Exhaled Carbon Monoxide as a Potential Biomarker of Household Air Pollution Exposure: A Cross-Sectional Study of 0.5 Million Chinese Adults

Abstract

Background/Aim: Exhaled carbon monoxide (COex) is increasingly used as a biomarker for household air pollution (HAP) exposure, but there is uncertainty about the findings that highlights the need for reliable evidence. We investigated the association between COex and self-reported HAP exposure in 0.5 million adults. Methods: The China Kadoorie Biobank recruited 0.5 million adults aged 30-79 years from 10 diverse localities of China in 2004-2008. At baseline, participants undertook measurement of COex and reported fuel-related HAP exposure. Logistic regression was used to estimate the odds ratio (OR) for HAP exposure indicators with COex level ≥ 7ppm, after adjusting for important confounders. All analyses were conducted separately in never- and current-smokers surveyed in non-winter and winter months. Results: In never-smokers surveyed in non-winter months (n = 231,226; 91% female), higher levels of COex were associated with the use of coal (OR [95% confidence interval]: 2.81 [2.69-2.93]), wood (1.36 [1.28-1.45]) and gas (1.72 [1.57-1.89]) for cooking (compared to electricity), longer duration of cooking (≥ 60 mins: 1.24 [1.20-1.28]), regular use of slow burning stove (1.50 [1.45-1.56]), and exposure to more HAP indicators (≥ three: 2.39 [2.29-2.50]). The associations were stronger in winter. The use of coal (1.59 [1.52-1.66]) and wood (1.32 [1.24-1.41]) for heating were also associated with higher levels of COex compared to those without heating. The results were consistent across rural and urban areas, and they were broadly similar after mutual adjustment of HAP exposure or restriction to female participants not exposed to passive smoking. Current-smokers (n = 111,629, 95% male) who are exposed to ≥ three HAP indicators also had higher levels of COex (non-winter: 1.68 [1.42-1.97]; winter: 1.74 [1.29-2.37]). Conclusions: This large scale study of 0.5 million Chinese adults provides supports for the use of COex as a potential biomarker for HAP particularly for coal-related fuel exposure.