• Qiuli Zhang, Liming Li, Margaret Smith, Yu Guo, Gary Whitlock, Zheng Bian, Om Kurmi, Rory Collins, Junshi Chen, Silu Lv, Zhigang Pang, Chunxing Chen, Naying Chen, Youping Xiong, Richard Peto, Zhengming Chen, and China Kadoorie Biobank study collaboration.
• Clinical Trial Service Unit and Epidemiological Studies Unit (CTSU), University of Oxford, Oxford, UK, School of Public Health, Peking University Health Science Center, Beijing, China, Chinese Academy of Medical Sciences, Dong Cheng District, Beijing, China, China National Center For Food Safety Risk Assessment, Chaoyang District, Beijing, China, Licang Center for Disease Control and Prevention, Qingdao, Shandong, China, Heilongjiang Center for Disease Control and Prevention, Harbin, Heilongjiang, China, Meilan Center for Disease Control and Prevention, Haikou, Hainan, China, Guangxi Center for Disease Control and Prevention, Nanning, Guangxi, China and Liuyang Center for Disease Control and Prevention, Changsha, Hunan, China.
• Int J Epidemiol. 2013 Oct 1; 42 (5): 1464-75.

BackgroundExhaled 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.MethodsThe 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.ResultsThe 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).ConclusionIn 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.

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