Objectives: To investigate the relationship between passive smoking at home and the incidence of various cancers in a population-based prospective study.
Methods: The subjects were 9675 Japanese lifelong nonsmoking women aged over 40 years who lived in three municipalities of Miyagi Prefecture, and completed a self-administration questionnaire in 1984. During 9 years of follow-up, 426 cancers were identified by record linkage to the population-based cancer registry. The data were analyzed using the Cox proportional hazards model.
Results: The age-adjusted relative risks (RR) and 95% confidence intervals (CI) of smoking-related cancers and lung cancer for women who had smoking husbands, compared with women whose husbands did not smoke, were 1.7 (0.94 2.9, p = 0.079) and 1.9 (0.81-4.4, p = 0.14), respectively. In contrast, a significant inverse association was observed for breast cancer, the RR (95% CI) was 0.58 (0.34-0.99, p = 0.047). After multivariate adjustment for confounding factors, the risks of smoking-related cancers and breast cancer were materially unchanged.
Conclusions: These results show that passive smoking may affect the risk of cancers other than lung cancer.