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 Table of Contents  
ORIGINAL ARTICLE
Year : 2018  |  Volume : 14  |  Issue : 8  |  Page : 7-13

The relationship of indoor coal use and environmental tobacco smoke exposure with lung cancer in China: A meta-analysis


1 Department of Health Service, Institute of Military Health Management, CPLA, College of Health Service, Second Military Medical University, Shanghai 200433, China
2 Department of Environmental Art Design, Fashion and Art Design Institute, Donghua University, Shanghai 200051, China

Date of Web Publication26-Mar-2018

Correspondence Address:
Lulu Zhang
Institute of Military Health Management, CPLA, College of Health Service, Second Military Medical University, 800 Xiangyin Road, Shanghai 200433
China
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/0973-1482.168965

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 > Abstract 


Objective: To assess the association between long-term exposures to smoky coal, environmental tobacco smoke (ETS) and lung cancer incidence in China.
Methods: A meta-analysis was performed on literature searched through Web of Science, Chinese National Knowledge Infrastructure, Weipu, and Wanfang databases. Odds ratio (OR) with 95% confidence intervals (CIs) was used to assess the strength of association between air pollution and lung cancer in China.
Results: Twenty-eight studies were included in the meta-analysis. Stratification by ETS exposure source, amount, and gender found a variation in effect. The pooled OR (95% CI) for exposure to spousal, parents, and work ETS was 1.153 (1.000–1.329), 2.117 (1.626–2.755), and 1.454 (1.307–1.618), respectively. The OR (95% CI) values related to childhood exposure was 1.297 (1.142–1.473), adulthood exposure 1.102 (0.937–1.296), exposure lower than 20 cigarette/day 1.088 (0.809–1.464), higher than 20 cigarette/day 1.776 (1.392–2.267), male 1.555 (1.304–1.855), female 1.487 (1.265–1.748), and coal use 1.490 (1.330–1.669).
Conclusion: The meta-analysis provided evidence that indoor coal use and ETS were significantly associated with lung cancer in China.

Keywords: Coal use, environmental tobacco smoke exposure, indoor air pollution, lung cancer, meta-analysis


How to cite this article:
Li M, Liu X, Zhang L. The relationship of indoor coal use and environmental tobacco smoke exposure with lung cancer in China: A meta-analysis. J Can Res Ther 2018;14:7-13

How to cite this URL:
Li M, Liu X, Zhang L. The relationship of indoor coal use and environmental tobacco smoke exposure with lung cancer in China: A meta-analysis. J Can Res Ther [serial online] 2018 [cited 2018 Apr 26];14:7-13. Available from: http://www.cancerjournal.net/text.asp?2018/14/8/7/168965




 > Introduction Top


Lung cancer is the leading cause of cancer-related mortality around the world,[1] especially in China for men and women.[2] It was estimated that lung cancer incidence rate was 46.08 per 100,000 people with 605,946 lung cancer cases diagnosed in China in 2010, and the crude mortality rate was 37.00 per 100,000 people with 486,555 patients died from lung cancer.[3] Chen et al.'s research suggested that air pollution accounted for more than 2.5 billion life years of life expectancy of 500 million of Northern China residents.[4]

Besides tobacco smoking, there is growing epidemiological evidence that environmental factors such as indoor and outdoor air pollution were contributing factors of lung cancer.[5],[6],[7] Recent evidence suggested significant associations between outdoor air pollution levels and mortality from lung cancer.[8],[9] Long-term Nitric Oxide Exposure Enhances Lung Cancer Cell Migration.[10] Indoor air pollution was found to play an important role in the development of lung cancer.[11] Household coal use was found to be associated with lung cancer risk among all studies throughout the world, especially those studies from China.[12] Study on association between C1 coal and female lung cancer in Xuanwei, one of the areas that has the highest lung cancer mortality rates in China, lend more support to the link between crystalline silica exposure and lung cancer risk.[13] While some study tested the effect of improvement in household coal stoves on incidence of lung cancer and found that changing from unvented to vented stoves appears to benefit the health of people in China.[14],[15],[16] Among nonsmokers, a considerable proportion of men and women reported exposure to environmental tobacco smoke exposure (ETS) at home or in their workplaces.[17] Exposure to ETS was related to moderately increased risk of all-cause mortality and mortality due to lung cancer.[18]

While the association between exposures to smoky coal, ETS has been studied widely, few studies with sufficient power have examined the association by gender, exposure source, lifetime exposure, and amount of exposure. We aimed to assess the association between long-term exposure to smoky coal, ETS and lung cancer incidence in China.


