The Association of Cigarette Smoking with Serum TSH Concentration and Thyroperoxidase Antibody

Background: Although several studies have found an association between tobacco smoking and thyroid disorders such as Graves' disease, Graves' ophtalmopathy, goiter and thyroid multi nodularity, the effect of smoking on thyroid function is controversial. Aim: The aim of this study was to evaluate the association between smoking and serum TSH concentration and the presence of thyroperoxidase antibody (TPO Ab) in Tehranian adults. Subjects and Methods: In this cross sectional community based survey, 1 581 randomly selected subjects with no history of thyroid disorders were studied within the framework of Tehran Lipid and Glucose Study. Serum TSH and TPOAb were measured in a fasting serum sample. Weight and height were measured and BMI was calculated. Smokers were classified into ever and never smokers based on the declaration of participants. Results: Mean Ln TSH values in the ever smoker (0.36 +/- 0.82) was significantly lower than the never smoker (0.6 +/- 0.82) group (p < 0.001) even after adjustment for age and BMI. The odds ratio for hypothyroidism (TSH > 5.8) was 0.4 in the ever smoker group compared to the never one (odds ratio 0.4, 95 % CI = 0.2-0.8). The frequency of positive TPOAb in never smokers was significantly higher than ever smokers (% 13.5 vs. % 6.7, p < 0.001). Conclusion: The results suggest that smoking is associated with decreased serum TSH concentrations, lower risk of hypothyroidism and possibly with a lower frequency of thyroid auto immunity.