Thyroid woes a long-term risk after exposure to radiation

In what might have implications for Utahns exposed to radioactive fallout in the 1950s and '60s, a new Japanese study concludes the danger of thyroid disease continues for many decades after exposure to atomic bomb radiation.

The report published in the March 1 edition of the Journal of the American Medical Association says that among the 4,091 Japanese atomic bomb attack survivors examined almost 60 years after the attacks on Hiroshima and Nagasaki, thyroid disease was identified in 1,833, or 44.8 percent of the participants.

Last year, the Centers for Disease Control discontinued a study headed by the University of Utah's Dr. Joseph L. Lyon of thyroid abnormalities among downwinders exposed to fallout from atomic testing in Nevada. That study, a follow-up examining people who were children during above-ground nuclear tests at the Nevada Test Site, ended after an expenditure of $8 million.

Although only 1,700 of a planned 4,500 people were examined, Lyon told the Deseret Morning News last June, "We identified several hundred cases of disease."

The method of exposure is different between direct atomic bomb blasts and fallout. But what is striking about the Japanese study is that for children exposed to atomic bomb radiation, thyroids continued to develop abnormalities nearly six decades after the momentary exposure.

In the JAMA study, Japanese scientists examined people who were exposed through the flash of radiation released when atomic bombs went off at Hiroshima and Nagasaki in 1945. The leader of the study was Dr. Misa Imaizumi of the Radiation Effects Research Foundation, Nagasaki.

"A significant linear radiation dose response for thyroid nodules, including malignant tumors and benign nodules, exists in atomic bomb survivors," the study says. "However, there is no significant dose response for autoimmune thyroid diseases."

The Japanese study included a "comprehensive thyroid disease survey between 2000 and 2003," JAMA said.

It notes that "55 to 58 years after radiation exposure, a significant linear dose-response relationship existed in the prevalence of not only malignant thyroid tumors but also benign thyroid nodules and that the relationship was significantly higher in those exposed at younger ages."

Autoimmune thyroid diseases were not found to be significantly associated with radiation exposure, the JAMA article says.

John D. Boice Jr., scientific director of the International Epidemiology Institute in Rockville, Md., wrote an editorial published by JAMA, discussing the study. It noted that there was no significant increased risk of thyroid cancer for people who were exposed after age 20, and that radiation-induced thyroid cancers are rarely fatal.