 > Materials and Methods Top


Search strategy

A systematic literature search was performed through Web of Science, CNKI databases, Weipu databases, and Wanfang databases for all relevant studies on the association between coal use and lung cancer in China. The search strategies were based on combinations of topic words “lung cancer,” “air pollution OR coal OR environmental tobacco exposure,” and “China or Chinese.” Publication language was restricted to English and Chinese, with time span from 1990 to 2014 in our search. The last search update was July 31, 2014. References lists were also screened for additional articles.

Selection criteria

To be included in the meta-analysis, studies had to meet the following criteria: (1) Case–control or cohort studies evaluated the correlation between air pollution and the risk of lung cancer; (2) with explicit population size and a clear study period and location in China; (3) providing sufficient data for estimating the OR and 95% confidence intervals (CIs); and (4) published in language of English or Chinese. The exclusion criteria of the studies were (1) Reviews abstracts comments, letters, and meta-analysis; (2) studies with duplicate or incomplete data; and (3) not for human lung cancer.

Data extraction

Two authors (Li and Liu) extracted the following data from the included studies independently. First author's name, year of publication, country, study period, study site, ethnicity, sample sizes and controls, and source of controls (hospital or population-based controls). In case of disagreements of evaluation, a consensus could be reached through discussion among the authors.

Statistical analysis

OR with 95% CI were used to assess the strength of association between air pollution and lung cancer in China. Subgroup analyses were conducted according to the gender, exposure source, lifetime exposure, and amount of exposure. Data analyses were performed using Stata 11.0 (StataCorp LP, Texas, USA).


 > Results Top


Study selection for meta-analyses

A total of 28 studies were related to lung cancer and air pollution in China and included in meta-analysis, contributing a total of 11362 cases and 13953 controls. [Figure 1] shows the study flow chart of the meta-analysis studies selection. [Table 1] summarizes first author, published year, study period, sample size, sex, sample methods, and study location for each study.
Figure 1: Flow chart of the meta-analysis studies selection

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Table 1: Basic information of the included studies

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Environmental tobacco smoke exposure and lung cancer

[Table 2] shows the estimated pooled OR associated with exposure to ETS exposure. Forest plots were showed in [Figure 1]. Stratification of the studies shows that the pooled OR (95% CI) for lung cancer for exposure to spousal ETS is 1.153 (1.000–1.329), compared with 2.117 (1.626–2.755) for exposure to parents ETS and 1.454 (1.307–1.618) for exposure to work ETS. The values related to childhood exposure and adulthood exposure were OR 1.297 (95% CI 1.142–1.473) and OR 1.102 (95% CI 0.937–1.296). With regard to the amount of ETS, the pooled OR values with 95% CI obtained by the fixed-effect model are 1.088 (0.809–1.464) and 1.776 (1.392–2.267) for exposure lower than 20 cigarette/day and higher than 20 cigarette/day, respectively. The pooled OR (95% CI) for lung cancer for male and female is 1.555 (1.304–1.855) and 1.487 (1.265–1.748).
Table 2: ORs of lung cancer associated with ETS

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No significant heterogeneity was found for those exposure to ETS from spouse (I 2 = 50.4%, P= 0.089). Neither did significant heterogeneity found for male (I 2 = 53.8%, P= 0.070) or study with adulthood exposure to ETS (I 2 = 0.0%, P= 0.997). Significant heterogeneity was observed among studies with ETS exposure in relation to ever exposure (I 2 = 78.7%, P= 0.000), parents (I 2 = 91.5%, P= 0.001), work (I 2 = 86.3%, P= 0.000), childhood (I 2 = 74.2%, P= 0.000), female (I 2 = 84.7%, P= 0.000), and those with daily exposure amount ≥20 cigarettes/day (I 2 = 92.0%, P= 0.000) [Figure 2].
Figure 2: Forest plot of studies reporting lung cancer associated with environmental tobacco smoke exposure

