Alterations in circulating thyroid hormones in Indian smokers (bidi and cigarette)

T4, T3 and TSH were estimated in 56 bidi and 50 cigarette smokers and their mean estimates were compared with the corresponding values in 25 healthy non-smokers. T4, T3 and their ratios were significantly lower in both bidi and cigarette smokers (p < 0.001). Circulating TSH in both groups of smokers was similar to that in nonsmokers. T4 and T4/T3 were lower in bidi smokers compared to those in cigarette smokers (p < 0.05 and < 0.01, respectively). Severity of smoking affected T4/T3, and TSH in bidi smokers and T4 in cigarette smokers. Normal TSH excluded any significant decrease in thyroid function in smokers. The alterations in circulating T4 and T3 might have been influenced by thyroid hormone production, protein binding as well as peripheral metabolism of T4 by adverse constituents of bidi/cigarette smoke.