Expired-air carbon monoxide as a predictor of 16-year risk of all-cause, cardiovascular and cancer mortality

•EACO is an independent determinant for 16-year all-cause and cancer mortality.•Smoking is a better predictor of cardio-vascular mortality than EACO.•The effect of EACO is similar in smokers and non-smokers.•EACO does not seem to be specific of smoking.•EACO could also be a marker of inhaled ambient EACO or endogenous production.

BackgroundMeasurement of expired-air carbon monoxide (EACO) is commonly used to ascertain non-smoking status, although it can also reflect exposures not related to smoking. Our aim was to assess 16-year mortality according to EACO measured at baseline, in a general population.MethodsOur analysis was based on the Third French MONICA population survey (1994-1997). Causes of death were obtained 16 years after inclusion, and assessment of determinants of mortality was based on Cox modeling.ResultsEACO was measured in 2232 apparently healthy participants aged 35-64. During follow-up, 195 deaths occurred (19% were due to cardio-vascular (CV) causes and 49% to cancer). At baseline, the mean EACO was 11.8 (± 7.4) ppm, 4.6 (± 2.5) ppm, 4.3 (± 2.2) ppm for current, former and never smokers, respectively (P < 0.001). After adjustment for main mortality risk factors and smoking, the hazard ratio (HR) for total mortality was 1.03[95% confidence interval: 1.01-1.06] per 1-unit increase in EACO, and it was 1.04[1.01-1.07] for cancer mortality. Adjusted HR for CV mortality was 1.05[1.01-1.10] but did not remain significant after additional adjustment for smoking (0.98[0.91-1.04]). Interactions between EACO and smoking were not significant.ConclusionsIn a general population, baseline EACO is an independent predictor of 16-year all-cause and cancer mortality, after adjustment for confounders including smoking. Given that the effect of EACO is similar among smokers and non-smokers, EACO is probably not solely related to smoking but could also be a marker of inhaled ambient carbon monoxide and/or endogenous production. Besides, smoking better predicts CV mortality than EACO.