Cigarette smoking, cotinine, and blood pressure.

T he primary coronary heart disease (CHD) risk factors are often positively correlated in that many persons who have undesirable levels of one also have undesirable levels of others. Nevertheless, we should not lose sight of risk factors that tend to be inversely related, such as cigarette smoking and blood pressure. A lower mean blood pressure among cigarette smokers than See p 1309 nonsmokers has been demonstrated in several studies based on assessment of smoking habits by questionnaire.1'2 In this issue of Circulation, Benow-itz and Sharp3 have confirmed this negative association among normotensive bus drivers, using serum cotinine levels as an index of cigarette exposure. Cotinine, a metabolite of nicotine and a relatively stable marker of nicotine exposure, is used increasingly in epidemiologic studies as an objective measure of cigarette smoking. At first glance, it is tempting to explain away this negative association by the fact that cigarette smokers tend to be thinner than nonsmokers.4 However, the negative association persisted when body mass index was taken into account. One is also tempted to suggest that because cigarette smoking is often associated with alcohol use in our society, the difference between blood pressures of smokers and nonsmokers would be even more were it not for the blood pressure-raising effects of the alcohol that smokers drink. This bias is also counteracted by control for alcohol consumption in the multivariate analyses performed by Benowitz and Sharp.3 Two possible confounding factors that were not considered are diet and caffeine intake. It is conceivable that dietary differences between smokers and non-smokers (e.g., differences in salt or meat intake) underlie the observed blood pressure differences. Although caffeine can acutely raise blood pressure, The opinions expressed in this editorial comment are not necessarily those of the editors or of the American Heart Association. habitual coffee and tea drinking have been associated with slightly lower blood pressures.5'6 Coffee consumption is associated with cigarette smoking7 and, ideally, should also be taken into account in studies of smoking or cotinine and blood pressure. Because an acute effect of nicotine exposure is raised blood pressure,8 it is fair to ask whether chronic smoking actually causes a decrease in blood pressure. Most of the studies that have shown lower blood pressures in smokers have been cross-sectional, raising the question of time sequence, a crucial issue in judging whether statistical associations are causal. At least one large follow-up study found that the incidence …