Secondhand smoke and the risk of incident cardiovascular disease among never-smoking women

The prospective association between secondhand smoke (SHS) and the risk of incident cardiovascular disease (CVD) remains unclear. This study was the first to examine the association between SHS and risks of ischemic heart disease (IHD), stroke, and total CVD in a large cohort in Asia. The study followed 24,232 never-smoking women aged 40-59 from around Japan (Akita, Iwate, Nagano, Niigata, Ibaraki, Kochi, Nagasaki, and Okinawa prefectures). Their husbands were classified into never, former, and current smokers. After adjustment for age, body mass index, alcohol consumption, histories of hypertension and diabetes mellitus, medication use for hyperlipidemia, menopausal status, and public health center areas, the hazard ratios (HRs) of CVD according to husbands' smoking status were estimated by Cox proportional hazards models. During the 440,360 person-years follow-up, 846 women had total CVDs (103 IHDs, 744 strokes). The proportional hazard assumption was not assured during the total follow-up from 1990 to 2012, but so was then the follow-up of < and ≥ 10 person-years were examined separately. The multivariable HRs (95% confidence intervals) associated with husbands' current versus non-current smoking was 2.02 (1.19-3.45) for IHD, 1.18 (0.98-1.42) for stroke, and 1.25 (1.05-1.49) for total CVD in the follow-up of ≥10 person-years. The SHS from husbands may raise the risk of IHD among middle-aged never-smoking women.