Background: Although many epidemiologic studies have investigated the association between exposure to secondhand smoke (SHS) and risk of coronary heart disease (CHD), few of these studies have assessed exposure measures from different sources over a lifetime. Therefore, we sought to test the association between lifetime cumulative exposure to SHS and risk of myocardial infarction (MI) (as an indication of CHD) among never smokers.
Methods: A population-based case-control study in which participants were 1541 never smokers (284 cases and 1257 controls) drawn from 1197 women and men with incident MI and 2850 healthy controls (aged 35-70 years) identified from 2 Western New York counties between 1995 and 2001. Study subjects were asked to report their exposure to SHS at home, at work, and in public settings from childhood to their present age. Exposure histories from each source were combined to form a cumulative lifetime exposure measure. Multiple logistic regression analysis estimated the association between SHS exposure and case status adjusted for age, sex, education, body mass index, race, drinking status, lifetime physical activity, hypertension, diabetes mellitus, and hypercholesterolemia.
Results: After adjustment for covariates, exposure to SHS was not significantly associated with an increased risk of MI. Compared with participants in the bottom tertile of SHS exposure, those in the top tertile had an odds ratio of 1.19 [95% confidence interval, 0.78-1.82] for MI. Virtually all subjects reported some exposure to SHS over their lifetime, but self-reported exposures declined over time, especially in the period closest to the interview.
Conclusions: Exposure to SHS has declined sharply among nonsmokers in recent years. In the absence of high levels of recent exposure to SHS, cumulative lifetime exposure to SHS may not be as important a risk factor for MI as previously thought.