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. 2014 Apr 22;11(4):e1001631. doi: 10.1371/journal.pmed.1001631

Burden of Total and Cause-Specific Mortality Related to Tobacco Smoking among Adults Aged ≥45 Years in Asia: A Pooled Analysis of 21 Cohorts

Wei Zheng 1,2,3,*, Dale F McLerran 4, Betsy A Rolland 4, Zhenming Fu 1,2,3,5, Paolo Boffetta 6,7, Jiang He 8, Prakash Chandra Gupta 9, Kunnambath Ramadas 10, Shoichiro Tsugane 11, Fujiko Irie 12, Akiko Tamakoshi 13, Yu-Tang Gao 14, Woon-Puay Koh 15,16, Xiao-Ou Shu 1,2,3, Kotaro Ozasa 17, Yoshikazu Nishino 18, Ichiro Tsuji 19, Hideo Tanaka 20, Chien-Jen Chen 21,22, Jian-Min Yuan 23,24, Yoon-Ok Ahn 25, Keun-Young Yoo 25, Habibul Ahsan 26,27,28,29, Wen-Harn Pan 22,30,31, You-Lin Qiao 32, Dongfeng Gu 33,34, Mangesh Suryakant Pednekar 9, Catherine Sauvaget 35, Norie Sawada 11, Toshimi Sairenchi 36, Gong Yang 1,2,3, Renwei Wang 23,24, Yong-Bing Xiang 14, Waka Ohishi 17, Masako Kakizaki 19, Takashi Watanabe 19, Isao Oze 37, San-Lin You 21, Yumi Sugawara 19, Lesley M Butler 23,24, Dong-Hyun Kim 38, Sue K Park 39, Faruque Parvez 40, Shao-Yuan Chuang 41, Jin-Hu Fan 32, Chen-Yang Shen 42,43, Yu Chen 44, Eric J Grant 17, Jung Eun Lee 45, Rashmi Sinha 46, Keitaro Matsuo 20, Mark Thornquist 4, Manami Inoue 47,48, Ziding Feng 49, Daehee Kang 25, John D Potter 4
Editor: Thomas E Novotny50
PMCID: PMC3995657  PMID: 24756146

Wei Zheng and colleagues quantify the burden of tobacco-smoking-related deaths for adults in Asia.

Please see later in the article for the Editors' Summary

Abstract

Background

Tobacco smoking is a major risk factor for many diseases. We sought to quantify the burden of tobacco-smoking-related deaths in Asia, in parts of which men's smoking prevalence is among the world's highest.

Methods and Findings

We performed pooled analyses of data from 1,049,929 participants in 21 cohorts in Asia to quantify the risks of total and cause-specific mortality associated with tobacco smoking using adjusted hazard ratios and their 95% confidence intervals. We then estimated smoking-related deaths among adults aged ≥45 y in 2004 in Bangladesh, India, mainland China, Japan, Republic of Korea, Singapore, and Taiwan—accounting for ∼71% of Asia's total population. An approximately 1.44-fold (95% CI = 1.37–1.51) and 1.48-fold (1.38–1.58) elevated risk of death from any cause was found in male and female ever-smokers, respectively. In 2004, active tobacco smoking accounted for approximately 15.8% (95% CI = 14.3%–17.2%) and 3.3% (2.6%–4.0%) of deaths, respectively, in men and women aged ≥45 y in the seven countries/regions combined, with a total number of estimated deaths of ∼1,575,500 (95% CI = 1,398,000–1,744,700). Among men, approximately 11.4%, 30.5%, and 19.8% of deaths due to cardiovascular diseases, cancer, and respiratory diseases, respectively, were attributable to tobacco smoking. Corresponding proportions for East Asian women were 3.7%, 4.6%, and 1.7%, respectively. The strongest association with tobacco smoking was found for lung cancer: a 3- to 4-fold elevated risk, accounting for 60.5% and 16.7% of lung cancer deaths, respectively, in Asian men and East Asian women aged ≥45 y.

