Household Stove Improvements and Reduction of Lung Cancer Risk in Xuanwei, China
In rural Xuanwei County, lung cancer rates are among China's highest. For household heating and cooking, residents traditionally used unvented indoor firepits, which generate very high indoor air pollution concentrations. Unvented "smoky" coal burning is a major lung cancer risk factor in Xuanwei. In recent decades, many residents have changed from firepits to stoves with chimneys (Stove improvement 1), or to portable stoves lighted outdoors and used indoors (improvement 2).
To test whether lung cancer incidence decreases after stove improvement, a cohort of 23,428 Xuanwei residents, born 1917 - 1951, was followed retrospectively from 1976 to 1992. All subjects were lifelong smoky coal users, born into homes with firepits. After birth, 17,187 subjects (73.4%) had improvement 2. Hospital record search detected 1510 lung cancer diagnoses (6.4%) during follow-up. Separate effects of improvements 1 and 2 were assessed with sex-specific incidence curves, Kaplan-Meier curves, and Cox models.
In both men and women, there was clear reduction of lung cancer incidence 10 years and longer after stove improvement. Stove improvement 1 was associated somewhat more strongly than improvement 2 with long-term incidence reduction. With improvement 1, incidence decreased monotonically with time after improvement, and Rrs were lowest >20 years after improvement:0.10 in men (95% confidence interval 0.04.25) 0.23 in women (0.13.41), compared to RR=1 for no stove improvement. With improvement 2, Rrs were lowest more than 10, but less than 20, years after improvement 2: 0.37 in men (0.20-0.70), 0.34 in women (0.15-0.77).
Long tem lung cancer risk decreases after household stove improvement in Xuanwei smoky coal users. This increases confidence that stove improvement can benefit health in developing countries.