[Geographic differences in iodine supply in the Silesia terrain in relation to thyroid cancer risk]

Risk factors associated with differentiated thyroid carcinoma depend on its histotype. Follicular carcinoma is described as a predominant type in the areas with iodine deficiency, in opposite to papillary thyroid cancer. The incidence of thyroid cancer and its histotypes varies considerably throughout Silesia (data obtained from the Institute of Oncology Cancer Register, Gliwice). The factors responsible for these differences are unknown. The aim of our study was to evaluate the present iodine supply in Silesia region and to relate it to the incidence of the various histotypes of thyroid carcinoma. Urinary iodine excretion observed in 7-11 year-old-children was used as a parameter of iodine supply and measured in the group of 1037 school children in sixteen localities, equally dispersed throughout Silesia. Urine samples were obtained to measure iodine concentration by the modified Sandell-Kolthoff's catalytic method. Mean incidence rates of papillary and follicular thyroid carcinoma were calculated for regions of Silesia by averaging the rates of the communities in each region. Despite the intensive iodine prophylaxis the persistent symptoms of iodine deficiency were observed. There were significant differences in children's ioduria among investigated regions. The percentage of low ioduria (lower then 100 micrograms/l) varied from 35.7% to 87.7%. We observed no correlation between age-adjusted rates for histotypes of thyroid carcinoma and the percentage of urine iodine below 100 micrograms/l, which served as an estimation of iodine deficiency. Our study indicates that Silesia is still an area of moderate iodine deficiency. We were unable to explain the factors responsible for the observed differences in the incidence rates of papillary and follicular thyroid carcinoma.