Biomarker-assessed passive smoking in relation to cause-specific mortality: pooled data from 12 prospective cohort studies comprising 36 584 individuals

Aims While investigators have typically quantified the health risk of passive smoking by utilising self-reported exposure, prospective studies with objective ascertainment, which are less liable to measurement error, are rare. Using data pooling, we examined the relation of a biochemical assessment of passive smoking, salivary cotinine, with mortality from a range of causes. Methods We combined data from twelve cohort studies from England and Scotland initiated between 1998 and 2008. Study members were linked to national death registries. A total of 36 584 men and women aged 16 to 85 years of age reported that they were non-smoking at baseline, provided baseline salivary cotinine, and consented to mortality record linkage. Results A mean of 8.1 years of mortality follow-up of 36 584 non-smokers (16 792 men and 19 792 women) gave rise to 2367 deaths (775 from cardiovascular disease, 780 from all cancers, and 289 from smoking-related cancers). After controlling for a range of covariates, a 10 ng/ml increase in salivary cotinine level was related to an elevated risk of total (hazard ratios; 95% confidence interval: 1.46; 1.16, 1.83), cardiovascular (1.41; 0.96, 2.09), cancer (1.49; 1.00, 2.22) and smoking-related cancer mortality (2.92; 1.77, 4.83). Conclusions Passive smoking assessed biomedically was a risk factor for a range of health outcomes known to be causally linked to active smoking.