Over half of the world's population is exposed to household air pollution from the burning of solid fuels at home. Household air pollution from solid fuel use is a leading risk factor for global disease and remains a major public health problem, especially in low- and mid-income countries. This is a particularly serious problem in China, where many people in rural areas still use coal for household heating and cooking. This review focuses on several decades of research carried out in Xuanwei County, Yunnan Province, where household coal use is a major source of household air pollution and where studies have linked household air pollution exposure to high rates of lung cancer. We conducted a series of case-control and cohort studies in Xuanwei to characterize the lung cancer risk in this population and the factors associated with it. We found lung cancer risk to vary substantially between different coal types, with a higher risk associated with smoky (i.e., bituminous) coal use compared to smokeless (i.e., anthracite) coal use. The installation of a chimney in homes resulted in a substantial reduction in lung cancer incidence and mortality. Overall, our research underscores the need among existing coal users to improve ventilation, use the least toxic fuel, and eventually move toward the use of cleaner fuels, such as gas and electricity.
Coal; household air pollution; lung cancer
To identify common genetic variants that contribute to lung cancer susceptibility, we conducted a multistage genome-wide association study of lung cancer in Asian women who never smoked. We scanned 5,510 never-smoking female lung cancer cases and 4,544 controls drawn from 14 studies from mainland China, South Korea, Japan, Singapore, Taiwan, and Hong Kong. We genotyped the most promising variants (associated at P < 5 × 10-6) in an additional 1,099 cases and 2,913 controls. We identified three new susceptibility loci at 10q25.2 (rs7086803, P = 3.54 × 10-18), 6q22.2 (rs9387478, P = 4.14 × 10-10) and 6p21.32 (rs2395185, P = 9.51 × 10-9). We also confirmed associations reported for loci at 5p15.33 and 3q28 and a recently reported finding at 17q24.3. We observed no evidence of association for lung cancer at 15q25 in never-smoking women in Asia, providing strong evidence that this locus is not associated with lung cancer independent of smoking.
History of chronic lung diseases and household coal use for heating and cooking are established risk factors of lung cancer; however, few studies have been able to explore these risk factors simultaneously. Xuanwei, China, has some of the highest rates of lung cancer in China and most residents experience substantial in-home coal smoke exposures. Using a population-based case-control study of 498 lung cancer cases and 498 age-matched controls, we evaluated the risk of lung cancer in relation to coal smoke exposure and history of chronic lung diseases, including chronic obstructive pulmonary disease (COPD), asthma, tuberculosis (TB), chronic bronchitis, and emphysema. Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated by conditional logistic regression adjusting for potential confounders. We observed an increased risk of lung cancer with history of any chronic lung disease among males (OR=14.2; 95%CI =4.3 to 46.9), females (OR=2.6; 95%CI =1.1 to 6.3), smokers (OR=12.7; 95%CI =3.5 to 45.8), and nonsmokers (OR=2.6; 95%CI =1.1 to 6.4). Specifically, TB (OR=83.7; 95%CI =11.0 to 634.7), COPD (OR=3.2; 95%CI =1.7 to 6.0), and emphysema and chronic bronchitis (OR=3.3; 95%CI =1.7 to 6.4) were associated with increased risks. These findings suggest that history of chronic lung diseases may also increase risk of lung cancer in populations with indoor coal smoke exposures.
Chronic lung disease; lung cancer; never smoking; Xuanwei; China
Xuanwei, China, experiences some of the highest rates of lung cancer in China. While lung cancer risk has been linked to the household use of bituminous coal, no study has comprehensively evaluated the risk of lung cancer associated with the mining of this coal in Xuanwei. In Xuanwei, coal is typically extracted from underground mines, without ventilation, and transported to the surface using carts powered by manpower or electricity.