Conclusions

Tobacco smoking is associated with a substantially elevated risk of mortality, accounting for approximately 2 million deaths in adults aged ≥45 y throughout Asia in 2004. It is likely that smoking-related deaths in Asia will continue to rise over the next few decades if no effective smoking control programs are implemented.

Please see later in the article for the Editors' Summary

Editors' Summary

Background

Every year, more than 5 million smokers die from tobacco-related diseases. Tobacco smoking is a major risk factor for cardiovascular disease (conditions that affect the heart and the circulation), respiratory disease (conditions that affect breathing), lung cancer, and several other types of cancer. All told, tobacco smoking kills up to half its users. The ongoing global “epidemic” of tobacco smoking and tobacco-related diseases initially affected people living in the US and other Western countries, where the prevalence of smoking (the proportion of the population that smokes) in men began to rise in the early 1900s, peaking in the 1960s. A similar epidemic occurred in women about 40 years later. Smoking-related deaths began to increase in the second half of the 20th century, and by the 1990s, tobacco smoking accounted for a third of all deaths and about half of cancer deaths among men in the US and other Western countries. More recently, increased awareness of the risks of smoking and the introduction of various tobacco control measures has led to a steady decline in tobacco use and in smoking-related diseases in many developed countries.

Why Was This Study Done?

Unfortunately, less well-developed tobacco control programs, inadequate public awareness of smoking risks, and tobacco company marketing have recently led to sharp increases in the prevalence of smoking in many low- and middle-income countries, particularly in Asia. More than 50% of men in many Asian countries are now smokers, about twice the prevalence in many Western countries, and more women in some Asian countries are smoking than previously. More than half of the world's billion smokers now live in Asia. However, little is known about the burden of tobacco-related mortality (deaths) in this region. In this study, the researchers quantify the risk of total and cause-specific mortality associated with tobacco use among adults aged 45 years or older by undertaking a pooled statistical analysis of data collected from 21 Asian cohorts (groups) about their smoking history and health.

What Did the Researchers Do and Find?

For their study, the researchers used data from more than 1 million participants enrolled in studies undertaken in Bangladesh, India, mainland China, Japan, the Republic of Korea, Singapore, and Taiwan (which together account for 71% of Asia's total population). Smoking prevalences among male and female participants were 65.1% and 7.1%, respectively. Compared with never-smokers, ever-smokers had a higher risk of death from any cause in pooled analyses of all the cohorts (adjusted hazard ratios [HRs] of 1.44 and 1.48 for men and women, respectively; an adjusted HR indicates how often an event occurs in one group compared to another group after adjustment for other characteristics that affect an individual's risk of the event). Compared with never smoking, ever smoking was associated with a higher risk of death due to cardiovascular disease, cancer (particularly lung cancer), and respiratory disease among Asian men and among East Asian women. Moreover, the researchers estimate that, in the countries included in this study, tobacco smoking accounted for 15.8% of all deaths among men and 3.3% of deaths among women in 2004—a total of about 1.5 million deaths, which scales up to 2 million deaths for the population of the whole of Asia. Notably, in 2004, tobacco smoking accounted for 60.5% of lung-cancer deaths among Asian men and 16.7% of lung-cancer deaths among East Asian women.

What Do These Findings Mean?

These findings provide strong evidence that tobacco smoking is associated with a substantially raised risk of death among adults aged 45 years or older throughout Asia. The association between smoking and mortality risk in Asia reported here is weaker than that previously reported for Western countries, possibly because widespread tobacco smoking started several decades later in most Asian countries than in Europe and North America and the deleterious effects of smoking take some years to become evident. The researchers note that certain limitations of their analysis are likely to affect the accuracy of its findings. For example, because no data were available to estimate the impact of secondhand smoke, the estimate of deaths attributable to smoking is likely to be an underestimate. However, the finding that nearly 45% of the global deaths from active tobacco smoking occur in Asia highlights the urgent need to implement comprehensive tobacco control programs in Asia to reduce the burden of tobacco-related disease.

Additional Information

Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001631.

