Iodine Nutrition and the Risk from Radioactive Iodine: A Workshop Report in the Chernobyl Long-Term Follow-Up Study

Abstract

The major fallout of radionuclides from the nuclear power station accident at Chernobyl on 26 April, 1986, occurred in regions of Ukraine and Belarus that are believed to be moderately deficient in dietary iodine. On 17 November, 2000, in conjunction with the Ukraine-Belarus-USA study of developing thyroid disease in a cohort of individuals exposed as children, a workshop was held to review what is known about iodine nutrition in the region, how this might influence the risk of thyroid tumor formation from radioiodine, and whether and how iodine nutrition should be monitored in this long-term project. This report is a summary of the workshop proceedings. Although no precise information about iodine intake in 1986 was found, the prevalence of mild goiter in the region's children suggested iodine deficiency and urinary iodine measurements begun in 1990 indicated that mild to moderate deficiency existed. Increased thyroid iodine uptake and increased thyroid size in 1986 resulting from iodine deficiency would have had counteracting influence on the thyroid radiation dose and knowledge of these parameters is required for dose reconstruction. More problematic is the possible role of iodine deficiency in the years following the accident. Theoretically, the resulting increase in thyroid cellular activity might increase the risk of tumorigenesis but experimental or clinical evidence supporting this hypothesis is meager or absent. Despite this limitation it was considered important to monitor iodine nutrition in the cohort subjects in relation to their place of residence and over time. Methods to accomplish this were discussed.

Inhibitory effect of low-dose inorganic iodine on thyroidal radioactive iodine uptake in healthy Japanese adults

“…Iodine nutritional status at the time of exposure to radioactive iodine strongly affects the thyroid radiation dose [6], and it is also reported that iodine deficiency increases the risk of 131 I-related thyroid cancer [7]. Japan is regarded as an iodine sufficient country [8], and there are still controversies on the timing, dose, and length of administration of KI to block the uptake of radioiodine by the thyroid.…”

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

“…Firm data are lacking on iodine status in regions of Belarus during the year of the Chornobyl accident (2). An historical report from Belarusian scientists describes an increasing rate of diffuse goiter in the decades from 1970 to 1990 but does not give a specific figure for 1986 (8).…”

Dietary iodine intake, thyroid diseases and the prevalence of papillary carcinoma (PTC)

“…External radiation to the thyroid increases risk of thyroid cancer, particularly when the radiation occurs in children or adolescents [12][13][14][15][16][17][18][19][20].The Chernobyl nuclear accident in 1986 exposed population of Belarus, Ukraine, and the Russian Federation to internal radiation from radioactive iodines deposited in the thyroid, resulting in sharp increase in pediatric and adolescent thyroid cancer [18]. About 60% of the Belarusian thyroid cancer and 30% of the Ukrainian cases, mainly PTC, were identified about 20 years after the accident [21].…”

“…About 60% of the Belarusian thyroid cancer and 30% of the Ukrainian cases, mainly PTC, were identified about 20 years after the accident [21]. Historically, the areas exposed to Chernobyl fallout were affected by varying degrees of past iodine deficiency [22].Chronic iodine deficiency increases thyroidal clearance of plasma iodine, increases thyroid blood flow and thyrocyte proliferation, and increases thyroid size, all of which may increase thyroid uptake of ingested radioiodines, also thereby increasing vulnerability of thyroid to the accumulated radioiodines [15,23].A history of goiter was associated with the risk of thyroid cancer (OR 2.19),but the study had limited due to a small number of cancer cases (n=45) [17,20].…”