Åsvold et al1 have recently reported on lower thyrotropin levels in smokers vs nonsmokers and increasing thyrotropin levels with time following smoking cessation. The data are interesting and may further support the recommendation for patients with Graves disease to stop smoking. However, previous studies have pointed out a direct correlation between thyrotropin level and body mass,2,3 and in addition there is a well-recognized weight-gaining influence of smoking cessation.4,5 Therefore, I wonder if the observed effect of smoking on thyrotropin level could have, at least partially, been attributed to differences in body mass between smokers and nonsmokers and by weight gain following smoking cessation.
Liel Y. Tobacco Smoking and Thyroid Function: Is Weight Gain a Confounder?. Arch Intern Med. 2008;168(1):114. doi:10.1001/archinternmed.2007.15