Abstract
Background Exhaled carbon monoxide (COex) level is positively associated with tobacco smoking and exposure to smoke from biomass/coal burning. Relatively little is known about its determinants in China despite the population having a high prevalence of smoking and use of biomass/coal.Methods The China Kadoorie Biobank includes 512 000 participants aged 30-79 years recruited from 10 diverse regions. We used linear regression and logistic regression methods to assess the associations of COex level with smoking, exposures to indoor household air pollution and prevalent chronic respiratory conditions among never smokers, both overall and by seasons, regions and smoking status.Results The overall COex level (ppm) was much higher in current smokers than in never smokers (men: 11.5 vs 3.7; women: 9.3 vs 3.2). Among current smokers, it was higher among those who smoked more and inhaled more deeply. Among never smokers, mean COex was positively associated with levels of exposures to passive smoking and to biomass/coal burning, especially in rural areas and during winter. The odds ratios (OR) and 95% confidence interval (CI) of air flow obstruction (FEV1/FVC ratio <0.7) for never smokers with COex at 7–14 and ≥14 ppm, compared with those having COex <7, were 1.38 (1.31–1.45) and 1.65 (1.52–1.80), respectively (Ptrend <0.001). Prevalence of other self-reported chronic respiratory conditions was also higher among people with elevated COex (P <0.05).Conclusion In adult Chinese, COex can be used as a biomarker for assessing current smoking and overall exposure to indoor household air pollution in combination with questionnaires.
Highlights
Despite the country’s very high prevalence of smoking among males relatively little is known about the lifestyle and environmental determinants of carbon monoxide level in exhaled breath (COex) levels in China; over half of Chinese men still smoke,[13] and about one-third of the world’s male smokers live in China.[14]
Use of biomarkers such as COex to help validate self-reported smoking status in epidemiological studies will be important for reliable assessment of present and future hazards associated with smoking in China and other developing countries
The main aims of this paper are to determine the relevance to COex level of smoking habits, household air pollution and location of residence, and to assess the associations of COex level with the prevalence of certain respiratory diseases and related symptoms in never smokers
Summary
The carbon monoxide level in exhaled breath (COex) can be measured and cheaply using portable meters that are used both in clinical practice and in research studies.[1,2] Evidence from Europe,[3,4] North America[5,6] and elsewhere[7,8,9] shows that COex levels are on average much higher in smokers than non-smokers, so such measurements have been used as biomarkers for assessing smoking exposure in smoking cessation programmes[10,11] and in clinical, laboratory and epidemiological studies.[7,12] Despite the country’s very high prevalence of smoking among males relatively little is known about the lifestyle and environmental determinants of COex levels in China; over half of Chinese men still smoke,[13] and about one-third of the world’s male smokers live in China.[14]. Many people still live in areas with really high levels of exposure to indoor air pollution which could potentially affect COex level.[15,16]. Exhaled carbon monoxide (COex) level is positively associated with tobacco smoking and exposure to smoke from biomass/coal burning. Little is known about its determinants in China despite the population having a high prevalence of smoking and use of biomass/coal
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