• E-mail
• Print
• Comment
• Font Size
• Digg
• del.icio.us
• Discuss article

Thyroid Woes a Long-Term Risk After Exposure to Radiation

Posted on: Tuesday, 7 March 2006, 15:00 CST

By Joe Bauman Deseret Morning News

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.

However, he wrote, "the risk per unit dose following exposure in childhood is higher than for any other radiation-induced malignancy."

In a Deseret Morning News telephone interview, Boice said the Japanese study had two notable findings:

"One, that nearly 60 years after being exposed to the atomic bombs in Hiroshima and Nagasaki, a biological effect on the thyroid could be detected," he said. "And so that indicates that this risk has stayed with the children that were exposed for almost 60 years."

He thought that length of time was especially interesting. The risk appears to be decreasing with the years but was still present, he said.

"The second thing was, they did a rather exhaustive study, looking for the so-called autoimmune disease." Japanese researchers used the latest biological tests to look for hormones in the blood that would indicate increased risk of autoimmune-type thyroid disease. "They found absolutely no evidence for any association with radiation" in such diseases, he said.

For other thyroid diseases, including cancer, a direct association appears to fit with dosage, he said. This applies to children, as people who were adults at time of exposure did not show this risk.

"The atomic bombs were a fraction of a second," Boice said. "There was whole-body exposure. The dose was delivered at a very high rate."

In comparison, with ingested fallout, the exposure usually would be to a much lower level of radiation but continued over a longer period. Radioactive Iodine-131 has a half-life of eight days, compared with the nearly instantaneous exposure from a bomb's flash.

With fallout, the commonest way that the thyroid was exposed is through drinking milk that contained radioactive iodine, usually I- 131. The iodine particles fell from clouds drifting from the Nevada Test Site, cows grazed on contaminated fields and children drank milk from the cattle.

J Truman, a Malad resident who grew up in southwestern Utah and is director of the advocacy group Downwinders, was critical of the CDC for killing the Utah thyroid study.

"Just as the Japanese are finding damages from the exposures they received are still causing cancers and other problems 60 years later," he wrote in an e-mail to the Deseret Morning News, "a similar study ongoing now for 40 years at the U. of U. started to show new effects and relationships."

But then, Truman added, the U. study was terminated before it could be finished.

E-mail: bau@desnews.com

Source: Deseret News (Salt Lake City)

More News in this Category