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.