Smoking is negatively associated with the presence of thyroglobulin autoantibody and to a lesser degree with thyroid peroxidase autoantibody in serum: a population study

Background: Autoimmune thyroid diseases are common and the prevalence of circulating thyroid antibodies (thyroid peroxidase antibody, TPO-Ab and thyroglobulin antibody, Tg-Ab) is high in the population. The knowledge of a possible association between lifestyle factors and circulating thyroid antibodies is limited. Aim: To evaluate the correlation between smoking habits and the presence of circulating TPO-Ab and Tg-Ab. Material and methods: In a cross-sectional comparative population study performed in two areas of Denmark with moderate and mild iodine deficiency, 4649 randomly selected subjects from the population in some predefined age groups between 18 and 65 years were examined. Blood tests were analysed for TPO-Ab and Tg-Ab using assays based on the RIA technique. The participants answered questionnaires, were clinically examined and blood and urine samples collected. Results: Data were analysed in multivariate logistic regression models. There was a negative association between smoking and the presence of thyroid autoantibodies in serum. This association was observed for the presence of TPO-Ab and/or Tg-Ab, TPO-Ab (without respect to Tg-Ab status), Tg-Ab (without respect to TPC-Ab status) and both antibodies together. The association between smoking and thyroid autoantibodies was stronger for Tg-Ab than for TPO-Ab. There was no association between smoking and TPO-Ab measured alone or between smoking and TPO-Ab when Tg-Ab was included in the model as an explanatory variable. Conclusion: Smoking was negatively associated with the presence of thyroid autoantibodies with the strongest association between smoking and Tg-Ab. The study design precludes any conclusions as to the cause of the negative association between smoking thyroid autoantibodies.