480 men and 122,050 women, 82% follow-up) received follow-up examinations. Fukushima Prefecture was divided into five areas based on individual external radiation dose. We calculated relative risks and 95% confidence intervals (CIs) for thyroid cancer in each area, with area of lowest dose as reference, using age-adjusted Poisson regression models. We also calculated risks associated with overweight and obesity.

Results: The incidence per 100,000 for Groups A (highest dose), B, C, D, and E (lowest dose) were 13.5, 19.2, 17.3, 9.0, and 8.3, respectively. Compared with Group E, the age-adjusted risks (95% CIs) were 1.62 (0.59–4.47) for group A, 2.32 (0.86–6.24) for group B, 2.21 (0.82–5.94) for group C, and 1.02 (0.36–2.86) for group D. Obesity was positively associated with thyroid cancer incidence; the age- and sex-adjusted risk of thyroid cancer was 2.26 (1.03-4.95) for obese individuals compared non-obese.

Conclusions: Regional differences in radiation dose were not associated with increased risk of thyroid cancer among children in Fukushima within 4–6 years after the nuclear power plant accident. Obesity may be an important factor for further follow-up in Fukushima.

1Radiation Medical Science Center for the Fukushima Health Management Survey, Fukushima Medical University, Fukushima, Japan

2Department of Epidemiology, Fukushima Medical University School of Medicine, Fukushima, Japan

3Department of Radiation Health Management, Fukushima Medical University School of Medicine, Fukushima, Japan

4National Institute of Public Health, Saitama, Japan

5Department of Public Health, Fukushima Medical University School of Medicine, Fukushima, Japan

6Department of Otorhinolaryngology, Fukushima Medical University School of Medicine, Fukushima, Japan

7Department of Laboratory Medicine, Fukushima Medical University School of Medicine, Fukushima, Japan

8Department of Radiation Physics and Chemistry, Fukushima Medical University School of Medicine, Fukushima, Japan

9Department of Radiation Life Sciences, Fukushima Medical University School of Medicine, Fukushima, Japan

10Department of Thyroid and Endocrinology, Fukushima Medical University School of Medicine, Fukushima, Japan

11Atomic Bomb Disease Institute, Nagasaki University, Nagasaki, Japan

12Thyroid and Endocrine Center, Fukushima Medical University, Fukushima, Japan

13Research Institute for Radiation Biology and Medicine, Hiroshima University, Hiroshima, Japan.

Sources of financial support: This work was supported by the National Health Fund for Children and Adults Affected by the Nuclear Incident for design and conduct of the study.

Conflicts of interest: There is no conflict of interest.

A statement on availability of data: The data from this study cannot be made publicly available because the data of the Fukushima Health Management Survey belongs to the government of Fukushima prefecture and can only be used within that organization.

ACKNOWLEDGMENTS: The authors thank the staff of the Fukushima Health Management Survey for their important contributions.

FUNDING/SUPPORT: This survey was supported by the National Health Fund for Children and Adults Affected by the Nuclear Incident for design and conduct of the study. The findings and conclusions of this article are solely the responsibility of the authors and do not represent the official views of the Fukushima Prefecture government.

Address correspondence and reprint requests to: Tetsuya Ohira, MD., PhD. Department of Epidemiology, Fukushima Medical University School of Medicine, Fukushima 960-1295, Japan. Phone +81-24-547-1344, Fax +81-24-547-1336. E-mail: teoohira@fmu.ac.jp

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