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Autoimmune Thyroiditis and Exposure to Iodine 131 in the Ukrainian Cohort Study of Thyroid Cancer and Other Thyroid Diseases after the Chornobyl Accident: Results from the First Screening Cycle (1998–2000)

Institute of Endocrinology and Metabolism (M.D.T., V.A.O., O.V.E., T.I.B., V.V.M., G.M.T., V.M.S., V.P.T.), 04114 Kyiv, Ukraine; Scientific Center for Radiation Medicine (I.A.L.), Academy of Medical Sciences, 04050 Kyiv, Ukraine; Division of Cancer Epidemiology and Genetics (A.V.B., J.H.L., A.C.B., I.J.M., E.R., M.H.), National Cancer Institute, and Clinical Endocrinology Branch (J.R.), National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892-7238; Department of Medicine (R.J.M.), The Thyroid Center, and Department of Pathology (D.J.F.), College of Physicians and Surgeons, and Department of Epidemiology (L.B.Z., G.R.H.), Mailman School of Public Health, Columbia University, New York, New York 10032; and Department of Radiation and Radiological Sciences (A.B.B.), School of Medicine, Vanderbilt University, Nashville, Tennessee 37232

Address all correspondence and requests for reprints to: Alina Brenner, M.D., Ph.D., Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, 6120 Executive Boulevard, Room 7090, Bethesda, Maryland 20892-7238. E-mail: brennera{at}mail.nih.gov.

Context: Due to the Chornobyl accident, millions were exposed to radioactive isotopes of iodine and some received appreciable iodine 131 (¹³¹I) doses. A subsequent increase in thyroid cancer has been largely attributed to this exposure, but evidence concerning autoimmune thyroiditis (AIT) remains inconclusive.

Objective: The objective of the study was to quantify risk of AIT after ¹³¹I exposure.

Design/Setting/Participants: Baseline data were collected from the first screening cycle (1998–2000) of a large cohort of radiation-exposed individuals (n = 12,240), residents of contaminated, iodine-deficient territories of Ukraine. Study individuals were under the age of 18 yr on April 26, 1986, and had thyroid radioactivity measurements made shortly after the accident.

Outcomes: AIT was defined a priori based on various combinations of elevated antibodies to thyroid peroxidase (ATPO), TSH, and clinical findings; elevated ATPO were considered to be an indicator of thyroid autoimmunity.

Results: No significant association was found between ¹³¹I thyroid dose estimates and AIT, but prevalence of elevated ATPO demonstrated a modest, significant association with ¹³¹I that was well described by several concave models. This relationship was apparent in individuals with moderately elevated ATPO and euthyroid, thyroid disease-free individuals.

Conclusions: Twelve to 14 yr after the Chornobyl accident, no radiation-related increase in prevalence of AIT was found in a large cohort study, the first in which ¹³¹I thyroid doses were estimated using individual radioactivity measurements. However, a dose-response relationship with ATPO prevalence raises the possibility that clinically important changes may occur over time. Thus, further follow-up and analysis of prospective data in this cohort are necessary.