We evaluated the risk of lung cancer and working as a coal miner, in the absence of diesel exhaust exposure, in a population-based case-control study of 260 male lung cancer cases and 260 age-matched male controls with information on occupational histories. Odds ratios (ORs) and 95% confidence intervals (CIs) for working as a coal miner and years of working as a coal miner were calculated by conditional logistic regression, adjusting for potential confounders, such as smoking and household coal use.
We observed an increased risk of lung cancer among coal miners (OR=2.7; 95%CI =1.3–5.6) compared to non-coal miners. Further, a dose-response relationship was observed for the risk of lung cancer and the number of years working as a coal miner (ptrend=0.02), with those working as miners for more than 10 years experiencing an almost 4-fold increased risk (OR=3.8; 95%CI=1.4–10.3) compared to non-coal miners.
These findings suggest that coal mining in Xuanwei may be a risk factor for lung cancer.
Coal mining; lung cancer; occupation; Xuanwei; China
Common genetic variation may play an important role in altering chronic obstructive pulmonary disease (COPD) risk. In Xuanwei, China, the COPD rate is more than twice the Chinese national average, and COPD is strongly associated with in-home coal use. To identify genetic variation that may be associated with COPD in a population with substantial in-home coal smoke exposures, we evaluated 1,261 single nucleotide polymorphisms (SNPs) in 380 candidate genes potentially relevant for cancer and other human diseases in a population-based case-control study in Xuanwei (53 cases; 107 controls). PTEN was the most significantly associated gene with COPD in a minP analysis using 20,000 permutations (P = 0.00005). SNP-based analyses found that homozygote variant carriers of PTEN rs701848 (ORTT = 0.12, 95%CI = 0.03 - 0.47) had a significant decreased risk of COPD. PTEN, or phosphatase and tensin homolog, is an important regulator of cell cycle progression and cellular survival via the AKT signaling pathway. Our exploratory analysis suggests that genetic variation in PTEN may be an important risk factor of COPD in Xuanwei. However, due to the small sample size, additional studies are needed to evaluate these associations within Xuanwei and other populations with coal smoke exposures.
COPD; cell cycle; apoptosis; AKT; PTEN
Lung cancer rates in Xuanwei County have been among the highest in China for both males and females, and have been causally associated with exposure to indoor smoky (bituminous) coal emissions that contain very high levels of polycyclic aromatic hydrocarbons. There are numerous coal mines across the County. Although lung cancer risk is strongly associated with use of smoky coal as a whole, variation in risk by smoky coal subtype has not been characterized as yet. We conducted a population-based case-control study of 498 lung cancer cases and 498 controls, individually matched to case subjects on age (±2 years) and sex, to examine risk by coal subtype. Odds ratios (ORs) and 95% confidence intervals (CIs) for coal subtype were calculated by conditional logistic regression, adjusting for potential confounders. Overall, smoky coal use was statistically significantly associated with lung cancer risk, as compared to use of smokeless coal or wood (OR=7.7, 95% CI=4.5 to 13.3). Furthermore, there was marked heterogeneity in risk estimates for specific subtypes of smoky coal (test for heterogeneity: p=5.17 × 10−10). Estimates were highest for coal from the Laibin (OR=24.8, 95% CI=12.4 to 49.6) and Longtan (OR=11.6, 95% CI = 5.0 to 27.2) coal types, and lower for coal from other types. These findings strongly suggest that in Xuanwei and elsewhere, the carcinogenic potential of coal combustion products can exhibit substantial local variation by specific coal source.
