A 40 VOLUME 122 | NUMBER 2 | February 2014 • Environmental Health Perspectives Perspectives | Correspondence Perspectives | Correspondence All EHP content is accessible to individuals with disabilities. Fully accessible (Section 508–compliant) HTML versions of these articles are available at http://dx.doi.org/10.1289/ehp.1307737 and http://dx.doi.org/10.1289/ehp.1307737R. The correspondence section is a public forum and, as such, is not peer-reviewed. EHP is not responsible for the accuracy, currency, or reliability of personal opinion expressed herein; it is the sole responsibility of the authors. EHP neither endorses nor disputes their published commentary. Iodine-131 and Thyroid Function http://dx.doi.org/10.1289/ehp.1307737 Ostroumova et al. (2013) reported an associa- tion between iodine-131 ( 131 I) dose and hypothyroidism in the Belarusian cohort, a cohort of individuals exposed to 131 I from fall- out of the Chernobyl accident when they were ≤ 18 years of age. Ostroumova et al. also exam- ined other thyroid outcomes: hyperthyroidism, autoimmune thyroiditis, serum concentrations of thyroid-stimulating hormone, and auto- antibodies to thyroperoxidase. It may not be appropriate to include participants with other thyroid outcomes in the analysis because those thyroid out- comes could be indirectly associated with exposure. Chernobyl is in an iodine-deicient area (Ishigaki et al. 2001), and the preva- lence of goiters among children ≤ 18 years of age has been reported at > 15% in this area (Hatch et al. 2011). Is high prevalence of goiters in the area caused by normal iodine deiciency or by the 131 I? If the goiters were caused by 131 I, the relationship between the 131 I and hypothyroidism is still unclear, even though Ostroumova et al. (2013) stratiied the data according to the presence of goiters. Hypothyroidism can also cause goiters (Wilkins et al. 1954); thus, goiter is just a serious hypothyroidism. hat could be the explanation for the higher excess odds ratio in the group with goiter compared with the group without goiter shown in Table 3 of Ostroumova et al. (2013). It would have been better for Ostroumova et al. to perform a stratified analysis on the relationship between 131 I and hypothyroidism based on the normal iodine level of the individual rather than the presence of goiter. Ostroumova et al. (2013) also claimed that the thyroid radioactivity of individuals from the Belarus cohort was based on a pre- vious study (Stezhko et al. 2004). However, Stezhko et al. (2004) did not provide the details of the individual radioactive iodine measurement. Were the original radioactive iodine measurements generated from a for- mula or modeled based on food intake or soil contamination, or was the 131 I exposure level actually measured for each individual? The answer to this question is necessary because the two methods have diferent credibility. In addition, the exposure described by Stezhko et al. (2004) included 131 I as well as other radioactive isotopes of iodine, not 131 I alone. I would like to know whether Ostroumova et al. (2013) separated 131 I from other radio- active iodine isotopes. Cesium-137 should also be considered as a potential confounder in the relationship between 131 I and hypothyroidism. The author declares no actual or potential competing financial interests. Wenjie Sun Global Health and Environmental Sciences, Tulane University School of Public Health and Tropical Medicine, New Orleans, Louisiana, USA E-mail: wsun3@tulane.edu REFERENCES Hatch M, Polyanskaya O, McConnell R, Gong Z, Drozdovitch V, Rozhko A, et al. 2011. Urinary iodine and goiter prevalence in Belarus: experience of the Belarus–American cohort study of thyroid cancer and other thyroid diseases following the Chornobyl nuclear accident. Thyroid 21:429–437. Ishigaki K, Namba H, Takamura N, Saiwai H, Parshin V, Ohashi T, et al. 2001. Urinary iodine levels and thyroid diseases in children; comparison between Nagasaki and Chernobyl. Endocr J 48:591–595. Ostroumova E, Rozhko A, Hatch M, Furukawa K, Polyanskaya O, McConnell RJ, et al. 2013. Measures of thyroid function among Belarusian children and adolescents exposed to iodine-131 from the accident at the Chernobyl nuclear plant. Environ Health Perspect 121:865–871; doi:10.1289/ ehp.1205783. Stezhko VA, Buglova EE, Danilova LI, Drozd VM, Krysenko NA, Lesnikova NR, et al. 2004. A cohort study of thyroid