  • The World Health Organization provides information about the dangers of tobacco (in several languages) and about the WHO Framework Convention on Tobacco Control, an international instrument for tobacco control that came into force in February 2005 and requires parties to implement a set of core tobacco control provisions including legislation to ban tobacco advertising and to increase tobacco taxes; its 2013 report on the global tobacco epidemic is available

  • The US Centers for Disease Control and Prevention provides detailed information about all aspects of smoking and tobacco use

  • The UK National Health Services Choices website provides information about the health risks associated with smoking

  • MedlinePlus has links to further information about the dangers of smoking (in English and Spanish)

  • SmokeFree, a website provided by the UK National Health Service, offers advice on quitting smoking and includes personal stories from people who have stopped smoking

  • Smokefree.gov, from the US National Cancer Institute, offers online tools and resources to help people quit smoking

Introduction

Tobacco smoking is a major risk factor for many diseases, including cardiovascular disease (CVD), respiratory disease, and cancers of the lung and multiple other sites [1],[2]. In the US and many other Western countries, the epidemic of tobacco smoking started in men in the early 1900s and reached its peak in the 1960s; a similar epidemic occurred among women ∼40 y later [3][5]. The main increase in tobacco-related deaths in these countries was not seen until the second half of the 20th century [3],[6][8]. By the 1990s, tobacco smoking accounted for an estimated one-third of all deaths and >50% of cancer deaths in adult men [3],[6][8]. With increasing awareness of smoking-associated risks and heightened anti-smoking campaigns, tobacco use has steadily declined in the US and many other developed countries over the past 20–30 y [3][5],[9],[10], resulting in a recent decrease in lung cancer and other smoking-related diseases in these countries [3],[11].

In Asia, where ∼60% of the world population lives, tobacco control programs are less well developed, particularly in low- and middle-income countries including China and India, the two most populous countries in the world. Inadequate public awareness of smoking risks, combined with aggressive marketing by tobacco companies, has resulted in a sharp increase in tobacco smoking among men in many Asian countries over the past few decades [3],[11],[12]. Smoking prevalence in women was traditionally very low but has increased in recent decades in some Asian countries [3],[11],[12]. More than 50% of men in many Asian countries are smokers [12],[13], approximately twice the level in many Western countries. Despite a recent decline in smoking prevalence in several high-income Asian countries [11],[13], tobacco use in most Asian countries remains very high. Indeed, Asia is now considered the largest tobacco producer and consumer in the world. More than half of the world's 1.1 billion smokers live in Asia [3],[13]. Because many Asian countries are in the early stages of the tobacco epidemic, it is likely that the burden of diseases caused by tobacco smoking will continue to rise over the next few decades, and much longer if the tobacco epidemic remains unchecked.

The size of the effect of tobacco smoking on risk of death, typically measured using smoking-associated relative risks (RRs), varies across countries because of differences in characteristics of smokers, smoking behaviors, and tobacco products. Over the past 15 y, several studies have investigated associations between smoking and selected health outcomes in certain Asian populations and have estimated smoking-associated population attributable risk (PAR) [14][21]. Some studies estimated burden of disease due to smoking in a specific Asian country/region [14],[16],[17],[19],[20]. However, most of these estimates were derived from either a single cohort study or studies using a less-than-optimal research design. In this study, we first estimated RRs of overall and cause-specific mortality associated with tobacco smoking as well as smoking prevalence, using data from ∼1 million participants recruited in 21 prospective cohort studies in seven countries/regions that account for ∼71% of Asia's total population. We then used these estimates and mortality data from the World Health Organization [22] to quantify deaths attributable to tobacco smoking in these Asian populations.

Methods

This study was approved by the ethics committees for all the participating studies and of the Fred Hutchinson Cancer Research Center.

This study utilized resources from a recent pooling project of prospective cohort studies conducted as part of the Asia Cohort Consortium that quantified the association between body mass index and risk of overall and cause-specific mortality in Asians [23]. Cohorts included in the current analysis were in Bangladesh, India, mainland China, Japan, Republic of Korea, Singapore, and Taiwan. A brief description of each of the participating cohort studies is provided in Text S1. All of the cohort studies collected baseline data on demographics, lifestyle factors, body mass index, and history of tobacco smoking, which included current smoking status, duration, and amount and types of tobacco products. Data on all-cause and cause-specific mortality were ascertained through linkage to death certificate data or active follow-up. Additional data were collected on other baseline variables, including education, marital status, alcohol consumption, physical activity, and previous diagnosis of selected diseases, including diabetes, hypertension, cancer, and CVDs. Individual-level data from all participating cohorts were collected and harmonized for statistical analysis.

