Elsevier

Lung Cancer

Volume 84, Issue 1, April 2014, Pages 31-35
Lung Cancer

Smoky coal, tobacco smoking, and lung cancer risk in Xuanwei, China

https://doi.org/10.1016/j.lungcan.2014.01.004Get rights and content

Abstract

Objectives

Lung cancer rates in Xuanwei are the highest in China. In-home use of smoky coal has been associated with lung cancer risk, and the association of smoking and lung cancer risk strengthened after stove improvement. Here, we explored the differential association of tobacco use and lung cancer risk by the intensity, duration, and type of coal used.

Materials and methods

We conducted a population-based case-control study of 260 male lung cancer cases and 260 age-matched male controls. Odds ratios (OR) and 95% confidence interval (CI) for tobacco use was calculated by conditional logistic regression.

Results

Use of smoky coal was significantly associated with an increased risk of lung cancer, and tobacco use was weakly and non-significantly associated with lung cancer risk. When the association was assessed by coal use, the cigarette-lung cancer risk association was null in hazardous coal users and elevated in less hazardous smoky coal users and non-smoky coal users. The risk of lung cancer per cigarette per day decreased as annual use of coal increased (>0–3 tons: OR: 1.09; 95% CI: 1.03–1.17; >3 tons: OR: 0.99; 95% CI: 0.95–1.03). Among more hazardous coal users, attenuation occured at even low levels of usage (>0–3 tons: OR: 1.02; 95% CI: 0.91–1.14; >3 tons: OR: 0.94; 95% CI: 0.97–1.03).

Conclusion

We found evidence that smoky coal attenuated the tobacco and lung cancer risk association in males that lived in Xuanwei, particularly among users of hazardous coal where even low levels of smoky coal attenuated the association. Our results suggest that the adverse effects of tobacco may become more apparent as China's population continues to switch to cleaner fuels for the home, underscoring the urgent need for smoking cessation in China and elsewhere.

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.

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