cancer and other thyroid diseases after the Chornobyl accident: objectives, design and methods. Radiat Res 161:481–492. Wilkins L, Clayton GW, Berthrong M. 1954. Development of goiters in cretins without iodine deficiency: hypo- thyroidism due to apparent inability of the thyroid gland to synthesize hormone. Pediatrics 13:235–246. Iodine-131 and Thyroid Function: Ostroumova et al. Respond http://dx.doi.org/10.1289/ehp.1307737R Sun’s comments about the relationship between iodine-131 ( 131 I), hypothyroidism, and simple diffuse goiter suggest a mis- understanding of our study findings. We reported a signiicantly higher—rather than lower—radiation-associated risk of hypo- thyroidism among study participants without goiter than in the participants with goiter (Ostroumova et al. 2013). Specifically, the excess odds ratio (EOR) per Gray of 131 I thy- roid dose was 0.50 [95% conidence inter- val (CI): 0.24, 0.90] in participants without goiter and 0.04 (95% CI: –0.09, 0.32) in those with goiter. We also reported a lack of significant variation of EOR per Gray for hypothyroidism by levels of urinary iodine (p = 0.23), although in the discussion we noted that iodine concentration in spot urine samples, unlike presence of diffuse goiter, relects current levels of iodine intake and is subject to high within-individual variability. he territories of Belarus were known to be iodine deicient before the Chernobyl accident; in the Soviet Union there was a system of iodine prophylaxis that was discontinued by the mid-1980s (Kholodova and Fedorova 1992). In 1995–1998, ive of the six Belarus regions were classiied as having moderate iodine dei- ciency, whereas the Gomel region, most heav- ily contaminated with 131 I, was classified as having mild iodine deficiency partly due to some iodine supplementation in this area after the Chernobyl accident (Arinchin et al. 2000). High prevalence of difuse goiter detected by ultrasound in children and adolescents in the relatively uncontaminated Brest region (27.8%) and low prevalence in the heavily contami- nated Gomel region (5.6%) (Arinchin et al. 2000) support the idea that these diferences are attributed to diferent intake of dietary iodine and not to 131 I exposure. Moreover, there is little evidence of a dose–response association between thyroid exposure and simple diffuse goiter in other radiation-exposed cohorts (Ron and Brenner 2010). As we described in the “Materials and Methods” of our article (Ostroumova et al. 2013), availability of individual direct measure- ments of thyroid radioactivity served as a key criterion for inclusion into the study. All study participants had direct measurements of thyroid radioactivity performed within 2 months after the accident. In the methods for dosimetry, we cited the article by Drozdovitch et al. (2013), in which dose reconstruction methods were described in detail. We also noted that intake of 131 I on average accounted for about 95% of the estimated thyroid dose, whereas the contribution of other short-lived radioiodines, external exposures, and internal exposure from cesium-137 and cesium-134 was minor (Bouville et al. 2007). We appreciate Sun’s interest in our study and hope our response is useful. The authors declare that they have no actual or potential competing financial interests. Evgenia Ostroumova, 1 Alexander Rozhko, 2 Maureen Hatch, 1 Kyoji Furukawa, 3 Olga Polyanskaya, 2 Robert J. McConnell, 4 Eldar Nadyrov, 2 Sergey Petrenko, 5 George Romanov, 2 Vasilina Yauseyenka, 2 Vladimir Drozdovitch, 1 Viktor Minenko, 6 Alexander Prokopovich, 2 Irina Savasteeva, 2 Lydia B. Zablotska, 7 Kiyohiko Mabuchi, 1 and Alina V. Brenner 1 1 Division of Cancer Epidemiology and Genetics, National Cancer Institute, National Institutes of Health, Department of Health and Human Services, Bethesda, Maryland, USA; 2 The Republican Research Center for Radiation Medicine and Human Ecology, Gomel, Belarus; 3 Department of Statistics, Radiation Effects Research Foundation, Hiroshima, Japan; 4 The Thyroid Center, Columbia University, New York, New York, USA; 5 Department of Anthropoecology and Epidemiology, International Sakharov Environmental University, Minsk, Belarus; 6 Belarusian Medical Academy of Post- Graduate Education, Minsk, Belarus; 7 Department of Epidemiology and Biostatistics, University of California, San Francisco, San Francisco, California, USA E-mail: ostroume@mail.nih.gov