The aim of the study was to demonstrate the effectiveness of iodine prophylaxis conducted in Poland. Results of the survey carried out in 1999 showed that iodine prophylaxis introduced in 1997 had proved to be effective [16, 17].
A significant decrease in goitre incidence and thyroid size was observed, together with the increase in iodine excretion. The obtained results are consistent with other studies assessing the effectiveness of implemented iodine prophylaxis. Based on the studies from that period, Poland was classified as a country in which there was no iodine deficiency .
Eleven years later (2010), children from the same school were re-examined in order to follow the efficacy of conducted prophylaxis.
The value of mean and median of UICs has not changed, however this does not mean that there have been no changes. The analysis of UICs distribution shows that in 1999 the value scatter was much bigger than in 2010 (Figure 1). The percentage of children, in whom UIC was less than 50 μg/L decreased from 12.6 to 7.1% (Figure 2). Having analyzed the UICs distribution, it was found that the percentage of children with lower values of iodine concentration had decreased. Data demonstrate not only the effectiveness of iodine prophylaxis but also more even, homogenous iodine intake in comparison to year 1999. The greater uniformity of examined sample translates into easier grasping of statistical significances. The correlation between thyroid size and UICs value was observed only in 2010 (Pearson’s correlation coefficient was −0.165 with p=0.031). Such correlation was not seen in previous years. Moreover, in 2010 it was found that V/BSA ratio value was bigger in girls than in boys (p=0.013), which also indirectly points to greater uniformity of the examined population.
It is to be emphasized that the obtained values oscillate practically around lower optimal values. The optimal values of median of UICs in school-aged children are thought to be in the range between 100 and 200 μg/L.
The evaluation of UICs in school-aged children proved to be efficient reflection of iodine dietary intake. However, the values of median and mean are not the only parameters that reflect the iodine dietary intake. Analysis of data distribution, as well as analysis of percentage of children with iodine concentrations below normal values, is also very important.
It seems that the biggest problem is to define the reference values of thyroid volume, i.e. the values above which one can recognize thyroid enlargement – goitre. In 1999, when we were analyzing the obtained data, the reference values proposed by Delange et al. were in force – using these standards – the frequency of goitre was 37.5% (27.8% in girls, 48.0% in boys) in 1994, and 1.4% (1.0% in girls and 1.9% in boys) in 1999 . Despite the fact that the reference values by Delange were considered to be too liberal, the degree of goitre severity, assessed according to them, correlated well with the degree of iodine deficiency assessed based on UIC.
In 2004, the reference values by Zimmermann et al. were presented and they were applied in our study. Having analyzed the obtained results, it was found that there had been a significant decrease in goitre incidence in 1999 and 2010 in comparison to 1994, taking into account both age and sex, as well as body surface area and sex. No differences in the goitre incidence between year 1999 and 2010 or between the group of girls and boys were found. However, the analysis of the obtained data may encounter common sense objections.
We are aware that before introduction of the iodine prophylaxis, there was an endemicity of goitre to moderate or average extent (20-40%); these data correlated with the iodine concentrations in urine samples. However, it is hard to believe that iodine deficiency was so large that it led to the goitre occurrence with the frequency of 90%. The evaluation of goitre incidence after the introduction of the iodine prophylaxis is also doubtful, as the frequency of goitre occurrence is still so high that it reaches the level of goitre endemicity (15-18%). This is in conflict with the values of UIC. We should expect the goitre incidence oscillating around the upper limit of normal values (ap. 5%). Therefore, one can assume that there are no reliable norms, to which the obtained results can be compared. Taking into consideration the fact that Delange’s and Zimmermann’s reference values were not the only ones – earlier quite rigorous reference values were proposed by Gutekunst et Martin-Teichert  – one can say that the reliable assessment of goitre incidence on the basis of currently available reference values is impossible. Polish reference values established by Szybinski et al. are also not representative as they were developed only with regard to age (not BSA); what is more, the study subjects were highly selected and did not reflect general pediatric population .
However, it does not mean, that the analysis of obtained results is useless. We have suggested comparing the thyroid volume measured by ultrasound to the child’s body surface area. The idea of such comparison is similar to the historic comparison of normal thyroid lobe to the examined person thumb .
The advantage of such comparison was the fact that the original data and not the interpreted ones were analyzed (thyroid enlarged vs. not enlarged). Moreover, data analyzed in such a manner are continuous data, which is especially important during childhood. In the case of the reference values, the rule of ranges enforces us to round the obtained results, which causes even more relativism. Furthermore, it is difficult to accept the reference values developed in population of children living far from Poland. When analyzing such results, one must be aware that in a particular site other goitrogenic factors might influence the population, the ethnic diversity should be also taken into account. All these issues make it very difficult to define universal reference values, which would be reliable.
The values of V/BSA ratio proves that after the implementation of iodine prophylaxis, the thyroid volume decreased significantly (Figure 5). Analysis of the obtained values between year 1999 and 2010 showed that V/BSA ratio value was higher in girls than in boys (especially high values were observed in girls aged 7–10).
Therefore, analysis of V/BSA ratio is very useful. It allows us not only to compare the thyroid volume in different time points but also in populations inhabiting different geographic regions. Thus, the differences in thyroid volume in children living in various geographic areas can be objectively determined, even in places classified as areas with sufficient iodine intake. In such cases, the influence of other factors, which might influence thyroid volume, apart from iodine intake, like ethnic factors, goitrogenic factors related to environmental pollution or consumption of specific diet, can be examined and considered.