Findings announced from the Hanford Thy- roid Disease Study Final Report show that the risks of thyroid disease in study partici- pants were about the same regardless of the radiation dose they received from radioactive iodine-131 from the Hanford Nuclear Weapons Production Facility in Eastern Washington between 1944 and 1957.
While thyroid disease was found, researchers determined that rates disease in study participants were about the same as rates in other populations.
The Centers for Disease Control and Prevention (CDC) and Fred Hutchinson released the findings of the 13-year study in mid-June at a community meeting in Richland.
"We used the best scientific methods available, and we did not find an increased risk of thyroid disease in study participants from exposure to Hanford's iodine-131," said Dr. Paul Garbe, epidemiologist and CDC's scientific adviser for the study. "If there is an increased risk of thyroid disease, it is too small to observe."
The research team studied all types of thyroid diseases and examined how the rates varied in relation to participants' estimated radiation doses from Hanford's iodine-131.
"On the basis of a study population of 3,440 people, we found that people with higher doses of radiation had about the same amount of thyroid disease as people with lower doses," said Dr. Scott Davis, Fred Hutchinson's principal investigator for the study. "We analyzed the data a number of ways, and the results were the same."
The research team also found that the rates of thyroid disease in the people who participated in the study were generally consistent with the rates of disease in other populations in the United States, based on a review of published scientific literature conducted after the release of a draft report in 1999.
'As much detail as possible'
"Thyroid disease is fairly common in other populations across the country, especially among older people and women," Garbe said. "However, we understand the concern that people in the Hanford region have about thyroid disease, given their exposure to iodine-131, and we want to provide as much detail as possible about our findings and what they mean."
The study focused on people who were young children when exposed to iodine-131 from Hanford between 1944 and 1957. Iodine-131 accounted for most of the radiation dose to the people exposed to Hanford's radiation. Scientists believe that young children receive a higher dose to the thyroid gland than adolescents and adults for the same level of exposure and that the thyroid gland in young children may be more sensitive to the effects of radiation.
The study sampled people born between 1940 and 1946 to mothers who lived in Benton, Franklin, Adams, Walla Walla, Okanogan, Ferry, and Stevens counties in Eastern Washington. Each participant underwent a complete evaluation for thyroid disease. Detailed information about what participants ate and where they lived also were collected.
Participants had a wide range of possible doses to the thyroid gland, enabling researchers to compare groups of people who have similar characteristics (such as birth, diet and lifestyle) but different levels of exposure.
This approach of studying a single population of individuals with different levels of exposure has been used extensively in assessing the effects of radiation exposure in human populations.
A committee of the National Academy of Sciences evaluated the study at three stages. Other scientists and members of the public provided input throughout the study.
Congress mandated the study in 1988 after the U.S. Department of Energy made public documents revealing that large quantities of radioactive materials were released from the Hanford Nuclear Weapons Plant in the 1940s and 1950s, especially in 1945.
[Susan McClure is public-relations specialist for the Centers for Disease Control.]