Prevalence and correlates of airflow obstruction in  317 000 never-smokers in China

Abstract

In China, the burden of chronic obstructive disease (COPD) is high in never-smokers but little is known about its causes in this group.We analysed data on 287 000 female and 30 000 male never-smokers aged 30–79 years from 10 regions in China, who participated in the China Kadoorie Biobank baseline survey (2004–2008). Prevalence of airflow obstruction (AFO) (pre-bronchodilator forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) <0.7 and below the lower limit of normal (LLN)) was estimated, by age and region. Cross-sectional associations of AFO (FEV1/FVC <0.7), adjusted for confounding, were examined.AFO prevalence defined as FEV1/FVC <0.7 was 4.0% in females and 5.1% in males (mean ages 51 and 54 years, respectively). AFO prevalence defined as FEV1/FVC <LLN was 5.9% and 5.2%, respectively. In females, odds ratios of AFO were positively associated with lower household income (1.63, 95% CI 1.55–1.72 for lowest versus highest income groups), prior tuberculosis (2.36, 95% CI 2.06–2.71), less education (1.17, 95% CI 1.12–1.23 for no schooling versus college education), rural region and lower body mass index. AFO was positively associated with cooking with coal but not with other sources of household air pollution. Associations were similar for males.AFO is prevalent in Chinese never-smokers, particularly among those with low socioeconomic status or prior tuberculosis, and in rural males.

COPD in nonsmokers: the biomass hypothesis - to be or not to be?

“…Without doubt, the report by SMITH et al [7] is a convincing, valuable addition to the current evidence, even if it challenges the traditional view of burning of biomass as an ''established'' risk factor for chronic respiratory disease, including COPD. These results should be replicated by other (ideally) longitudinal studies and the implications for public health policy to reduce household air pollution should be perhaps revisited in the light of consistent, comparable and convincing evidence.…”

“…SMITH et al [7] found significant, independent associations of CAO with reported history of tuberculosis and also with low household income. Given that pulmonary tuberculosis has a well-defined natural history, distinct from tobacco smoking-related COPD, these associations should be regarded as complications of healed pulmonary tuberculosis and should be considered as a differential diagnosis of COPD in nonsmoking adults, until a better understanding of causal links can be established through cohort studies.…”

“…In this issue of the European Respiratory Journal, SMITH et al [7] report recent findings from the China Kadoorie Biobank, a study of .300 000 nonsmoking Chinese adults living in 10 rural and urban areas. The authors show that the presence of airflow obstruction is common in never-smokers, particularly in rural areas, and it was associated with low socioeconomic status, a history of tuberculosis and low body mass index.…”

Defining airflow obstruction

“…However, it is treated as such, leading to biases in research and clinical medicine. The bias arising from the use of 80% predicted as a cut-off leads to over-estimation of the severity of respiratory impairment and its prevalence rate; it has undoubtedly also affected the otherwise excellent study of SMITH et al [1].…”

Biomarkers in COPD: the search continues!

“…First, most COPD research in the developed world has focused on current and former smokers. Growing literature has examined COPD in never-smokers, particularly in the developing world [6]. The factors that predict COPD development and progression in smokers may differ from those in never-smokers.…”