Environmental tobacco smoke and tobacco related mortality in a prospective study of Californians, 1960-98

Objective To measure the relation between environmental tobacco smoke, as estimated by smoking in Spouses, and long term mortality from tobacco related disease. Design Prospective Cohort Study covering 39 years. Setting Adult population of California, United States. Participants 118 094 adults enrolled in late 1959 in the American Cancer Society cancer prevention study, who were followed until 1998. Particular focus is on the 35 561 never smokers who had a spouse in the study with known smoking habits. Main outcome measures Relative risks and 95% confidence intervals for deaths from coronary heart disease, lung cancer, and chronic obstructive pulmonary disease related to smoking in spouses and active cigarette smoking. Results For participants followed from 1960 until 1998 the age adjusted relative risk (95% confidence interval) for never smokers married to ever smokers compared with never smokers married to never smokers was 0.94 (0.85 to 1.05) for coronary heart disease, 0.75 (0.42 to 135) for lung cancer, and 1.27 (0.78 to 2.08) for chronic obstructive pulmonary disease among 9619 men, mid 1.01 (0.94 to 1.08), 0.99 (0.72 to 1.37), mid 1.13 (0.80 to 1.58), respectively, among 25 942 women. No significant associations were found for current or former exposure to environmental tobacco smoke before or after adjusting for seven confounders and before or after excluding participants with pre-existing disease. No significant associations were found during tire shorter follow tip periods of 1960-5, 1966-72, 1973-85 mid 1973-98. Conclusions The results do not support a causal relation between environmental tobacco smoke and tobacco related mortality, although they do not rule out a small effect. The association between exposure to environmental tobacco smoke and coronary heart disease and lung, cancer may be considerably weaker than generally believed.