The association between tobacco smoking and risk of death was examined using Cox proportional hazards regression models, employing a categorical representation of tobacco smoking as the predictor variable. Lifetime nonsmokers were used as the reference for estimating hazard ratios (HRs)—as measures of RR of death for the exposed versus the non-exposed population—and 95% confidence intervals associated with ever, former, and current smoking, as well as pack-years smoked, after adjusting for potential confounders including baseline age, education, urban/rural residence, body mass index, and marital status. All analyses were conducted separately for men and women because of large differences in smoking prevalence. Analyses were country-specific unless otherwise noted. To improve the stability of point estimates in the analyses of pack-years of smoking and for risk of death due to site-specific cancer, as well as types of CVD and respiratory diseases, cohorts were combined into broad ethnic groupings: South Asians (Indians and Bangladeshis) and East Asians (Chinese [including cohorts from mainland China, Singapore, and Taiwan], Japanese, and Koreans), and categorized further among East Asians into Chinese/Koreans and Japanese. No smoking-associated HR was estimated for Bangladesh separately because of the small sample size. The number of Koreans in this study was small, and, thus, they were combined with Chinese individuals in some analyses. Bidi smoking is common in India and Bangladesh; thus, information regarding bidi smoking was incorporated to construct smoking variables, including pack-years smoked (4 bidis = 1 cigarette based on approximately 0.25 and 1.0 g of tobacco per bidi and cigarette, respectively).

In the models, the effect of tobacco smoking on mortality was assumed to be cohort-specific. For each cohort, we assumed that the log-HR for tobacco smoking has a fixed-effect component that is common to all cohorts within each country and a random effect that is cohort-specific. Random effects for log-HRs were assumed to be normally distributed, with mean zero; that is, we assumed that Inline graphic, the estimated log-HR for the j-th smoking level in the i-th cohort, has distribution Inline graphic, where Inline graphic is the within-study variance of Inline graphic as estimated from the Cox regression model and Inline graphic is the between-cohort variance of Inline graphic [24],[25]. Parameter βj and 95% CIs were estimated in the meta-analysis. Age at study entry and exit was used to define the time-to-event variable in the Cox models. Age at study exit was defined as age at date of death or end of follow-up, whichever occurred first. Cox model estimation for each cohort was performed using the PHREG procedure in SAS version 9.2. Meta-analysis estimation was performed using the SAS MIXED procedure.

To estimate PAR, we used the following formula: PAR = P(RR−1)/[P(RR−1)+1], where smoking prevalence and smoking-associated RR are denoted as P and RR (measured using HR in this analysis), respectively. PARs for overall mortality and major causes of death associated with tobacco smoking were estimated for each cohort and then combined using meta-analyses to derive summary PARs per country. To estimate PARs for East Asians (Chinese, Japanese, and Koreans), South Asians (Bangladeshis and Indians), or all seven countries/regions combined, we used the population size of each country/region as a weight to derive weighted HR and smoking prevalence values. To estimate the number of deaths attributable to tobacco smoking, we used World Health Organization age-specific death rates for 2004 for each country. Most of the cohort studies enrolled participants after the mid-1980s; therefore, smoking prevalence rates estimated in this study reflect smoking status in the 1990s (Table 1). Given the long latency of chronic diseases—typically 15 y and longer—it is reasonable to use smoking prevalence rates assessed in the 1990s to estimate number of deaths due to tobacco smoking in 2004.

Table 1. Characteristics of participating cohorts in the Asia Cohort Consortium.

