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Secondhand Smoke Exposure and Cardiovascular Effects: Making Sense of the Evidence
results of the key intervention studies reviewed by the committee are for the most part consistent with a decrease in risk as early as a month following reductions in secondhand-smoke exposure; however, given the variability in the studies and the lack of data on the precise timing of interventions, the smoking-ban studies do not provide adequate information on the time it takes to see decreases in acute MIs.
Plausibility of Effect
The committee considered both the biologic plausibility of a causal relationship between a decrease in secondhand-smoke exposure and a decrease in the incidence of acute MI and the plausibility of the magnitude of the effect seen in the key epidemiologic studies after implementation of smoking bans.
The experimental data reviewed in Chapter 3 demonstrate that several components of secondhand smoke, as well as secondhand smoke itself, exert substantial cardiovascular toxicity. The toxic effects include the induction of endothelial dysfunction, an increase in thrombosis, increased inflammation, and possible reductions in plaque stability. The data provide evidence that it is biologically plausible for secondhand smoke to be a potential causative trigger of acute coronary events. The risk of acute coronary events is likely to be increased if a person has preexisting heart disease. The association comports with findings on air-pollution components, such as diesel exhaust (Mills et al., 2007) and PM (Bhatnagar, 2006).
As a “reality check” on the potential effects of changes in secondhand-smoke exposure, the committee estimated the decrease in risk of cardiovascular disease and specifically heart failure that would be expected on the basis of the risk effects of changes in airborne PM concentrations after implementation of smoking bans seen in the PM literature. The PM in cigarette smoke is not identical with that in air pollution, and the committee did not attempt to estimate the risk attributable to secondhand-smoke exposure through the PM risk estimates but rather found this a useful exercise to see whether the decreases seen in the epidemiologic literature are reasonable, given data on other air pollutants that have some common characteristics. The committee’s estimates on the basis of the PM literature support the possibility that changes in secondhand-smoke exposure after implementation of a smoking ban can have a substantial effect on hospital admissions for heart failure and cardiovascular disease.
SUMMARY OF OVERALL WEIGHT OF EVIDENCE
The committee examined three relationships—of secondhand-smoke exposure and cardiovascular disease, of secondhand-smoke exposure and