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Evgenia Ostroumova,¹ Alina Brenner,¹ Valery Oliynyk,² Robert McConnell,³ Jacob Robbins,⁴ Galina Terekhova,² Lydia Zablotska,⁵ Ilya Likhtarev,⁶ Andre Bouville,¹ Viktor Shpak,² Valentin Markov,² Ihor Masnyk,¹ Elaine Ron,¹ Mykola Tronko,² and Maureen Hatch¹

¹Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA; ²Institute of Endocrinology and Metabolism, Kyiv, Ukraine; ³Department of Medicine, The Thyroid Clinic, College of Physicians and Surgeons, Columbia University, New York, New York, USA; ⁴Clinical Endocrinology Branch, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA; ⁵Department of Epidemiology, Mailman School of Public Health, Columbia University, New York, New York, USA; ⁶Scientific Center for Radiation Medicine, Academy of Medical Science, Kyiv, Ukraine

Abstract
Background: Hypothyroidism is the most common thyroid abnormality in patients treated with high doses of iodine-131 (¹³¹I) . Data on risk of hypothyroidism from low to moderate ¹³¹I thyroid doses are limited and inconsistent.

Objective: This study was conducted to quantify the risk of hypothyroidism prevalence in relation to ¹³¹I doses received because of the Chornobyl accident.

Methods: This is a cross-sectional (1998–2000) screening study of thyroid diseases in a cohort of 11,853 individuals < 18 years of age at the time of the accident, with individual thyroid radioactivity measurements taken within 2 months of the accident. We measured thyroid-stimulating hormone (TSH) , free thyroxine, and antibodies to thyroid peroxidase (ATPO) in serum.

Results: Mean age at examination of the analysis cohort was 21.6 years (range, 12.2–32.5 years) , with 49% females. Mean ¹³¹I thyroid dose was 0.79 Gy (range, 0–40.7 Gy) . There were 719 cases with hypothyroidism (TSH > 4 mIU/L) , including 14 with overt hypothyroidism. We found a significant, small association between ¹³¹I thyroid doses and prevalent hypothyroidism, with the excess odds ratio (EOR) per gray of 0.10 (95% confidence interval, 0.03–0.21) . EOR per gray was higher in individuals with ATPO ≤ 60 U/mL compared with individuals with ATPO > 60 U/mL (p < 0.001) .

Conclusions: This is the first study to find a significant relationship between prevalence of hypothyroidism and individual ¹³¹I thyroid doses due to environmental exposure. The radiation increase in hypothyroidism was small (10% per Gy) and limited largely to subclinical hypothyroidism. Prospective data are needed to evaluate the dynamics of radiation-related hypothyroidism and clarify the role of antithyroid antibodies.

Key words: Chernobyl nuclear accident, Chornobyl, dose–response relationship, hypothyroidism, ionizing radiation. Environ Health Perspect 117:745–750 (2009) . doi:10.1289/ehp.0800184 available via http://dx.doi.org/ [Online 15 December 2008]

Address correspondence to A. Brenner, Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics, National Cancer Institute, NIH, MS 7238, 6120 Executive Blvd., Bethesda, MD 20892-7238 USA. Telephone: (301) 402-8680. Fax: (301) 402-0207. E-mail: brennera@mail.nih.gov

J.R. is now deceased.

We thank the Louise Hamilton Kyiv Data Management Center of the University of Illinois at Chicago, supported in part by the NIH Fogarty International Center, and its head, O. Zvinchuk, for database management ; J.H. Lubin (NCI) for suggestions on statistical analyses ; and the late O. Epshtein (Research Institute of Endocrinology and Metabolism, Kyiv, Ukraine) and the late D.J. Fink (Columbia University) for laboratory expertise and support. We owe special acknowledgments to the late G.W. Beebe and G.R. Howe, who provided overall guidance and inspiration for the Ukrainian–American Thyroid Study.

This research was supported by the Intramural Research Program of the U.S. National Institutes of Health, the U.S. National Cancer Institute, and the U.S. Department of Energy. The U.S. Nuclear Regulatory Commission provided the initial funds for purchase of equipment.

The funding agencies had no influence on study design, conduct, or reporting.

The authors declare they have no competing financial interests.

Received 12 September 2008 ; accepted 15 December 2008.