Cohort Number of Participantsa Study Entry Mean Years of Follow-Up Women (Percent) Mean Age at Entry Ever-Smokers (Percent) Number of Deaths Cause of Death (Percent)b
Men Women Cancer CVD Respiratory Diseases Other
India
Mumbai 120,055 1991–1997 5.3 36.4 53.4 31.8 0.5 10,839 8.5 45.0 14.4 32.2
Trivandrum 103,942 1995–2002 7.8 59.6 52.7 60.1 1.8 9,406 10.6 36.6 12.8 40.0
Bangladesh 4,572 2000–2002 6.7 41.0 46.8 83.0 15.5 206 13.7 51.2 10.2 24.9
Mainland China
CHEFS 137,460 1990–1992 7.8 50.9 54.9 63.9 13.4 14,776 23.4 44.8 5.0 26.8
SCS 18,010 1986–1989 16.4 0.0 55.2 57.2 NA 4,902 39.6 33.9 10.7 15.9
SMHS 54,707 2001–2006 3.1 0.0 55.1 69.6 NA 596 53.1 25.7 5.4 15.7
SWHS 67,245 1996–2000 8.7 100.0 51.3 NA 2.7 1,921 48.2 23.5 2.6 25.7
Taiwan
CBCSP 22,961 1991–1992 15.4 50.1 47.2 56.4 1.0 2,400 38.1 19.5 5.9 36.4
CVDFACTS 4,170 1990–1993 15.0 55.8 50.7 54.9 1.3 711 27.5 26.1 10.7 35.7
Singapore (SCHS) 57,714 1993–1999 11.7 56.1 56.1 57.1 8.4 8,234 36.7 33.1 14.8 15.4
Japan
3 Pref Aichi 29,316 1985 12.1 50.6 56.3 84.3 17.5 5,330 32.4 35.0 11.9 20.7
Ibaraki 91,847 1993–1994 11.6 66.3 58.5 77.8 5.6 9,545 NA NA NA NA
JACC 74,465 1988–1990 12.9 56.4 57.0 79.1 6.6 10,099 38.6 29.1 11.4 20.9
JPHC1 40,574 1990–1992 14.7 52.2 49.6 75.7 7.3 3,007 45.0 24.6 6.0 24.3
JPHC2 52,838 1992–1995 11.7 52.9 54.1 75.7 7.6 4,708 44.6 24.1 8.7 22.6
3 Pref Miyagi 18,951 1984 12.0 53.4 56.2 77.1 12.0 3,307 31.0 38.5 11.0 19.5
Miyagi 38,560 1990 12.9 45.2 51.5 81.5 11.1 2,932 54.9 25.9 6.3 12.9
Ohsaki 37,884 1995 10.5 47.0 59.5 81.1 11.0 5,093 37.4 30.7 12.9 19.0
RERF 47,532 1963–1993 22.0 59.2 51.6 86.2 15.5 24,128 27.4 37.2 13.3 22.2
Republic of Korea
KMCC 13,446 1993–2004 6.6 62.5 57.9 79.1 10.0 1,036 29.3 24.8 8.6 37.3
Seoul 13,680 1992–1993 14.7 0.0 49.2 77.3 NA 799 53.6 16.8 3.0 26.7
Total 1,049,929 1963–2006 10.2 51.4 54.3 65.1 7.1 123,975 29.8 35.0 10.8 24.3
a

Including only participants eligible for the current analysis.

b

Deaths from unknown causes are not included.

3 Pref, Three Prefecture Cohort Study; CBCSP, Community-Based Cancer Screening Project; CHEFS, China National Hypertension Survey Epidemiology Follow-Up Study; CVDFACTS, Cardiovascular Disease Risk Factor Two-Township Study; JACC, Japan Collaborative Cohort Study, JPHC, Japan Public Health Center-Based Prospective Study; KMCC, Korea Multi-Center Cancer Cohort; NA, not available; RERF, Radiation Effects Research Foundation; SCHS, Singapore Chinese Health Study; SCS, Shanghai Cohort Study; SMHS, Shanghai Men's Health Study; SWHS, Shanghai Women's Health Study.

