Michael J. Thun

Environmental Tobacco Smoke and Coronary Heart Disease in the American Cancer Society CPS-II Cohort

BACKGROUND Thirteen of 14 epidemiological studies have shown an increased risk of approximately 20% for coronary heart disease (CHD) for never-smokers exposed to environmental tobacco smoke (ETS), but this association remains controversial. If true, ETS might account for an estimated 35,000 to 40,000 heart disease deaths per year in the United States. METHODS AND RESULTS We have conducted the largest study to date, a prospective study of 353,180 female and 126,500 male never-smokers enrolled in 1982 in the American Cancer Societys Cancer Prevention Study II and followed through 1989. Analyses focused on subcohorts of 309,599 married pairs and of 135,237 subjects concordant for self-reported exposure and exposure reported by each ones spouse. More than 2800 CHD deaths (ICD 410-414) occurred among married pairs; 10% of married men and 28% of married women were married to currently smoking spouses, while 10% and 32%, respectively, were married to former smokers. After controlling for many cardiovascular risk factors, we found 22% higher CHD mortality (rate ratio, 1.22; 95% CI, 1.07 to 1.40) among never-smoking men married to currently smoking wives compared with those married to wives who had never smoked. The corresponding rate ratio for women was 1.10 (0.96 to 1.27). Never-smokers living with former smokers showed no increased risk. When analyses were restricted to subjects whose ETS exposure was classified via both their own self-report and a spouses report, the rate ratio was 1.23 (1.03 to 1.47) for currently exposed men and 1.19 (0.97 to 1.45) for women. CONCLUSIONS Results are consistent with prior reports that never-smokers currently exposed to ETS have about 20% higher CHD death rates. However, our data do not show consistent dose-response trends and are possibly subject to confounding by unmeasured risk factors.