Smoking and the Risk of Gallstones

To the Editor.—  In their case-control study of risk factors for gallstones, Pastides and coworkers¹ found smoking to be protective. It seems that this might well be a spurious association since three previous epidemiologic studies^2-4 of gallstones have reported exactly the opposite finding-smoking appears to increase the risk of gall-stones.In any case-control study, the choice of a suitable control group is critical. The control group selected for this study consisted of patients admitted to a large trauma center; many of the patients had sustained motor vehicle injuries. Smoking is a known risk factor for various types of injury and has been found to increase the risk of motor vehicle accidents and traffic violations by about 50%, even after adjustment for alcohol consumption.⁵ Thus, it appears likely that the apparent protective effect of smoking on gallstones noted by Pastides and coworkers may be largely attributable to excess