ArticlesPassive smoking exposure and risk of COPD among adults in China: the Guangzhou Biobank Cohort Study
Introduction
Chronic obstructive pulmonary disease (COPD) is a leading cause of mortality and morbidity worldwide, and is estimated to be the third most common cause of death by 2020.1 Active smoking is well established as the predominant risk factor. However, less than a quarter of all smokers develop COPD and more than 15% of COPD occurs in never smokers, suggesting that other factors also play a part.2
China has one of the largest populations of tobacco consumers worldwide, with smoking rates as high as 70% among men during the 1990s.3 Also, the proportion of never smokers who develop COPD in China is much higher than that in most other countries.4 Compared with women in Europe, the USA, and Canada, Chinese women have a higher risk of respiratory disease, although their smoking rates are lower.5 The proportion of COPD deaths in never smokers is as high as 81% in rural Chinese women.6
Passive smoking has been implicated as a potential risk factor. There is strong evidence of an association between passive smoking exposure in adulthood and respiratory symptoms.7, 8, 9, 10 The evidence on effects of passive smoking exposure and lung function is less consistent.8 A comprehensive review of 23 published studies8 available in Medline up to 2000, and a further eight studies published subsequently,11, 12, 13, 14, 15, 16, 17, 18 show mixed results. Some of these studies included smokers in the analysis14, 15, 19 and only one was from China.20 Furthermore, most previous studies included small samples.
The prevalence of passive smoking exposure is high in China4 and there is not much legislation to restrict exposure in the workplace and public areas. However, there is little information on the effects of passive smoking on lung function in Chinese populations. In this study, we analysed baseline data from 15 379 never smokers among 20 430 participants in the Guangzhou Biobank Cohort Study to examine the relation between passive smoking, self-reported respiratory symptoms, and COPD, based on spirometry.
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Participants
The Guangzhou Biobank Cohort Study is a continuing prospective study among older individuals (50 years and older) that aims to examine environmental and genetic determinants of several chronic diseases in a southern Chinese population. Details of recruitment and description of phase I participants are reported elsewhere.21 Briefly, a community social and welfare association was chosen as a sampling frame. This association, with around 100 000 members, has branches throughout Guangzhou and its
Results
The baseline characteristics of the participants are shown in table 1. The mean age was 61·7 years (range 50–93). There were only 18 people (0·3%) who said they had never smoked who had urinary cotinine levels above 50 ng/mL. Of the 20 430 participants, 15 379 (75·3%) were never smokers. Spirometry data were available for 14 790 (96·1%). Application of the quality algorithm for spirometry measures and visual inspection resulted in rejection of data from 8145 participants. Of the remainder, 148
Discussion
In this study, older adults who were exposed to passive smoking at work and at home, particularly higher level exposure, were associated with higher prevalence of COPD than those not exposed. Passive smoking exposure was also associated with respiratory symptoms. These results were particularly seen when exposure assessment was based on duration of exposure rather than density (as measured by numbers of smokers they were exposed to).
Our study has several strengths. The study population included
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