Childhood secondhand smoke exposure and respiratory disease mortality among never-smokers: the Japan collaborative cohort study for evaluation of cancer risk.

Background: The main source of secondhand smoke (SHS) exposure during childhood occurs at home due to close family members who smoke. This study examined the association between childhood SHS exposure and the risk of respiratory disease mortality among non-smoking adults.

Methods: Data from 44 233 never-smoking Japanese men and women aged 40-79 years who participated in the JACC study between 1988 and 1990 were analyzed. The Cox proportional hazards model was used to calculate hazard ratios and 95% confidence intervals of respiratory disease mortality according to the number of smoking family members during childhood. Subdistribution HRs (SHRs) were calculated as a competing risk analysis.

Results: A total of 735 deaths from respiratory diseases were documented in a median follow-up of 19.2 years. Living with three or more smoking family members during childhood was associated with a higher risk of respiratory disease mortality in adulthood among women; multivariable SHR compared with participants with no family member smokers during childhood was 1.60 (1.01-2.54) for participants with three or more family members who smoked during their childhood.

Conclusions: SHS exposure from three or more family members during childhood was associated with an increased risk of respiratory disease-related mortality in adulthood.