Effect of cigarette smoking on thyroid hormone homeostasis.

Serum thyroxine (T4), triiodothyronine (T3), thyroid stimulating hormone (TSH) and thiocyanate (SCN) levels in 40 smokers smoking filter or non-filter cigarettes were compared to those in 20 control subjects. Both types of cigarette smoking resulted in a decrease in T4 (P < 0.01) and increase in TSH (P < 0.05) to the same degree as compared to control. T3 was found to be higher in the smokers but the rise was not significant. SCN was elevated significantly in the smokers. The filter attached to the cigarette was found to have little or no effect on the alteration of the levels of the biochemical indices studied.