Predictors of autoimmune thyroid disease.

This case-control study sought to investigate whether thyroid autoimmunity is significantly associated with identifiable and potentially modifiable environmental factors. A total of 324 individuals were recruited: 164 cases (with positive thyroid peroxidase antibodies [TPO-Ab] and/or thyroid-stimulating hormone receptor antibodies [TSH-R Ab]) and 160 controls (negative antibodies) who had been screened for thyroid autoimmunity within the previous 12 months. A questionnaire sought information on drug, social, and reproductive history, stress, and iodine intake, while blood specimens were collected to measure glycosylated hemoglobin, thyroid function, TPO-Ab/TSH-R Ab status, 25-hydroxyvitamin D level, and hepatitis C antibody status. Both TPO-Ab-positive and TSH-R Ab-positive individuals were exposed to a higher amount of smoking pack-years (P = 0.038 and 0.037, respectively). No significant predictors of TSH-R Ab positivity were identified on multivariate regression analysis. The odds for TPO-Ab positivity was increased by female gender (odds ratio [OR] 2.815, 95% confidence interval [CI], 1.387, 5.714; P = 0.004) and discontinuation of smoking (OR 2.367, 95% CI, 1.213, 4.621; P = 0.012), while birth in winter (OR 0.470, 95% CI, 0.253, 0.871; P = 0.017) and higher intake of iodine-rich foods (OR 0.864, 95% CI, 0.761, 0.981; P = 0.024) decreased the odds for TPO-Ab development. Therefore, avoidance of ever starting smoking and correction of iodine deficiency may help protect against TPO-Ab development.