[Risk of hyperthyroidism in a Tunisian population of smokers].

Objectives: This study aimed to examine the effect of cigarette smoking on thyroid function especially TSH and FT4 levels and to determine the correlation between these parameters and the biological tobacco markers: plasma thiocyanate and cotininuria.

Methods: The initial study was conducted on 300 voluntary subjects, 162 current smokers, 27 former smokers and 111 nonsmokers aged respectively 35.4±16.1, 31.6±1.8 and 38.0±14.6 years. TSH and FT4 levels were determined using electrochemiluminescence, cotinine by homogenous enzymes immunoassay and thiocyanate by selective electrode.

Results: Before and after adjustment for potentials confounder factors, we found a significant decrease of TSH and a significant increase of FT4 levels according to smoking status. In current and former smokers, we found significant decrease in TSH and increase in FT4 levels compared to nonsmokers. Moreover, we noted a significant decrease of TSH levels in subjects smoking more than 40 cigarettes/day compared to those smoking less than 20 cigarettes/day. Additionally, TSH levels were significantly reduced in subjects smoking more than 5 years compared to those who smoked < 5 years. In smokers, cotininuria and plasma thiocyanates presented a negative correlation with TSH and a positive correlation with FT4 levels.

Conclusion: cigarette smoking is associated to perturbations in FT4 and TSH levels, these perturbations were strongly correlated with smoking status parameters. The associations with smoking cessation suggest that smoking may have reversible effects on thyroid function. Therefore, it is recommended to stop or reduce smoking and to introduce testing of thyroid estimation as a routine test, especially in subjects at risk.