Prevalence of Hyperthyroidism after Exposure during Childhood or Adolescence to Radioiodines from the Chornobyl Nuclear Accident: Dose–Response Results from the Ukrainian-American Cohort Study

Abstract

Relatively few data are available on the prevalence of hyperthyroidism (TSH concentrations of < 0.3 mIU/L, with normal or elevated concentrations of free T4) in individuals exposed to radioiodines at low levels. The accident at the Chornobyl (Chernobyl) nuclear plant in Ukraine on April 26, 1986 exposed large numbers of residents to radioactive fallout, principally to iodine-131 (I-131) (mean and median doses = 0.6 Gray (Gy) and 0.2 Gy). We investigated the relationship of I-131 and prevalent hyperthyroidism among 11,853 individuals exposed as children or adolescents in Ukraine who underwent an in-depth, standardized thyroid gland screening examination 12–14 years later. Radioactivity measurements taken shortly after the accident were available for all subjects and were used to estimate individual thyroid doses. We identified 76 cases of hyperthyroidism (11 overt, 65 subclinical). Using logistic regression, we tested a variety of continuous risk models and conducted categorical analyses for all subjects combined and for females (53 cases, n=5,767) and males (23 cases, n=6,086) separately, but found no convincing evidence of a dose response relationship between I-131 and hyperthyroidism. There was some suggestion of elevated risk among females in an analysis based on a dichotomous dose model with a threshold of 0.5 Gy chosen empirically (OR=1.86, P=0.06), but the statistical significance level was reduced (P=0.13) in a formal analysis with an estimated threshold. In summary, after a thorough exploration of the data, we found no statistically significant dose response relationship between individual I-131 thyroid doses and prevalent hyperthyroidism.

Measures of Thyroid Function among Belarusian Children and Adolescents Exposed to Iodine-131 from the Accident at the Chernobyl Nuclear Plant

“…Similarly, no evidence of a positive association between 131 I dose and hyperthyroidism or AIT was found in the Ukrainian cohort (Hatch et al 2010; Tronko et al 2006a). However, lack of a positive association between 131 I and prevalence of ATPO in Belarus contrasts with significant positive nonlinear association with 131 I observed in Ukraine (Tronko et al 2006a).…”

“…In a screening study among 12,000 subjects in Ukraine with doses estimated from individual measurements of thyroid radioactivity, significant associations were found between 131 I thyroid dose (mean dose of 0.79 Gy) and prevalence of subclinical hypothyroidism (Ostroumova et al 2009) and antibodies to thyroperoxidase (ATPO) (Tronko et al 2006a), but not autoimmune thyroiditis (AIT) (Tronko et al 2006a) or hyperthyroidism (Hatch et al 2010). …”

Radiation-related thyroid autoimmunity and dysfunction

“… Radiation dose # subjects Interval between time of accident and study (years) Results in the exposed subjects Ito [ 26 ] various degrees of radioactive contamination 55 054 5–7 an increase in the incidence of chronic thyroiditis Vykhovanets [ 27 ] 131 I thyroid dose of <1.0–>2.0 mSv 29 7–8 an increase in positivity of anti-thyroglobulin antibodies Pacini [ 28 ] average Cs of 5.4 Ci/km 2 287 6–8 an increase in positivity of anti-thyroglobulin/TPO antibodies Vermiglio [ 29 ] average Cs of 37–185 GBq/km 2 143 6–8 an increase in positivity of anti-thyroglobulin/TPO antibodies Pacini [ 30 ] various degrees of radioactive contamination in Belarus 171 thyroid cancer cases 0–10 an increase in chronic thyroiditis and positivity of anti-TPO antibodies Ivanov [ 31 ] 0.132 ± 0.45 (mean + S.D.) Gy 11–13 no significant relationship between radiation dose and the prevalence of chronic thyroiditis Stezhko [ 33 ], Hatch [ 34 ], Ostroumova [ 35 ] and Tronko [ 36 ] (Ukrainian–American Cohort Study of Thyroid Cancer and Other Thyroid Diseases) average 131 I thyroid dose of 0.79 (ranged, 0–40.7) Gy ~12 000 12–14 …”

Chronic exposure of adult, postnatal and in utero rat models to low-dose 137Cesium: impact on circulating biomarkers

“…Studies show a link between 131 Iodine contamination and these diseases [52, 53], although the possible role of additional radionuclides (including 137 Cs) and external radiation in the induction of these diseases remains uncertain. To study thyroid function thoroughly, we measured TSH, which is considered the most sensitive marker for this purpose, together with the free T3/T4 ratio [54].…”