Iodine nutrition and diffuse euthyroid goiter for the cohort members of Ukraine-U.S.A. thyroid project among a population affected by the Chornobyl catastrophe

Full text: The most significant consequence of the Chornobyl catastrophe for the health of the exposed population is the adverse effect of radioiodine on the thyroid. In addition, the level of stable iodine in the diet can also influence the development of thyroid pathology, including thyroid cancer. Therefore, in a Ukraine-USA thyroid project, iodine status of study subjects was also evaluated. The most meaningful indexes of iodine status, recommended by WHO, are the concentration of iodine in urine and frequency of goiter. The Ukraine-USA Thyroid Project carried out screening examinations of the thyroid gland every two years on a cohort of approximately 13,000 individuals who were less than age 18 at the time of the accident. This report focuses on the first two screening cycles, conducted in 1998-2000 and 2001-2003. In addition to measurements of iodine in urine, the thyroid gland was examined by palpation and by ultrasound. Cohort members who contributed urine samples included, in the 1st and 2nd cycles respectively, from the Kyiv area, 1691 and 1661, Zhytomyr, 3297 and 3095, Chernihiv, 6119 and 6102 areas and in Kyiv City, 810 and 839. In total,general complication during the 1st cycle 11937 specimens of urine were collected and analyzed, and in the 2nd cycle 11732. Intake of stable iodine was assessed by questionnaire, which included items about the consumption of products rich in an iodine, and also special preparations containing this element. The results showed that during the first cycle the highest mean level of iodine excretion was observed in the districts of the Kiev area of 72,1 1,8 g/L; the median level was 55.7 g/L. Although high in relative terms, these values are still indicative of a degree of iodine deficit. Only 20% of iodine excretions were higher than 100 g/L, widely considered to be the norm. Indexes of median iodine excretion indicative of moderate to severe iodine insufficiency, were observed also in Chernihiv. The most serious problem was in Narodychi and Ovruch districts, where only about 8% of members of the cohort had a normal consumption of iodine. The results show that in general iodine levels are higher in towns than in rural areas. The questionnaire analysis of the 1st cycle shows that in the period of 1998-2000 the study population in general did not consume iodine preparations (iodine salt, multivitamins containing an iodine, medical preparations with an iodine: antistrumin, iodide of potassium, thyroxin) or consumed them extremely rarely. On the whole for all settlements the frequency of adopting the indicated preparations was only 5,4%, suggesting that these foods and preparations had little impact on the iodine status of the populations whether in cities or rural localities. Variation in the level of iodine concentrations in different regions was also observed in the second screening cycle. The highest levels were observed in Kiev, where the mean level of urinary iodine excretion was 101 3,3 g/L, and the median, 75,7 g/L. In other regions, iodine status was noticeably worse, except for the Kiev area, where 30,7% had levels indicative of iodine sufficiency. As in the first screening cycle, urinary iodine concentrations were higher in cities than in rural areas. Comparison of results of iodine excretion in the first and second cycle of screening showed a substantial increase in concentration levels; the consumption of products containing iodine also increased. On the whole, territories contaminated by the Chornobyl accident are areas with iodine deficits of mild to moderate degree. The results of determination of prevalence of diffuse goiter confirm the presence of iodine deficiency in regions of residence of the cohort members. The prevalence of diffuse goiter according to data of 1st and 2nd cycles was about 20%. This situation has as yet uncertain consequences for thyroid pathology and for effects of radiation