Risk of lung cancer associated with domestic use of coal in Xuanwei, China: retrospective cohort study

Abstract

Objective: To estimate the risk of lung cancer associated with the use of different types of coal for household cooking and heating.

Setting: Xuanwei County, Yunnan Province, China.

Design: Retrospective cohort study (follow-up 1976-96) comparing mortality from lung cancer between lifelong users of "smoky coal" (bituminous) and "smokeless coal" (anthracite).

Participants: 27,310 individuals using smoky coal and 9962 individuals using smokeless coal during their entire life.

Main outcome measures: Primary outcomes were absolute and relative risk of death from lung cancer among users of different types of coal. Unadjusted survival analysis was used to estimate the absolute risk of lung cancer, while Cox regression models compared mortality hazards for lung cancer between smoky and smokeless coal users.

Results: Lung cancer mortality was substantially higher among users of smoky coal than users of smokeless coal. The absolute risks of lung cancer death before 70 years of age for men and women using smoky coal were 18% and 20%, respectively, compared with less than 0.5% among smokeless coal users of both sexes. Lung cancer alone accounted for about 40% of all deaths before age 60 among individuals using smoky coal. Compared with smokeless coal, use of smoky coal was associated with an increased risk of lung cancer death (for men, hazard ratio 36 (95% confidence interval 20 to 65); for women, 99 (37 to 266)).

Conclusions: In Xuanwei, the domestic use of smoky coal is associated with a substantial increase in the absolute lifetime risk of developing lung cancer and is likely to represent one of the strongest effects of environmental pollution reported for cancer risk. Use of less carcinogenic types of coal could translate to a substantial reduction of lung cancer risk.

Fig 1 Unadjusted survival analysis in Xuanwei cohort 1976-96: cumulative risk (95% CI) of death from any cause and of death from lung cancer by age, stratified by type of coal used in household stoves and sex

Fig 2 Association between mean time spent indoors at home each day (excluding sleeping) and risk of death from lung cancer among users of smoky coal in household stoves in Xuanwei cohort 1976-96. (Hazard ratios (95% CI) are adjusted for type of stove used, having any formal education, number of rooms in home, number of people in home, family history of lung cancer, prior diagnosis of chronic respiratory diseases, and (men only) having smoked tobacco)

Fig 3 Association between age when participant started cooking and risk of death from lung cancer among women using smoky coal in household stoves in Xuanwei cohort 1976-96. (Hazard ratios (95% CI) are adjusted for time spent indoors at home each day (excluding sleeping), type of stove used, having any formal education, number of rooms in home, number of people in home, family history of lung cancer, and prior diagnosis of chronic respiratory diseases)