TUESDAY, Feb. 28, 2006 (HealthDay News) -- It's been 60 years since atomic bombs fell on the cities of Hiroshima and Nagasaki in Japan, but survivors are still struggling with the effects, according to new research.
The latest research found that survivors of the attacks continue to develop thyroid nodules -- either benign or cancerous -- and the presence of these nodules is in direct proportion to the radiation dose they received.
The researchers also found that the younger a person was at the time of the bombings, the more likely they were to develop thyroid nodules. However, the research found no connection between radiation exposure and thyroid autoimmune diseases.
Thyroid nodules result from an excess growth of thyroid tissue and can be either benign or malignant. External radiation exposure is one of the known causes of thyroid nodules, according to background information in the study.
"Careful examination and follow-up of thyroid diseases are still important long -- 55 to 58 years -- after radiation exposure because the present results indicate that radiation dose effects on thyroid nodules, including benign and malignant nodules, were significantly higher in those exposed when young. And the younger-exposed people are now becoming the cancer-prone ages," said the study's lead author, Dr. Misa Imaizumi, a research scientist and chief of the division of radiology in the department of clinical studies at the Radiation Effects Research Foundation in Nagasaki, Japan.
The new findings appear in the March 1 issue of the Journal of the American Medical Association.
Five years after the bombs were dropped, the Radiation Effects Research Foundation (known then as the Atomic Bomb Casualty Commission) was established to study the long-term effects of such extreme radiation exposure in more than 120,000 survivors.
The new study includes nearly 4,100 survivors from that cohort. The study was conducted between March 2000 and February 2003, with study participants averaging 70 years of age. The study included 2,739 women and 1,352 men.
Nearly 45 percent of the participants had some type of thyroid disease, including nodules, autoimmune disease, hypothyroidism and hyperthyroidism, according to the study. Women were more likely to have thyroid problems than men -- 51 percent of women vs. 32 percent of men.
The study found that the higher the radiation exposure, the more likely a person was to develop a thyroid nodule. The researchers estimate that 37 percent of malignant tumors, 31 percent of benign nodules and 25 percent of cysts discovered during ultrasound as part of the study were associated with bomb-linked radiation exposure.
Age at the time of exposure was also an important factor in the development of thyroid nodules. The most significant effects were seen in those under 10 at the time of exposure.
The study found no association between radiation exposure and autoimmune thyroid diseases, such as Graves' disease.
"The effects of radiation exposure may last for a lifetime," said Dr. John Boice Jr., author of an accompanying editorial in the same issue of the journal and scientific director of the International Epidemiology Institute in Rockville, Md. "Even exposure that occurred many years in the past still can have biological effects today."
That information may be important not just for survivors of atomic bombs, but also for anyone who's had medical treatment with radiation, particularly during the 1940s or '50s.
Boice, who is also a professor of medicine at the Vanderbilt University School of Medicine in Nashville, Tenn., noted that anyone with a history of such treatment needs to let their current physician know about it, so they can receive proper follow-up. However, he stressed that the risk remains low, and that risks from common radiation exposures, such as through X-ray or CT scans, are much lower still.
To learn more about how radiation affects the body, visit the U.S. Nuclear Regulatory Commission.