Iodine deficiency, supplements affect thyroid cancer risk in children exposed to radioact...( Exposure to radioactive iodines mainly...),Health

Exposure to radioactive iodines, mainly iodine 131 (I-131), in childhood is associated with an increased risk of thyroid cancer. Importantly, both iodine deficiency and supplementation appear to modify this risk, according to a new study in the May 18 issue of the Journal of the National Cancer Institute.

The accident at the Chernobyl nuclear power plant in April 1986 resulted in widespread radioactive contamination, particularly in parts of Belarus, the Russian Federation, and the Ukraine. For people living in these areas, the main radiation dose was to the thyroid and came from exposure to I-131 from drinking contaminated milk. (The thyroid uses iodine to make thyroid hormone.) It has been estimated that the thyroids of several thousand children in Belarus received I-131 doses of at least 2 Gray, a unit of absorbed radiation dose. (People are usually exposed to a background radiation from natural sources of only 1 to 2 mGy per year.) In addition, a very large increase in the incidence of thyroid cancer in young people was observed as early as 5 years after the accident in Belarus and slightly later in the Russian Federation and the Ukraine. However, important questions remained about the magnitude of the potential modifying effect of iodine deficiency, which was common in most of the affected areas at the time of the Chernobyl accident.

To evaluate the risk of thyroid cancer after exposure to radioactive iodine in childhood and investigate factors that might modify this risk, Elisabeth Cardis, Ph.D., of the International Agency for Research on Cancer in Lyon, France, and colleagues conducted a casecontrol study of 276 thyroid cancer patients and 1,300 control subjects in Belarus and the Russian Federation who had been age 15 years or younger at the time of the Chernobyl accident.

The researchers observed a strong doseresponse relationship between radiation dose to the thyroid received during childhood and the risk of thyroid cancer.
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Contact: Sarah L. Zielinski
jncimedia@oupjournals.org
301-841-1287
Journal of the National Cancer Institute
17-May-2005

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