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Environ Health Perspect. 2009 May;117(5):745-50. doi: 10.1289/ehp.0800184. Epub 2008 Dec 15.

Subclinical hypothyroidism after radioiodine exposure: Ukrainian-American cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident (1998-2000).

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  • 1Radiation Epidemiology Branch, Division of Cancer Epidemiology and Genetics National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland 20892-7238, USA.



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.


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


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.


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 (131)I 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 < or = 60 U/mL compared with individuals with ATPO > 60 U/mL (p < 0.001).


This is the first study to find a significant relationship between prevalence of hypothyroidism and individual (131)I 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.


Chernobyl nuclear accident; Chornobyl; dose–response relationship; hypothyroidism; ionizing radiation

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