Conference Coverage

Early A-bomb radiation not linked to thyroid function




LAKE BUENA VISTA, FLA. – No link was found between atomic bomb radiation exposure in childhood and autoimmune thyroid disease or thyroid dysfunction in a study of nearly 2,700 Hiroshima and Nagasaki atomic bomb survivors.

Exposure among the 2,668 survivors included in the survey occurred prior to age 10 years, with follow-up more than 60 years later. The prevalence of anti–thyroid peroxidase (anti-TPO) positivity and/or antithyroglobulin (anti-Tg) antibodies, hypothyroidism, and hyperthyroidism was 21.5%, 4.8%, and 1.2%, respectively, when measured between October 2007 and October 2011, Dr. Misa Imaizumi of the Radiation Effects Research Foundation, Nagasaki, Japan, reported at the International Thyroid Congress.

All patients with hyperthyroidism had Graves disease, and the prevalence of anti–thyroid antibody–positive and –negative hypothyroidism was 2.1% and 2.7%, respectively, she said at the meeting held by the American Thyroid Association, Asia-Oceania Thyroid Association, European Thyroid Association, and Latin American Thyroid Society.

An analysis showed no significant dose-response relationship between radiation exposure and any thyroid disease (P greater than .1). This remained true when additional analyses were performed using alternative definitions of hypothyroidism and hyperthyroidism, such as subclinical, antibody-positive, and antibody-negative disease, she noted.

Study subjects included 1,213 men and 1,455 women with known atomic bomb thyroid radiation doses during childhood (mean thyroid dose, 0.182 Gy; median dose, 0.018 Gy).

“As you know, the risk of thyroid cancer increases by radiation exposure, and an increased risk of thyroid cancer has been observed in atomic bomb survivors. It is also well-known that high-dose radiation exposure – several 10s of gray – induces hypothyroidism, but the influence of radiation exposure by low to moderate doses – less than 5 gray – on thyroid dysfunction has been debated, and [studies of] the effects of atomic bomb radiation have been inconclusive,” Dr. Imaizumi said.

Because the radiation sensitivity of the thyroid is believed to be higher in children than in adults, she and her colleagues at the Radiation Effects Research Foundation – a Japan/U.S. collaboration that studies the effects of atomic bomb radiation for peaceful purposes – investigated the effects of childhood exposure on later thyroid dysfunction. Evaluations were conducted between October 2007 and October 2011; patients had a mean age of 68 years at the time of evaluation.

Information about previous thyroid diseases was obtained by questionnaire and by measurement of T4, thyroid-stimulating hormone, anti-TPO antibody, and anti-Tg antibody levels.

“In conclusion, associations between radiation exposure and thyroid dysfunction and other thyroid disease were not found in atomic bomb survivors 60 years after exposure in childhood,” she said.

Dr. Imaizumi reported having no relevant financial disclosures.

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