Thyroid activity in cigarette smokers

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Abstract
Recent studies showed a possible relationship between cigarette smoking and endocrine function. Since changes in thyroid hormone concentrations can have an effect on overall metabolism and influence androgenic and estrogenic steroid activity, the relationship between cigarette smoking and thyroid function was studied. Volunteers were divided into 4 groups according to self-reported and biochemical data, including blood HbCo, plasma cotinine and thiocyanate, and were described as nonsmokers, light moderate and heavy smokers. Substantial decreases were found in serum thyroxine (T4) and triiodothyronine (T3) concentrations in heavy smokers compared with nonsmokers. Reduced serum thyroid hormone levels were not accompanied by a substantial change in serum thyrotropin concentrations. The free T4 index, free T3 index and T4-T3 ratio were not substantially different for either group.