Evaluation of the effectiveness of iodine prophylaxis in Poland based on over 20 years of observations of iodine supply in school-aged children in the central region of the country

Introduction Due to the mild-to-moderate iodine deficiency in Poland, in 1997 iodine prophylaxis based on obligatory salt iodization was introduced. We attempted to evaluate the effectiveness of such prophylaxis, based on over 20 years of observations of iodine supply in school-aged children in Opoczno district (Central Poland). Material and methods A group of 603 children (316 girls and 287 boys), aged 6–14, was examined at 4 time points: in the years 1994, 1999, 2010 and 2016. The children were tested for urine iodine concentration (UIC) and in each child the thyroid volume was measured ultrasonographically. Results The median UIC in 1994 (45.5 μg/l) indicated moderate iodine deficiency, while after introducing prophylaxis it corresponded to adequate values (1999 – 101.1 μg/l, 2010 – 100.6 μg/l, 2016 – 288.3 μg/l); however, the last value was higher than the previous two. The thyroid size, assessed by ultrasonography and presented as volume/body surface area (V/BSA), in 1994 was 6.55 × 10–6 m; this value was higher than at other time points (2.73 × 10–6 m in 1999, 2.73 × 10–6 m in 2010, and 2.70 × 10–6 m in 2016). Conclusions Iodine prophylaxis has proved effective in eliminating iodine deficiency. In recent years, the diversification of iodine sources, despite the reduction of salt consumption, has led to an increase in median UIC to values close to the upper limit of UIC, accepted as normal. Further increase in iodine supply may be unfavourable for health; therefore constant monitoring of iodine prophylaxis is required.