Thyroregulatory changes associated with smoking in 70-year-old men.

In a previous study we have analysed serum free T4 concentrations in a representative population of 70-year-old men. In the present study the effect of previous or present tobacco smoking on free T4, T4, T3, rT3, TSH and thyroid hormone binding proteins was analysed in 181 of the 460 men, excluding those with past or present goitre, those who were obviously ill or had died between 70 and 75 years of age and those who had any disease or medication influencing free T4 concentrations. Smokers had higher T4 and rT3 levels, and lower TSH levels but T3 levels no different from non-smokers. The difference in T4 levels, but not rT3 or TSH levels, between smokers and non-smokers could be attributed to differences in body mass and also to differences in TBG levels. The results indicate that tobacco smoking is associated with long-term alterations in thyroregulatory function.