Coal; lung cancer; indoor air pollution; Xuanwei; China
Telomeres are responsible for the protection of the chromosome ends and shortened telomere length has been associated with risk of multiple cancers. Genetic variation in telomere related genes may alter cancer risk associated with telomere length. Using lung cancer cases (n = 120) and population-based controls (n = 110) from Xuanwei, China, we analyzed telomere length separately and in conjunction with single nucleotide polymorphisms in the telomere maintenance genes POT1, TERT, and TERF2, which we have previously reported were associated with risk of lung cancer in this study. POT1 rs10244817, TERT rs2075786, and TERF2 rs251796 were significantly associated with lung cancer (ptrend ≤ 0.05). The shortest tertile of telomere length was not significantly associated with risk of lung cancer (OR = 1.58; 95% CI = 0.79 – 3.18) when compared to the longest tertile of telomere length. When stratified by genotype, there was a suggestion of a dose-response relationship between tertiles of telomere length and risk of lung cancer among the POT1 rs10244817 common variant carriers (OR (95%CI) = 1.33 (0.47 – 3.75), 3.30 (1.14 – 9.56), respectively) but not among variant genotype carriers (pinteraction = 0.05). Our findings provide evidence that telomere length and genetic variation in telomere maintenance genes may be associated with risk of lung cancer susceptibility and warrant replication in larger studies.
POT1; TERT; TERF2
Smoky coal contains polycyclic aromatic hydrocarbons (PAHs) and has been strongly implicated in etiology of lung cancer in Xuan Wei, China. While PAHs have been demonstrated to form bulky adducts in nuclear DNA, they have a 90-fold greater affinity for mitochondrial DNA (mtDNA). To compensate for mitochondrial dysfunction or damage, mtDNA content is thought to increase. We conducted a population-based case-control study of lung cancer in Xuan Wei, China hypothesizing that mtDNA content is associated with lung cancer risk. Cases (n = 122) and controls (n = 121) were individually matched on age (±2yrs), sex, village of residence, and type of heating/cooking fuel currently used. Lifetime smoky coal use and potential confounders were determined with questionnaires. mtDNA was extracted from sputum and content was determined with quantitative RT-PCR. Odds ratios (OR) and 95% confidence intervals (95% CI) were calculated with unconditional logistic regression. mtDNA content was dichotomized at the median based on the distribution among the controls. mtDNA content > 157 was associated with a 2-fold increase in lung cancer risk (OR = 1.8; 95% CI = 1.0–3.2) compared with those with ≤157 copies. Risk was higher among those >57 years of age compared with those ≤ 57 years (p interaction = 0.01). In summary, mtDNA content was positively associated with lung cancer risk. Furthermore, there was some evidence that mtDNA content was more strongly associated with lung cancer risk among older individuals. However, due to the small sample size, additional studies are needed to evaluate these associations.
The high incidence of lung cancer in Xuanwei County, China has been attributed to exposure to indoor smoky coal emissions that contain polycyclic aromatic hydrocarbons. The inflammatory response induced by coal smoke components may promote lung tumor development. We studied the association between single nucleotide polymorphisms (SNP) in genes involved in innate immunity and lung cancer risk in a population-based case-control study (122 cases and 122 controls) in Xuanwei. A total of 1,360 tag SNPs in 149 gene regions were included in the analysis. FCER2 rs7249320 was the most significant SNP (OR: 0.30; 95% CI: 0.16–0.55; P, 0.0001; false discovery rate value, 0.13) for variant carriers. The gene regions ALOX12B/ALOX15B and KLK2 were associated with increased lung cancer risk globally (false discovery rate value < 0.15). In addition, there were positive interactions between KLK15 rs3745523 and smoky coal use (OR: 9.40; P interaction = 0.07), and between FCER2 rs7249320 and KLK2 rs2739476 (OR: 10.77; P interaction = 0.003). Our results suggest that genetic polymorphisms in innate immunity genes may play a role in the carcinogenesis of lung cancer caused by polycyclic aromatic hydrocarbon-containing coal smoke. Integrin/receptor and complement pathways as well as IgE regulation are particular noteworthy.
