July 5, 2006 In a study of thyroid cancer after the Chornobyl accident in 1986, researchers at Columbia University's Mailman School of Public Health report that exposure to radioactive iodine ingested through the food chain increases the risk of thyroid cancer in children and adolescents. The study is published in the July 5 issue of the Journal of the National Cancer Institute.
The 1986 accident at the Chornobyl nuclear power plant exposed large numbers of people in Belarus, Ukraine, and the Russian Federation to highly radioactive material. Numerous studies have shown that exposure to certain types of radiation increases the risk of thyroid cancer in children and adolescents. However, up until now, few studies examined the effects of exposure to radioactive iodines, which can get into the food chain, and only three studies measured cancer risk from the Chornobyl-related exposures.
The team of researchers at the M ailman School of Public Health, with colleagues, screened more than 13,000 people for thyroid cancer who were under 18 at the time of the Chornobyl accident and lived in highly contaminated areas of Ukraine. The researchers estimated each participant's individual radiation dose using thyroid radioactivity measurements made shortly after the accident and interview data obtained during screening.
The researchers found 45 cases of thyroid cancer in the screened group in comparison with the 11.2 cases expected without the accident. Subjects had a tendency toward lower risk of thyroid cancer with increasing age at the time of the exposure. The authors suggest that exposure to radioactive fallout from the Chornobyl accident increased thyroid cancer risk in those exposed as children and adolescents.
“In young children and adolescents, thyroid gland tissue requires large amounts of iodine coming primarily from food,” said Geoffrey R. Howe, PhD, professor of epidemiology at the Mailman School and principal investigator. “If radioactive iodine gets into the food chain, as was the case in Chornobyl, children and adolescents accumulate large amounts of radioactive iodines in their glands. This exposes the thyroid tissues to the radiation which in turn, increases the chance of getting thyroid cancer and other diseases of the thyroid gland later in life.”
The researchers estimate that 75% of the thyroid cancer cases would have been avoided in the absence of radiation. “This estimate demonstrates a substantial contribution of radioactive iodines to the excess of thyroid cancer that followed the Chornobyl accident,” observed Dr. Howe.
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