Long-term follow-up of Hiroshima and Nagasaki atomic bomb survivors indicates that risk of thyroid cancer remains elevated even long after exposure. These results were published in the Journal of the American Medical Association.
The thyroid is a gland located at the bottom of the throat. It is responsible for producing hormones that aid in metabolism.
Radiation exposure is known to increase the risk of thyroid cancer, but it’s uncertain how long the effects of exposure persist. To assess the occurrence of thyroid cancer and other thyroid disorders many years after radiation exposure, researchers evaluated survivors of the Hiroshima and Nagasaki atomic bombs. The study assessed over 4000 survivors 55-58 years after the bombings.
The average age of study subjects was 70 years, and 67% were women. Information was collected about thyroid cancer, benign thyroid nodules and cysts, and autoimmune thyroid disease. Subjects with high levels of radiation exposure were compared to subjects with lower radiation exposure.
- 32% of the men and 51% of the women had evidence of thyroid disease.
- Thyroid cancer was present in 2.2% of subjects. Risk of thyroid cancer increased with the dose of radiation received.
- Risk of benign thyroid nodules also increased with increasing radiation dose.
- There was no link between increasing radiation exposure and increasing risk of autoimmune thyroid disease.
- In this population, radiation exposure was thought to account for 37% of thyroid cancers, 31% of benign thyroid nodules, and 25% of thyroid cysts.
The researchers conclude that 55-58 years after exposure, survivors of the Hiroshima and Nagasaki atomic bombs continue to have an increased risk of thyroid cancer. There was a clear effect of radiation dose, with the greatest risk of thyroid cancer in those who had received the greatest radiation dose. The researchers note, “Careful examination of the thyroid is still important long after radiation exposure, especially for people exposed at younger ages.”
Reference: Imaizumi M, Usa T, Tominaga T et al. Radiation Dose-Response Relationships for Thyroid Nodules and Autoimmune Thyroid Diseases in Hiroshima and Nagasaki Atomic Bomb Survivors 55-58 Years After Radiation Exposure. JAMA . 2006;295:1011-1022.