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.

Figure 1–

Percentages of female never-smokers who a, c) cooked regularly or e, g) used winter heating in their present, previous and before-previous houses, and type of fuel used by those b, d) cooking regularly or f, h) heating their houses, in a, b, e, f) rural and c, d, g, h) urban areas. b, d) For cooking with gas/ electricity, the bar was divided into those cooking with electricity (black) and those cooking with gas (white). f, h) Very few participants used gas for heating any house (0.16% of females heated their current home with gas and considerably fewer used gas for heating previous homes) so the bar was not divided.

Figure 2–

Percentages of male never-smokers who a, c) cooked regularly or e, g) used winter heating in their present, previous and before-previous houses, and type of fuel used by those b, d) cooking regularly or f, h) heating their houses, in a, b, e, f) rural and c, d, g, h) urban areas. b, d) For cooking with gas/ electricity, the bar was divided into those cooking with electricity (black) and those cooking with gas (white). f, h) Very few participants used gas for heating any house (0.26% of males heated their current home with gas and considerably fewer used gas for heating previous homes) so the bar was not divided.

Figure 3–

Prevalence of airflow obstruction (AFO) in a, c) urban and b, d) rural a, b) females and c, d) males plotted against mean baseline age (age groups: 30–39, 40–44, 45–49, 50–54, 55–69, 60–64, 65–69 and 70–79 years). AFO was defined according to modified Global Initiative for Chronic Obstructive Lung Disease (GOLD) grade ≥1 (forced expiratory volume in 1 s/forced vital capacity <0.7) and according to the lower limit of normal (LLN). Vertical lines represent 95% confidence intervals. Prevalences are directly adjusted to the region structure of the male or female baseline population.

Figure 4–

Prevalence of airflow obstruction (AFO) in a) female and b) male never-smokers by region. AFO was defined according to modified Global Initiative for Chronic Obstructive Lung Disease (GOLD) criteria (GOLD grade ≥1: forced expiratory volume in 1 s (FEV₁)/forced vital capacity (FVC) <0.7; GOLD ≥2: FEV₁/FVC <0.7 and FEV₁/predicted FEV₁ for age, sex and height <0.8) and according to the lower limit of normal (LLN). Prevalences are directly adjusted to the 5-year age structure of the female or male never-smoker population at baseline. U: urban; R: rural.