Secondhand Smoke Exposure and Cardiovascular Effects Making Sense of the Evidence (2010) / Chapter Skim
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Specifically, the committee reviewed available scientific literature on secondhand-smoke exposure (including short-term exposure) and acute coronary events and characterized the state of the science on the topic with emphasis on the evidence of causality and knowledge gaps that future research should address.
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I secondhand smoke exposure incident could precipitate an acute COMMITTEE'S APPROACH TO ITS CHARGE In response to CDC's request, IOM convened an 11-member committee that included experts in secondhand-smoke exposure, the pharmacology and pathophysiology of secondhand smoke, clinical cardiology, epidemiology (including cardiovascular epidemiology) , and statistics.
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. The committee reviewed the epidemiologic, clinical, and experimental studies relevant to the pathophysiology of secondhand smoke and cardiovascular effects, including coronary heart disease and acute coronary events.
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Those 11 studies are observational studies that examined changes in heart-attack rates after implementation of smoking bans, and they were not designed to answer questions about all three of the associations listed above. Most of them did not measure individual exposures to secondhand smoke or the smoking status of individuals; they were designed to evaluate the association between smoking bans and heart attacks, not the effects of secondhand-smoke exposure.
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The committee therefore did not estimate the size of the effect or the attributable risk. SECONDHAND-SMOkE ExPOSuRE AND ACuTE CORONARy EvENTS Two of the epidemiologic studies reviewed by the committee analyzed changes in the hospitalization rate for acute coronary events after the implementation of smoking bans.
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Thus, those studies provided indirect evidence that at least part of the decrease in acute coronary events seen after implementation of smoking bans could be mediated by a decrease in exposure to secondhand smoke. It is not possible to determine the magnitude of the effect that is attributable to changes in nonsmokers compared with smokers.
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SMOkING BANS AND ACuTE CORONARy EvENTS All 11 key epidemiologic studies are relevant and informative with respect to the questions posed to the committee, and overall they support an association between smoking bans and a decrease in the incidence of acute coronary events. They show remarkable consistency: all the studies showed decreases in the rate of heart attacks (acute MIs)
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The time between implementation of a ban and decreases in secondhand smoke and acute cardiovascular events cannot be determined from the studies, because of the variability among the studies and indeed the difficulty of determining the precise time of onset of a ban. On the basis of its review of the available experimental and epidemiologic literature, including relevant literature on air pollution and PM, the committee concludes that there is a causal relationship between smoking bans and decreases in acute coronary events.
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The evidence includes the results of two key studies that have information on individual smoking status and that showed decreases in risks of acute coronary events in nonsmokers after implementation of a smoking ban. Those studies are supported by information from other smoking-ban studies (although these do not have information on individual smoking status, other exposure-assessment studies have demonstrated that secondhand-smoke exposure decreases after implementation of a smoking ban)
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The key intervention studies that have evaluated the effects of indoor smoking bans consistently have shown a decreased risk of heart attack. Research has also indicated that secondhand-smoke exposure is causally related to heart attacks, that smoking bans decrease secondhand-smoke exposure, and that a relationship between secondhand-smoke exposure and acute coronary events is biologically plausible.
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From page 11... ...
The Saskatoon study had the advantage of comprehensive hospital records, and the Monroe County study excluded smokers. The populationbased studies of the risk of heart attack after the institution of comprehensive smoking bans were consistent in showing an association between the smoking bans and a decrease in the risk of acute coronary events, and this strengthened the committee's confidence in the existence of the association.
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. The baseline rate of acute coronary events or cardiovascular disease could influence the effect size, as would the prevalence of other risk factors for acute coronary events, such as obesity, diabetes, and age.
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• 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 cardiovas cular 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.
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