lung cancer; innate immunity; single nucleotide polymorphism; polycyclic aromatic hydrocarbon; coal; FERC2; KLK
Tobacco and indoor air pollution from smoky coal are major causes of lung cancer in rural Xuanwei County, China. Tuberculosis has been suggested to increase lung cancer risk, but data from prior studies are limited. We conducted an analysis of data from a retrospective cohort study of 42,422 farmers in Xuanwei. In 1992, interviewers administered a standardized questionnaire that included lifetime medical history, including tuberculosis. Subjects were followed from 1976, with deaths from lung cancer ascertained through 1996. We used proportional hazards regression to assess the association between tuberculosis and subsequent lung cancer mortality. Tuberculosis was reported by 246 subjects (0.6%), and 2459 (5.8%) died from lung cancer during follow-up. Lung cancer mortality was substantially higher in subjects with tuberculosis than in those without (25 vs. 3.1 per 1000 person-years). The association was especially pronounced in the first five years after tuberculosis diagnosis (hazard ratios [HRs] ranging 6.7–13) but remained strong 5–9.9 years (HR 3.4, 95%CI 1.3–9.1) and 10+ years (HR 3.0, 95%CI 1.3–7.3) after tuberculosis. These associations were similar among men and women, and among smoky coal users (70.5% of subjects). Adjustment for demographic characteristics, lung disease, and tobacco use did not affect results. In Xuanwei, China, tuberculosis is an important risk factor for lung cancer. The increased lung cancer risk, persisting years after a tuberculosis diagnosis, could reflect the effects of chronic pulmonary inflammation and scarring arising from tuberculosis.
Common genetic variation may play an important role in altering lung cancer risk. We conducted a pathway-based candidate gene evaluation to identify genetic variations that may be associated with lung cancer in a population-based case–control study in Xuan Wei, China (122 cases and 111 controls). A total of 1260 single-nucleotide polymorphisms (SNPs) in 380 candidate genes for lung cancer were successfully genotyped and assigned to one of 10 pathways based on gene ontology. Logistic regression was used to assess the marginal effect of each SNP on lung cancer susceptibility. The minP test was used to identify statistically significant associations at the gene level. Important pathways were identified using a test of proportions and the rank truncated product methods. The cell cycle pathway was found as the most important pathway (P = 0.044) with four genes significantly associated with lung cancer (PLA2G6 minP = 0.001, CCNA2 minP = 0.006, GSK3β minP = 0.007 and EGF minP = 0.013), after adjusting for multiple comparisons. Interestingly, most cell cycle genes that were associated with lung cancer in this analysis were concentrated in the AKT signaling pathway, which is essential for regulation of cell cycle progression and cellular survival, and may be important in lung cancer etiology in Xuan Wei. These results should be viewed as exploratory until they are replicated in a larger study.
Indoor air pollution has been documented as an important risk factor for chronic obstructive pulmonary disease (COPD), and inflammation is central to the development and progression of COPD. Single nucleotide polymorphisms (SNP) in some cytokine genes have been reported to be associated with COPD. We examined the association between 18 SNPs in 10 cytokine genes and COPD risk in a case-control study conducted in a population with high exposure to indoor smoky coal emissions. The study included 53 COPD cases and 122 healthy community controls. Carriers of the CSF2 117Ile allele had a 2.4-fold higher risk of COPD than the wild type (Thr/Thr) carriers (OR: 2.44; 95% CI: 1.10 – 5.41), and the AA genotype at IL8 -351 was associated with an increased risk of COPD (OR: 2.71; 95% CI: 1.04 – 7.04). When the combined effects of CSF2 117Ile and IL8 -351A were examined, individuals carrying at least one variant in both genes had a five-fold increased risk of COPD (OR: 5.14, 95% CI: 1.32 – 29.86). This study suggests that polymorphisms in both CSF2 and IL8 may play a role in the pathogenesis of COPD, at least in highly exposed populations. However, in view of our relatively small sample size, this study should be replicated in other populations with substantial exposure to indoor air pollutants such as polycyclic aromatic hydrocarbons (PAH) and particulate matter.
