Association of exposure level to passive smoking with hypertension among lifetime nonsmokers in Japan: a cross-sectional study

Brief exposure to passive smoking immediately elevates blood pressure. However, little is known about the association between exposure to passive smoking and chronic hypertension. We aimed to examine this association in a cross-sectional study, after controlling multiple potential confounders. Participants included 32,098 lifetime nonsmokers (7,216 men and 24,882 women) enrolled in the Japan Multi-Institutional Collaborative Cohort Study. Passive smoking was assessed using a self-administered questionnaire. The single question about exposure to passive smoking had five response options: sometimes or almost never, almost every day, 2 hours/day or less, almost every day, 2 to 4 hours/day, almost every day, 4 to 6 hours/day, and almost every day, 6 hours/day or longer. Hypertension was defined as any of the following: systolic blood pressure >= 140mmHg, diastolic blood pressure >= 90mmHg, or use of antihypertensive medication. Multivariate-adjusted odds ratio (OR) and 95% confidence interval (CI) for hypertension were estimated by exposure level to passive smoking using unconditional logistic regression models. The multivariate-adjusted OR for hypertension in those exposed almost every day was 1.11 (95% CI: 1.03-1.20) compared with those exposed sometimes or almost never. The OR for a 1-hour per day increase in exposure was 1.03 (95% CI: 1.01-1.06, P-for (trend)=.006). This association was stronger in men than in women; the ORs were 1.08 (95% CI: 1.01-1.15, P-for (trend)=.036) and 1.03 (95% CI: 1.00-1.05, P-for (trend)=.055), respectively. Our findings suggest importance of tobacco smoke control for preventing hypertension.