LAUSR

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.