RERF Report No. 1-17

Paper published in J Clin Endocrinol Metab§“Thyroid dysfunction and autoimmune thyroid diseases among atomic-bomb
survivors exposed in childhood 62–66 years after radiation exposure”
Misa Imaizumi, Waka Ohishi, Eiji Nakashima, Nobuko Sera, Kazuo Neriishi, MichikoYamada, Yoshimi Tatsukawa, Ikuno Takahashi, Saeko Fujiwara, Keizo Sugino, Takao
Ando, Toshiro Usa, Atsushi Kawakami, Masazumi Akahoshi, Ayumi Hida
J Clin Endocrinol Metab 2017 (July); 102(7):2516-24(doi: https://doi.org/10.1210/jc.2017-00102)

Study Findings
A thyroid study involving atomic bomb survivors exposed as children (younger than 10 yearsold) showed no association between A-bomb radiation dose to the thyroid and the prevalence*of thyroid dysfunction or autoimmune thyroid diseases 62 to 66 years after the atomicbombings.
* Prevalence represents the proportion of people in a population with a disease at a certain point
in time (at an examination) regardless of the timing of disease onset.

Explanation
The participants of the Adult Health Study (AHS) exposed to atomic bomb radiation before
the age of 10 were studied for an association between A-bomb radiation dose and thyroid
dysfunction/autoimmune thyroid diseases. The AHS has followed the health status of A-bomb
survivors in Hiroshima and Nagasaki through biennial health examinations since 1958.
1. Study purpose
It is important from a public health perspective to know whether radiation effects on thethyroid persist into adulthood, long after childhood exposure to radiation. It is known that those
exposed to radiation as children have a higher risk of developing thyroid cancer than thoseexposed as adults. It is not clear whether there are long-term effects of childhood exposure to
low-to-medium doses of radiation on thyroid dysfunction and autoimmune thyroid diseases. The
objective of this study is to examine the association between atomic bomb radiation exposureand thyroid dysfunction/autoimmune thyroid diseases among A-bomb survivors exposed aschildren more than 60 years ago.
2. Study methods
Interviews and blood tests (to measure thyroid function and antithyroid autoantibodies) were1

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performed for 3,087 A-bomb survivors who were younger than 10 years of age at the time of theatomic bombings and had participated in AHS health examinations from 2007 to 2011. In thispopulation, an association between radiation dose to the thyroid and the prevalence of thyroid
dysfunction and autoimmune thyroid diseases was studied for the 2,668 participants whose
atomic bomb radiation dose to the thyroid had been estimated (1,213 men and 1,455 women;mean age: 68.2 years; mean dose: 0.182 Gy; dose range: 0–4.040 Gy).
3. Study results(1) Prevalence was 7.8% for hypothyroidism**, 1.2% for hyperthyroidism***, and 21.5%
for positive antithyroid autoantibody. All cases of hyperthyroidism were found to becaused by Graves’ disease.
(2) Thyroid radiation dose was not associated with the prevalence of hypothyroidism,
hyperthyroidism, or positive antithyroid autoantibody. Hypothyroidism cases weredivided into antithyroid autoantibody-positive and -negative for analysis. Neither wasassociated with thyroid radiation dose.
(3) Other studies looking at radiation effects in the thyroid, such as post-Chernobyl studies,used different diagnostic criteria for thyroid dysfunction. An additional analysis wasconducted by diagnosing hypothyroidism and hyperthyroidism based on the diagnostic
criteria used in these other studies, but again, no association with thyroid radiation dose
was observed.
**/*** Hypothyroidism is a condition in which the body lacks sufficient thyroid hormone in theblood. Symptoms include fatigue, hair loss, and swelling. Hyperthyroidism is a condition inwhich the body has excessive amounts of thyroid hormone in the blood. Symptoms include
excessive sweating, weight loss, and palpitations. Typically, the most common cause of
hypothyroidism is chronic thyroiditis, and that of hyperthyroidism is an autoimmune thyroid
disease called Graves’ disease. Graves’ disease is a thyroid disease caused by a breakdown of
the immune system. People who test positive for antithyroid autoantibody are at a high riskof chronic thyroiditis.

Study SignificanceThis is the first study among A-bomb survivors to examine effects on adulthood thyroid
dysfunction and autoimmune thyroid diseases from radiation exposure during childhood, whenradiation sensitivity is high. The study, which is based on data accumulated over more than 60years since radiation exposure, did not detect significant radiation effects. However, this was across-sectional study based on a study of A-bomb survivors at a certain point in time, like otherstudies that have looked into radiation effects on thyroid dysfunction. It is therefore necessary to2

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conduct a longitudinal study over time to better understand radiation effects on the thyroid.
The Radiation Effects Research Foundation has studied A-bomb survivors and their offspring inHiroshima and Nagasaki for around 70 years. RERF’s research achievements are considered the principal
scientific basis for radiation risk assessment by the United Nations Scientific Committee on the Effects ofAtomic Radiation (UNSCEAR) and for recommendations regarding radiation protection standards by theInternational Commission on Radiological Protection (ICRP). RERF expresses its profound gratitude tothe A-bomb survivors and survivors’ offspring for their cooperation in our studies.
§The Journal of Clinical Endocrinology & Metabolism, the most cited journal in its field, publishes

clinical research and practice information involving the pathophysiology, diagnosis, and treatment ofendocrine and metabolic disorders. (Impact factor in 2016/2017: 5.455)

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