A Regional Study on Thyroid Autoimmunity and Iodine Exposure in Bangladeshi Populations

Background: Iodine is required for thyroid function, but both deficiency and excess can affect thyroid health. Bangladesh implemented universal salt iodization to control endemic iodine deficiency, but the effects of varying iodine exposure on thyroid autoimmunity in different regions are unclear. This study aimed to investigate the relationship between iodine status and thyroid autoimmunity in five regions of Bangladesh. Methods: In this cross-sectional study, 100 subjects (20 from each division: Dhaka, Chittagong, Sylhet, Rajshahi, and Rangpur) with no prior history of thyroid disease were enrolled. Urinary iodine levels (UIC) were estimated and graded according to WHO criteria. Thyroid function tests (TSH, free T4, free T3) and thyroid peroxidase antibodies (TPO-Ab) were assessed. Linear regression ascertained the influence of iodine status on fT4 levels, and Cox proportional hazards and logistic regression models ascertained predictors of thyroid autoimmunity. Results: The prevalence of thyroid autoimmunity varied significantly by region, from 50% in Rangpur to 20% in Sylhet. A dose-response relationship between iodine exposure and TPO-Ab positivity was strong since 75% of the subjects with excess iodine levels (≥300 µg/L) were positive for thyroid autoantibodies compared to 19.4% of those who had sufficient iodine levels. Multivariate analysis also demonstrated that high iodine exposure was independently related to a higher risk of thyroid autoimmunity (HR=3.2, 95% CI: 1.8-5.6, p<0.001), independent of age and sex. Conclusion: This study demonstrates a definite association of excessive iodine exposure with thyroid autoimmunity in Bangladesh's population, with a marked geographic variation. The findings suggest that although iodine deficiency prevention is still required, prevention of excessive iodine exposure should be adopted in public health policies to reduce thyroid autoimmunity risk.