Results announced today from the Hanford Thyroid Disease Study show no relationship between thyroid disease and exposures to radioactive iodine-131 (I-131) released from the Hanford Nuclear Site.
"This is a very impressive study given the large number of people who participated and the high level of community involvement in the study throughout its course," said Jeffrey P. Koplan, M.D., M.P.H., director, Centers for Disease Control and Prevention (CDC) and Agency for Toxic Substances & Disease Registry.
The draft report will be released by CDC and the Fred Hutchinson Cancer Research Center (FHCRC) at a 3 p.m. media briefing and 7 p.m. community meeting tonight (Jan. 28) in Richland, Wash.
"We looked at all types of thyroid disease and found no evidence that the number of cases was significantly elevated among those with higher I-131 doses," said Scott Davis, Ph.D., principal investigator for the study at FHCRC. "This was a very powerful study because it included a large number of people estimated to have a wide range of exposures to I-131. Each person was carefully evaluated for any evidence of thyroid disease. If the exposure to I-131 from Hanford had affected the thyroid health of as many people as you would predict from past studies in other populations exposed to radiation, this study would almost certainly have detected those effects," he said.
The study focused on a group of people exposed as children to I-131 released from Hanford during the years 1944 to 1957. The purpose of the study was to determine if there was a relationship in the study population between the risk of thyroid disease and different levels of thyroid radiation doses from I-131. This relationship was evaluated by determining if individuals with higher doses also had a higher risk of thyroid disease. Because iodine concentrates in the thyroid gland, the most likely health effect resulting from such exposures would be the development of thyroid disease. The thyroid diseases assessed in this study included thyroid cancer, benign thyroid nodules, hypothyroidism, hyperthyroidism and autoimmune thyroiditis.
"Studies like the HTDS cannot tell us if a specific person's thyroid disease is or is not caused by Hanford radiation. It can only tell us that in this specific group of people, we did not find a link between the risk of thyroid disease and their estimated thyroid radiation dose from Hanford," said the CDC scientific advisor for the study, Paul Garbe, D.V.M.
Study participants were selected from those born between 1940 and 1946 to mothers who lived in Benton, Franklin, Adams, Walla Walla, Okanogan, Ferry and Stevens counties. Researchers assessed the thyroid health for 3,441 people. Each study participant was interviewed and given physical, ultrasound and laboratory examinations to investigate possible problems with the thyroid gland. In addition, medical records were reviewed to identify thyroid diseases diagnosed before the study began.
Although the study found no evidence that thyroid disease risk was increased by I-131, it did show that participants with higher I-131 doses were somewhat more likely to have small abnormalities that were too small to be felt by a physician, but were detected by ultrasound scans. These abnormalities are quite common among people not exposed to I-131, and physicians agree they do not likely represent a disease. Also, participants with higher doses showed very slightly lower levels of serum calcium in their blood tests. This decrease, though unexpected, was well within normal ranges for a healthy person.
While conducting the study, researchers found that death rates in the study population, particularly for congenital anomalies and conditions that occurred late in pregnancy or in the first seven days after birth, were slightly higher than death rates in the state of Washington for the same period. However, none of this increase was related to thyroid disease.
This is a preliminary analysis, and the reasons for this statistically significant elevation in mortality are not known. The highest rate of overall excess in mortality occurred prior to the beginning of Hanford Operations. Another study of infant and fetal deaths in eight Washington counties during the years 1940 to 1952 currently is being conducted by the Agency for Toxic Substances and Disease Registry with the results expected in late spring. Though the counties in this study are different from those included in the thyroid disease study, the study will provide additional information on rates of infant mortality, fetal death and pre-term birth by geographic area.
The nine-year, $18 million Hanford Thyroid Disease Study was mandated by Congress in 1988 after the Department of Energy (DOE) made public thousands of documents that showed large quantities of radioactive materials were released from the Hanford Nuclear Reservation during its early years of operation in the 1940s and 1950s. The material that accounted for most of the radiation dose to exposed individuals was I-131. The release of these documents raised public concerns about possible health effects of exposure to I-131, which prompted the study.
In response to the high level of public interest in the study, the results were released earlier than originally planned. The results are in draft form -- and open to public comment -- from CDC and the FHCRC. Public comments will be accepted through April 1, 1999.
The draft report also will be reviewed by the National Academy of Sciences' Committee on Assessment of CDC Radiation studies.
Members of the public who want to be sent more detailed information, or have specific questions regarding this study, should call:
HANFORD THYROID DISEASE STUDY
TOLL-FREE PHONE: 1-800-638-4837
(Available weekdays; also offers voice mail system)
Or visit the following Web sites:
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(Press release from the CDC, posted here for reporters' convenience.)
For immediate release: Jan. 28, 1999
Contact: CDC Division of Media Relations 404-639-3286