Background: Thyroid dysfunction after exposure to low or moderate doses of radioactive iodine-131 (131I) at a young age is a public health concern. However, quantitative data are sparse concerning 131I-related risk of these common diseases.Objective: Our goal was to assess the prevalence of thyroid dysfunction in association with 131I exposure during childhood (≤ 18 years) due to fallout from the Chernobyl accident.Methods: We conducted a cross-sectional analysis of hypothyroidism, hyperthyroidism, autoimmune thyroiditis (AIT), serum concentrations of thyroid-stimulating hormone (TSH), and autoantibodies to thyroperoxidase (ATPO) in relation to measurement-based 131I dose estimates in a Belarusian cohort of 10,827 individuals screened for various thyroid diseases.Results: Mean age at exposure (± SD) was 8.2 ± 5.0 years. Mean (median) estimated 131I thyroid dose was 0.54 (0.23) Gy (range, 0.001–26.6 Gy). We found significant positive associations of 131I dose with hypothyroidism (mainly subclinical and antibody-negative) and serum TSH concentration. The excess odds ratio per 1 Gy for hypothyroidism was 0.34 (95% CI: 0.15, 0.62) and varied significantly by age at exposure and at examination, presence of goiter, and urban/rural residency. We found no evidence of positive associations with antibody-positive hypothyroidism, hyperthyroidism, AIT, or elevated ATPO.Conclusions: The association between 131I dose and hypothyroidism in the Belarusian cohort is consistent with that previously reported for a Ukrainian cohort and strengthens evidence of the effect of environmental 131I exposure during childhood on hypothyroidism, but not other thyroid outcomes.

Background Recent studies of children and adolescents exposed to radioactive iodine-131 (I-131) after the 1986 Chernobyl nuclear accident in Ukraine showed significant dose-related increase in the risk of thyroid cancer, but the association of radiation doses with tumor histological and morphological features is not clear. Methods A cohort of 11,664 individuals in Belarus ≤18 years at the time of the accident underwent three cycles of thyroid screening in 1997-2008. I-131 thyroid doses were estimated from individual thyroid activity measurements taken within two months after the accident and dosimetric data from questionnaires. Demographic, clinical and pathological characteristics of thyroid cancer cases were analyzed using one-way analysis of variance, chi-square or Fisher's exact tests, and logistic regression. Results As a result of screening, 158 thyroid cancers were identified. The majority of cases had T1a and T1b tumors (93.7%), with many regional N1 (60.6%) but few distant M1 (<1%) metastases. Higher I-131 doses were associated with higher frequency of solid or diffuse sclerosing variants of thyroid cancer (P<0.01) and histological features of cancer aggressiveness, such as lymphatic vessel invasion, intrathyroidal infiltration, and multifocality (all P<0.03). Latency was not correlated with radiation dose. Fifty-two cases of self-reported thyroid cancers diagnosed prior to 1997 were younger at the time of the accident and had a higher percentage of solid variant cancers compared to screening-detected cases (all P<0.0001). Conclusions I-131 thyroid radiation doses were associated with significantly higher frequency of solid or diffuse sclerosing variants of thyroid cancer and various features of tumor aggressiveness.

SUMMARY Objective Serum thyroglobulin (Tg) has been associated with a number of thyroid disorders and has been proposed as an indicator of iodine deficiency in a population. However, few studies have addressed the epidemiology of Tg in a population-based setting or in the context of exposure to radioactive iodine-131 (I-131). Our objective was to evaluate baseline levels of Tg in relation to socio-demographic characteristics, iodine status, and thyroid function for individuals exposed to I-131. Design A population-based cohort assembled in Belarus following the Chornobyl accident provided demographic factors, clinical data, and physiological measurements. Participants Our analytic sample included 10,344 subjects of whom 7,890 had no thyroid disease and 2,454 had evidence of structural or functional thyroid abnormality. Measurements Standardized assays were used to measure serum Tg, urinary iodine, TSH, and antibodies to Tg and thyroid peroxidase. Ultrasound was used to assess the presence of nodules and estimate thyroid volume. Results In the fully adjusted model, percent change in Tg was significantly increased among females, smokers, and subjects of older age and Tg increased with decreasing urinary iodine concentration, increasing serum TSH and increasing thyroid volume (p-values for trend < 0.0001), and presence of thyroid nodules (p < 0.05). We found a complex interaction between region of residence, rural/urban living, presence/absence of thyroid abnormalities, and serum Tg (p < 0.0001). Conclusions In residents of Belarus, serum Tg is significantly related to presence of thyroid abnormalities as well as indicators of thyroid function and iodine deficiency and, therefore, could be used to characterize the iodine status and thyroid function of individuals in the context of epidemiological study.

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