The 'healthy smoker': a phenomenon of health selection?

The detrimental effects of smoking on lung function have been recognized for several decades. Evidence comes from cross-sectional studies which emphasize that damage, certainly at the level of the small airways, may be detectable after a relatively short smoking history, and from longitudinal studies which show that smoking is associated with an increased rate of function loss over time. Implicit in most published evaluations of the evidence has been the concept that smoking is a habit taken up at random by the general population, and that those who do and do not take up the habit start out with similar levels of lung function. Published material was reviewed for evidence to the contrary, consistent with a health selection process similar to that shown in relation to workplace exposures and labeled the 'healthy worker' effect. Despite the wealth of published data on the topic of lung function in relation to the smoking habit, much is presented in a way which does not permit the concept of the 'healthy smoker' to be addressed. Nevertheless, this review revealed sufficient evidence from cross-sectional studies, as well as evidence from one longitudinal study to support the concept of the 'healthy smoker' as an individual who takes up the habit because his/her lungs are relatively resistant to the effects of smoking. If correct, this means that previous studies, particularly those which were cross-sectional in design and focussed on younger persons, are likely to have underestimated the consequences of smoking on lung function. The concept of the 'healthy smoker' may also throw light on characteristics which identify the 'susceptible smoker'.