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Secondhand Smoke Exposure and Cardiovascular Effects: Making Sense of the Evidence
establish the effects of indoor-air policies. Although some national databases and surveys include cardiovascular end points, a national database that tracks hospital admission rates and deaths from acute coronary events, similar to the SEER database for cancer, would improve epidemiologic studies.
The committee found a lack of understanding of a mechanism that leads to plaque rupture and from that to an acute coronary event and of how secondhand smoke affects that process. Additional research is necessary to develop reliable biomarkers of early effects on plaque vulnerability to rupture and to improve the design of pathophysiologic studies of secondhand smoke that examine effects of exposure on plaque stability.
All 11 key studies reviewed by the committee have strengths and limitations due to their study design, and none was designed to test the hypothesis that secondhand-smoke exposure causes cardiovascular disease or acute coronary events. Because of those limitations and the consequent variability in results, the committee did not have enough information to estimate the magnitude of the decrease in cardiovascular risk due to smoking bans or to a decrease in secondhand-smoke exposure. A large, well-designed study could permit estimation of the magnitude of the effect. An ideal study would be prospective; would have individual-level data on smoking status; would account for potential confounders, including other risk factors for cardiovascular events (such as obesity and age), would have biomarkers of mainstream and secondhand-smoke exposures (such as blood cotinine concentrations); and would have enough cases to allow separate analyses of smokers and nonsmokers or, ideally, stratification of cases by cotinine concentrations to examine the dose–response relationship. Such a study could be specifically designed for secondhand smoke or potentially could take advantage of existing cohort studies that might have data available or attainable for investigating secondhand-smoke exposure and its cardiovascular effects, such as was done with the INTERHEART study. Existing studies that could be explored to determine their utility and applicability to questions related to secondhand smoke include the Multi-Ethnic Study of Atherosclerosis (MESA) study, the American Cancer Society’s CPS-3, the European Prospective Investigation of Cancer (EPIC), the Framingham Heart Study, and the Jackson Heart Study. Researchers should clearly articulate the assumptions used in their statistical models and include analysis of the sensitivity of results to model choice and assumptions.