COPD; Cytokine; CSF2; IL8; Single nucleotide polymorphism; Indoor air pollution
Residents of the Bayingnormen region of Inner Mongolia have been exposed to arsenic-contaminated well water for over 20 years, but relatively few studies have investigated health effects in this region. We surveyed one village to document exposure to arsenic and assess the prevalence of arsenic-associated skin lesions and self-reported morbidity. Five-percent (632) of the 12,334 residents surveyed had skin lesions characteristics of arsenic exposure. Skin lesions were strongly associated with well water arsenic and there was an elevated prevalence among residents with water arsenic exposures as low as 5 μg/L-10 μg/L. The presence of skin lesions was also associated with self-reported cardiovascular disease.
Arsenic; drinking water; Inner Mongolia; hyperkeratosis; skin lesions
We conducted a retrospective mortality study in an Inner Mongolian village exposed to well water contaminated by arsenic since the 1980s. Deaths occurring between January 1, 1997 and December 1, 2004 were classified according to underlying cause and water samples from household wells were tested for total arsenic. Heart disease mortality was associated with arsenic exposure, and the association strengthened with time exposed to the water source. Cancer mortality and all-cause mortality were associated with well-water arsenic exposure among those exposed 10–20 years. This is the first study to document increased arsenic-associated mortality in the Bayingnormen region of Inner Mongolia.
Arsenic; drinking water; China; Inner Mongolia; mortality; heart disease; cancer
In Xuanwei County, China, unvented indoor coal burning is strongly associated with increased risk of lung cancer and chronic obstructive pulmonary disease. However, the impact of coal burning and stove improvement on risk of pneumonia is not clear.
We conducted a retrospective cohort study among all farmers born 1917 through 1951 and living in Xuanwei as of 1 January 1976. The analysis included a total of 42,422 cohort members. Follow-up identified all deaths in the cohort from 1976 through 1996. Ages at entry into and at exit from follow-up ranged from 24 to 59 years and from 25 to 80 years, respectively. The record search detected 225 deaths from pneumonia, and 32,332 (76%) were alive as of 31 December 1996. We constructed multivariable Cox models (time variable = age) to estimate hazard ratios (HRs) and 95% confidence intervals (CIs).
Use of coal, especially smokeless coal, was positively associated with pneumonia mortality. Annual tonnage and lifetime duration of smoky and smokeless coal use were positively associated with pneumonia mortality. Stove improvement was associated with a 50% reduction in pneumonia deaths (smoky coal users: HR, 0.521; 95% CI, 0.340–0.798; smokeless coal users: HR, 0.449; 95% CI, 0.215–0.937).
Our analysis is the first to suggest that indoor air pollution from unvented coal burning is an important risk factor for pneumonia death in adults and that improving ventilation by installing a chimney is an effective measure to decrease it.
coal; cohort study; indoor air pollution; pneumonia
Objective To test whether improvement in household coal stoves affected the incidence of chronic obstructive pulmonary disease (COPD) in Xuanwei County, China.
Design Retrospective cohort study (follow-up 1976-92) comparing incidence of COPD between groups with and without chimneys.
Participants 20 453 people born into homes with unvented coal stoves;16 606 (81.2%) subsequently changed to stoves with chimneys.
Intervention Installation of a chimney in households in which unvented stoves had been used previously.
Results Installation of a chimney was associated with distinct reduction in the incidence of COPD. Compared with people who did not have chimneys, the Cox-modelled risk ratio (relative risk) was 0.58 (95% confidence interval 0.49 to 0.70, P < 0.001) in men and 0.75 (0.62 to 0.92, P = 0.005) in women. Modelled risk ratios were robust to different Cox model specifications. Relative risks decreased with time since stove improvement. In both sexes, the reduction in risk became unequivocal about 10 years after stove improvement.
Conclusions In Xuanwei, incidence of COPD decreased markedly after household coal stoves were improved.