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Coal use and lung cancer

[Table 3] shows the estimated pooled OR associated with exposure to coal use. The pooled OR (95% CI) from studies for lung cancer associated with coal use is 1.490 (1.330–1.669). The pooled OR (95% CI) for male is 1.345 (1.129–1.602), compared with 1.345 (1.129–1.602) for female.
Table 3: ORs of lung cancer associated with coal use

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Significant heterogeneity was observed among studies with coal exposure (I 2 = 95.3%, P= 0.000) [Figure 3].
Figure 3: Forest plot of studies reporting lung cancer associated with coal exposure

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 > Discussion Top


Indoor air pollution appears to have an impact on one's health for the long duration of contact.[48] Coal is one of the major energy resources in China,[49] especially in a rural area. Our meta-analysis found a significant association between coal use and lung cancer in China, which is similar to other studies.[12],[50],[51],[52] Although the following three studies all indicated relationship between coal use and lung cancer, the pooled OR (95% CI) estimate for coal use as lung cancer carcinogen was 1.490 (1.330–1.669), a bit smaller than that reported by Kurmi (OR 1.82, 95% CI 1.60–2.06) and Hosgood (OR 2.15, 95% CI 1.61–2.89).[12],[52] From results studied by Kurmi, the impact of coal use on lung cancer is higher for women (OR 1.81, 95% CI 1.569–2.140) than men (OR 1.345, 95% CI 1.129–1.602). Zhao's research revealed higher risk for both sexes (OR 1.81, 95% CI 1.569–2.140) than women (OR 1.345, 95% CI 1.129–1.602). While, our study suggested a higher risk of lung cancer from coal use for men (OR 1.832, 95% CI 1.569–2.140) than women (OR 1.345, 95% CI 1.129–1.602). That may because many study research the lung cancer in Xuanwei County, where many men exposure to coal mining occupational risk of lung cancer.[20]

With regard to exposure to ETS, many studies documented a significant association between ETS and lung cancer while some studies showed reverse result. For instance, OR (95% CI) for exposure from parents were 0.89 (0.43–1.84), 0.94 (0.74–1.19), and 0.8 (0.4–1.6) in three studies, respectively.[27],[28],[36] OR (95% CI) value for exposure lower than 20 cigarette/day was 0.72 (0.53–0.98) by Lei.[30] The relationship between ETS and lung cancer is comprehensive and there may be many confounders such as recall bias et al. It is likely that owing to misclassification of nonsmoking status, of the disease status or the spouse's smoking habits, some studies failed to support the correlation between ETS and lung cancer.[53],[54],[55] A meta-analysis of study supported the existence of a causal relationship between ETS from spouse and lung cancer with the pooled relative risk (RR) (95% CI) of 1.27 (1.17–1.37),[56] which is similar to our meta-analysis result for Chinese with RR (95% CI) of 1.153 (1.000–1.329). Our study also provided evidence for correlation of ETS in workplace and lung cancer, which was consistent with previous reports.[27],[32],[34],[38],[42] We also found that higher risk of childhood exposure than adulthood exposure, and there may be dose-effect for exposure to ETS more than 20 cigarette/day increase the risk of getting lung cancer. Our results revealed that the pooled OR values for men were higher than that of women. This does not necessary indicated that ETS has more influence on men than women. The synergistic effect of smoking and ETS may give an explanation to this issue. It is possibly the result of more smoking habit among men.

Several studies also conducted a meta-analysis on coal use, ETS and lung cancer.[12],[25],[52],[56],[57],[58] Our study examined the association by gender, exposure source, lifetime exposure, and amount of exposure. Relationship between smoky coal, ETS and lung cancer underscores the importance of policies and public health interventions to reduce exposure to ETS [59] and indicated the need of positive action to reduce household coal exposures through ventilation improvement, stove improvement, and fuel alternation, et al.


 > Conclusion Top


Our meta-analysis provided evidence that indoor coal use and ETS were significantly associated with lung cancer in China.

Acknowledgment

We thank the National Natural Science Foundation of China for financial support.

Financial support and sponsorship

The project was supported by the National Natural Science Foundation of China (71233008, 91224005 and 71303248), Important Disease Joint Research Project in Health Systems of Shanghai (2013ZYJB0006), Military Health Support Strategy and Key Technology Research for special injuries in the South China Sea Region (AWS12J002), the Fundamental Research Funds for the Central Universities, and Young Scientist Fund of Second Military Medical University (2012QN09).

Conflicts of interest

There are no conflicts of interest.



 
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