Solid Fuel, Second-Hand Smoke, and Lung Cancer Mortality: A Prospective Cohort of 323,794 Chinese Never-Smokers.

Rationale Household air pollution and secondhand tobacco smoke are known carcinogens for lung cancer but large-scale estimates of the relationship with lung cancer mortality are lacking. Objectives Using the large-scale cohort China Kadoorie Biobank, we prospectively investigated associations between these two risk factors and lung cancer death among never-smokers. Methods The Biobank recruited 512,715 adults aged 30-79 years from ten regions in China during 2004-2008. Self-reported never-smoking participants were followed up to 31/12/2016 with linkage to mortality data. Total duration of exposure to household air pollution was calculated from self-reported domestic solid fuel use. Exposure to secondhand tobacco smoke was ascertained using exposure at home and/or other places. Hazard ratios and 95% confidence intervals for associations between these two exposures and lung cancer death were estimated using Cox regression, adjusting for key confounders. Measurements and Main Results There were 979 lung cancer deaths among 323,794 never-smoking participants without a previous cancer during 10.2 years of follow-up. There was a log-linear positive association between exposure to household air pollution and lung cancer death, with a 4% increased risk per 5-year increment of exposure (hazard ratio=1.04; 95% confidence interval=1.01-1.06, p-trend=0.0034); and participants with 40.1-50.0 years of exposure had the highest risk compared to the never-exposed (hazard ratio=1.53; 95% confidence interval=1.13-2.07). The association was largely consistent across various subgroups. No significant association was found between secondhand smoke and lung cancer death. Conclusions This cohort study provides new prospective evidence suggesting that domestic solid fuel use is associated with lung cancer death among never-smokers.