Radioactive iodine linked to thyroid disease

NEW YORK (Reuters Health) - The long-term risk of developing a tumor in the thyroid gland or autoimmune thyroiditis, a progressive inflammatory disease of the thyroid, is increased after exposure to radioactive iodine in childhood, according to a re-analysis of data from children exposed to radiation from a nuclear test site in Nevada.

Since 1965, researchers have been studying children exposed to radioactive iodine from nuclear weapons testing at the Nevada Test Site from 1951 through 1962.

In 1993, Dr. Joseph L. Lyon, of the University of Utah School of Medicine, Salt Lake City, and colleagues, reported that among the 2,497 subjects examined, there was an association between radiation exposure from the Nevada Test Site and thyroid tumors.

The researchers have now used newly corrected dose estimates and disease outcomes to reassess the association. The new results are published in the current issue of the journal Epidemiology.

In children who received the highest radiation dose, the risk of thyroid tumors rose from 3.4-fold in the earlier evaluation to 7.5-fold. For thyroiditis, the risk increased from 1.1- to 2.7-fold, with a 4.9-fold excess risk for exposure to each Gy unit (gray = absorbed dose of radiation). The risk could not be estimated for malignant thyroid tumors.

"This is the first report of such a relationship in a U.S. population; hence, we believe that this (study group) represents a unique opportunity to provide further assessment of a range of exposures and disease end points among U.S. citizens," Dr. Lyon's team writes. "Further follow-up of this (study group may increase our understanding of the long-term health consequences of exposure to radioactive iodine regardless of its origin in reactors, accidents, or nuclear detonations."

SOURCE: Epidemiology, November 2006.