Academic journal article Environmental Health Perspectives

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

Academic journal article Environmental Health Perspectives

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

Article excerpt

The most severe accident in the history of nuclear industry occurred on 26 April 1986, at the Chernobyl nuclear power plant located in Ukraine, about 10 km south of the border with Belarus. The radioactive fallout contained short-lived, mainly radioiodines, and long-lived radionuclides such as cesium-137 ([sup.137]Cs). Overall, 1,760 petabecquerel (PBq = [10.sup.15] Bq) of iodine-131 ([sup.131]I) and 85 PBq of [sup.137]Cs were released into the environment [United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) 2010].

Persons [less than or equal to] 18 years of age at the time of the accident received substantial thyroid doses of [sup.131]I due to consumption of contaminated milk and dairy products and relatively small size of the thyroid gland. An association has been established between [sup.131]I exposure during childhood and thyroid cancer risk in Ukraine, Belarus, and the Bryansk region of the Russian Federation (Brenner et al. 2011; Cardis et al. 2005; Kopecky et al. 2006; Tronko et al. 2006b; Zablotska et al. 2011). Two decades after the accident there is no evidence of a decline in radiation-related risk of thyroid cancer (Brenner et al. 2011).

Post-Chernobyl consequences of childhood [sup.131]I exposure on thyroid function are less clear, but diseases related to thyroid function (e.g., hypothyroidism, hyperthyroidism) are more common than thyroid cancer and could result in substantial morbidity among those exposed. Some earlier studies reported an increase in thyroid-stimulating hormone (TSH) levels and the prevalence of juvenile hypothyroidism among children exposed to [sup.131]I following Chernobyl (Goldsmith et al. 1999; Quastel et al. 1997; Vykhovanets et al. 1997), but other studies did not (Agate et al. 2008; Kasatkina et al. 1997; Pacini et al. 1998; Vermiglio et al. 1999). An increased prevalence of thyroid autoimmunity has been reported (Kasatkina et al. 1997; Pacini et al. 1998; Vermiglio et al. 1999), although it seemed to be transient with no long-term effect on thyroid function (Agate et al. 2008). Most studies published to date, except for the cohort study in Ukraine described below, were limited in size or lacked individual dose estimates.

In a screening study among 12,000 subjects in Ukraine with doses estimated from individual measurements of thyroid radioactivity, significant associations were found between [sup.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).

To extend findings from the Ukrainian cohort, we evaluated functional thyroid outcomes in relation to individual [sup.131]I thyroid doses in a comparable cohort of exposed children and adolescents from Belarus who were screened for thyroid cancer and other thyroid diseases. The methods used to estimate thyroid doses and to screen for thyroid diseases in Belarus and Ukraine were similar (Stezhko et al. 2004).

Methods

Study population. The Belarus cohort consists of individuals who were [less than or equal to] 18 years of age on 26 April 1986 and had their thyroid radioactivity measured within 2 months of the accident. Study design and methods have been described in detail by Stezhko et al. (2004). The study protocol called for a standardized, in-depth thyroid screening examination every 2 years. In total, 38,543 eligible individuals were identified. Of these, 16,213 were traced through address bureaus, military registration offices, departments of education and public health, and medical establishments, and sent invitation letters explaining the study. The present analysis is based on the data collected from the 11,970 traceable cohort members who attended the first screening examination conducted between 1996 and 2003. Of 11,970 individuals examined in the first screening cycle, we sequentially excluded from the analytic cohort 1,143 participants because of incorrect identification (n = 20); noneligible age (n = 114); inadequate dose estimates (n = 104); self-reported history of any thyroid disease before screening examination including, for example, nodular or diffuse goiter, thyroiditis, hypo- and hyperthyroidism (n = 542), or benign thyroid surgery (n = 58) or thyroid hormone intake (n = 168); lack of TSH measurements (n = 59) or TSH measured using AxSYM method (Abbott Laboratories. …

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