Predictors of autoimmune thyroid disease

Abstract

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.

Keywords:

• Environment
• gender
• iodine
• smoking
• thyroid autoimmunity

ACKNOWLEDGMENTS

The authors thank Mrs. Emily Farrugia, our endocrine nurse, who was of great help in recruiting subjects for the study, as well as all the staff in Mater Dei Hospital’s pathology department, who were involved with the processing and analyses of all the study data.