Serological evidence of thyroid autoimmunity among schoolchildren in two different socioeconomic environments.

CONTEXT

The mechanisms leading to thyroid autoimmunity are largely unknown.

OBJECTIVE

Our objective was to assess the role of environment in the development of thyroid autoimmunity.

DESIGN

Prevalence of thyroid autoantibodies in two neighboring populations living in completely different socioeconomic circumstances (Russian Karelia and Finland) was studied.

SETTING

We studied two population-based cohorts partly sharing the same ancestry.

PATIENTS OR OTHER PARTICIPANTS

A total of 532 schoolchildren from Russian Karelia and 532 schoolchildren in Finland matched for age, gender, and season of the blood sampling were included.

INTERVENTIONS

There were no interventions.

MAIN OUTCOME MEASURES

The prevalence of thyroid peroxidase antibodies (TPOAb), thyroglobulin antibodies (TGAb) and HLA-DQ alleles was measured.

RESULTS

The prevalence of TPOAb was significantly lower in Russian Karelian than in Finnish children (0.4 vs. 2.6%, P=0.006). A similar difference was observed for TGAb (0.6 vs. 3.4%, P=0.002). Finnish girls tested positive for both TPOAb (4.3 vs. 0.4%, P=0.01) and TGAb (5.3 vs. 0.9%, P=0.01) more frequently than Finnish boys. Seven of the 23 tested subjects with signs of thyroid autoimmunity (30%) had increased serum TSH concentrations as a sign of subclinical hypothyroidism. The frequency of HLA genotypes did not differ between the two countries or between autoantibody-positive and -negative subjects.

CONCLUSIONS

The prevalence of thyroid autoimmunity is lower in Russian Karelia than in Finland. This difference was not related to ethnic background or HLA-DQ alleles. The results support the idea that the Russian Karelian environment, which is characterized by inferior prosperity and standard of hygiene, may provide protection against thyroid autoimmunity.