Smoky coal, tobacco smoking, and lung cancer risk in Xuanwei, China
Introduction
In the rural county of Xuanwei, Yunnan Province, in southwest China, lung cancer mortality rates are up to 15 times higher than in the rest of the country (12.3 per 100,000 in China; up to 186.8 per 100,000 in 1975 for men in the three high-mortality communes of Xuanwei) [1]. Much of the lung cancer risk has been attributed to exposure to indoor smoky coal combustion [1], [2], [3], [4], [5], [6]. The vast majority of residents in Xuanwei have been farmers, and have traditionally cooked indoors in a firepit with smoky coal (bituminous), smokeless coal (anthracite), or wood in poorly ventilated conditions. This mode of combustion generates airborne particulate matter and a variety of toxins and carcinogens such as polycyclic aromatic hydrocarbons (PAHs) [7]. PAH compounds can be readily absorbed into the body and PAH metabolites have been found in the urine of Xuanwei residents [8]. Inhalation of PAHs has been linked to increasing lung cancer risk [9]. In present day Xuanwei, burning coal still occurs in many rural populations [10].
Previous studies in Xuanwei have identified various risk factors associated with the area's unique home cooking and heating practices. The use of smoky coals with high PAH concentrations substantially increased lung cancer risk [11], and access to better cooking conditions reduced lung cancer risk [4], [5]. Worldwide, tobacco smoking is the strongest risk factor for lung cancer where the risk in the heaviest smokers was up to 30-fold higher compared to non-smokers [12]; however, the relative effect of tobacco on lung cancer risk in studies of Xuanwei have been consistently weaker, where the risk in the heaviest smokers was four-fold higher compared to non-smokers [13]. Coal and tobacco contain many known carcinogens [7]. There is significant heterogeneity in the PAH composition in coal [14], [15], even from the same region of the country [11], [16]. Smoking prevalence in the various communes in Xuanwei does not vary significantly [16], suggesting that differences in lung cancer rates geographically could be due to smoky coal use.
Lee et al. reported a stronger association between smoking and lung cancer risk after chimney installation [6]. A study that assessed lung cancer risk with diesel exhaust exposure and tobacco smoking noted a diminished relative effect for each exposure in the presence of high levels of the other [17]. These studies suggest an interaction between carcinogens in fossil fuel and tobacco smoke. Further, potential interactions between the intensity of coal used, and coal type with tobacco use remain underexplored. Here, we assess interactions between the intensity and duration of smoky coal, coal type, and tobacco use on lung cancer risk in a population-based case-control study in Xuanwei males.
Section snippets
Materials and methods
This study population has been described in detail elsewhere [11]. Briefly, this population-based case-control study of lung cancer was conducted in farmers aged 18–85 years, who resided in Xuanwei County for more than one year prior to diagnosis. Cases of lung cancer were diagnosed from November 1985 to February 1990 in one of four hospitals in Xuanwei. These four hospitals account for essentially all lung cancer cases in the region [5]. A total of 500 eligible lung cancer cases were enrolled.
Results
Demographics of the 260 cases and 260 controls are presented in Table 1. Cases tended to smoke more cigarettes than controls, although the difference was not significant (P-value > 0.05). However, controls smoked more pipe tobacco than cases (P-value < 0.05). History of coal mining jobs, familial history of lung cancer, history of non-malignant lung disease, and coal use were significantly different and generally appeared to be greater or more common in cases (all P-values < 0.05).
Odds ratios for
Discussion
We found that the relative effect of smoking on lung cancer risk was stronger in men who used less smoky coal and less hazardous coal. Further, the effect of smoking on the relative risk of lung cancer became most apparent when measured by intensity, and the attenuation appeared even at low levels in Lai Bin/Long Tan coal users.
To the best of our knowledge, this is the first study to evaluate the strength of the association between tobacco smoking and lung cancer risk by the intensity and type
Conflicts of interest
The authors have no conflicts or financial disclosures to make.
Role of the funding source
Funders had no role in the study design, implementation, or analysis of this manuscript.
Acknowledgments
This work was supported by NIH intramural research program and NCI training grant T32-CA105666.
References (24)
- et al.
Tobacco smoking and cancer: a brief review of recent epidemiological evidence
Lung Cancer
(2004) - et al.
Effects of type of smoking (pipe, cigars or cigarettes) on biological indices of tobacco exposure and toxicity
Lung Cancer
(2006) - et al.
The epidemiology of lung-cancer in Xuan Wei, China – current progress, issues, and research strategies
Arch Environ Health
(1988) - et al.
Lung-cancer and indoor air-pollution in Xuan Wei, China
Science
(1987) - et al.
Assessing indoor air-pollution exposure and lung-cancer risk in Xuan Wei, China
J Am Coll Toxicol
(1989) - et al.
Portable stove use is associated with lower lung cancer mortality risk in lifetime smoky coal users
Br J Cancer
(2008) - et al.
Household stove improvement and risk of lung cancer in Xuanwei, China
J Natl Cancer Inst
(2002) - et al.
Differential effects of smoking on lung cancer mortality before and after household stove improvement in Xuan Wei, China
Br J Cancer
(2010) - et al.
Family history of cancer and risk of lung cancer among nonsmoking Chinese women
Cancer Epidemiol Biomarkers Prev
(2007) - et al.
Human exposure and dosimetry of polycyclic aromatic hydrocarbons in urine from Xuan Wei, China with high lung cancer mortality associated with exposure to unvented coal smoke
Carcinogenesis
(1995)