EDITOR,Although "passive smoking" may be intuitively harmful, the paper by Bonita and colleagues¹ on the risk of stroke and environmental tobacco smoke (ETS) exposure suffers from two fundamental defects. The first is the enormously disproportionate effect due to a small exposure, and the second is the lack of allowance for confounding variables, especially diet.

Serum cotinine concentrations have recently been determined at the US National Center for Environmental Health using the most sensitive method to date of high resolution gas chromatography with mass spectrometry.² In 10 000 subjects it was shown that the mean serum cotinine concentration in ETS exposed non-smokers was 0.6 ng/ml compared to 300 ng/ml in active smokers. This represents 1/500th of the dose received by the active smoker.

It is difficult to reconcile this degree of exposure with an increased risk of stroke which is one quarter that of the active smoker. A similar disproportionate effect . . . [Full text of this article]