Abstract
AIMS: We examined whether secondhand smoke exposure in childhood affects the risk of coronary heart disease (CHD) in adulthood. METHODS: In the Japan Collaborative Cohort Study, we analyzed data on 71,459 participants aged 40-79 years, with no history of CHD, stroke, or cancer at baseline (1988-1990) and who completed a lifestyle questionnaire including the number of smoking family members in childhood (0, 1, 2, and 3+ members) and followed them up until the end of 2009. The Cox proportional hazards model was used to calculate the multivariable hazard ratios (HRs) with 95% confidence intervals (CIs) of CHD mortality according to the number of smoking family members in childhood. RESULTS: During the median 18.9 years' follow-up, 955 CHD deaths were reported. There was a dose-response relationship between the number of smoking family members at home and CHD mortality among middle-aged individuals (40-59 years); the multivariable HRs (95% CIs) were 1.08 (0.76-1.54) for 1, 1.35 (0.87-2.08) for 2, and 2.49 (1.24-5.00) for 3+ smoking family members compared with 0 members (p for trend=0.03). The association for 3+ smoking family members among the middle-aged group was more evident in men than in women (the multivariable HRs [95% CIs] were 2.97 [1.34-6.58] and 1.65 [0.36-7.52], respectively) and more evident in non-current smokers than in current smokers (the multivariable HRs [95% CIs] were 4.24 [1.57-11.45] and 1.93 [0.72-5.15], respectively). CONCLUSIONS: Secondhand smoke exposure in childhood was associated with an increased risk of CHD mortality in adulthood, primarily in middle-aged men and non-current smokers.