The number of deaths from a particular disease attributable to tobacco smoking was calculated by multiplying the PAR for that disease by the total number of deaths in the population from that disease. Analyses also were performed to estimate the number of deaths from a particular disease due to smoking for age groups 45–59, 60–69, and ≥70 y using age-specific HRs and smoking prevalence and then summing these age-specific estimates to obtain the overall number of deaths due to smoking for that disease. This age-specific method yielded similar results to the one without age-specific estimates, and, thus, the latter method was used, as it provides a tighter 95% CI than the age-specific method.

Results

A total of 1,223,092 participants were included in the 21 participating cohorts for this study. Because most studies were conducted among adults aged ≥45 y, participants (n = 70,812) who did not contribute person-years in the age group ≥45 y were excluded from this analysis. Also excluded (not mutually exclusively) were participants with prior history of cancer or CVD at baseline (n = 47,585), with missing data on tobacco smoking (n = 38,898) or vital status (n = 451), or with less than 1 y of observation after baseline survey (n = 30,039). After these exclusions, 1,049,929 participants (510,261 men; 539,668 women) remained (Table 1). Overall, the mean prevalence of tobacco smoking was 65.1% for men and 7.1% for women. Over a mean follow-up of 10.2 y through roughly the mid-2000s for most cohorts, a total of 123,975 deaths were identified in these cohorts.

Compared with never-smokers, a 1.44-fold higher risk (95% CI = 1.37–1.51) of deaths from all causes was observed among male ever-smokers in pooled analyses of all cohorts (Table 2). The estimated HRs related to smoking were slightly higher in Singapore, Republic of Korea, Japan, and Taiwan than in India and mainland China, although 95% CIs overlapped in some of these point estimates (heterogeneity test: p<0.001, I 2 = 89 [95% CI = 85–92]). Among women, ever smoking was associated with a 1.48-fold higher risk (95% CI = 1.38–1.58) of death from any cause. This risk also varied across study populations (heterogeneity test: p<0.001, I 2 = 82 [95% CI = 74–88]). The lowest elevation of risk was observed among Indian women, in which ever smoking was related to a 1.16-fold (95% CI = 0.98–1.36) elevated risk of deaths from all causes. Elevated risk of death was also seen among former smokers, although the risk was lower than among current smokers (Table S1).

Table 2. Association of tobacco smoking with risk of death from all causes in selected study populations in Asia.

Population Men Women
Number of Participants Number of Deaths HR (95% CI)a Number of Participants Number of Deaths HR (95% CI)a
All cohorts combined
Never smoker 177,956 19,353 1.00 501,246 43,067 1.00
Ever smoker 332,305 54,822 1.44 (1.37, 1.51) 38,422 6,733 1.48 (1.38, 1.58)
India
Never smoker 68,866 6,613 1.00 104,223 6,880 1.00
Ever smoker 49,530 6,554 1.31 (1.26, 1.36) 1,378 198 1.16 (0.98, 1.36)
Mainland China
Never smoker 48,664 4,797 1.00 126,085 6,945 1.00
Ever smoker 91,519 9,036 1.30 (1.25, 1.35) 11,154 1,417 1.36 (1.28, 1.45)
Taiwan
Never smoker 5,830 647 1.00 13,696 1,103 1.00
Ever smoker 7,463 1,344 1.44 (1.30, 1.58) 142 17 1.41 (0.85, 2.33)
Singapore
Never smoker 10,875 1,357 1.00 29,645 2,786 1.00
Ever smoker 14,470 3,399 1.58 (1.48, 1.68) 2,724 692 1.75 (1.60, 1.92)
Republic of Korea
Never smoker 4,153 220 1.00 7,567 330 1.00
Ever smoker 14,565 1,180 1.47 (1.26, 1.72) 841 105 1.36 (1.07, 1.73)
Japan
Never smoker 39,108 5,700 1.00 218,448 24,997 1.00
Ever smoker 152,519 33,162 1.49 (1.42, 1.55) 21,892 4,290 1.50 (1.38, 1.63)
East Asians b
Never smoker 108,630 12,721 1.00 395,441 36,161 1.00
Ever smoker 280,536 48,121 1.46 (1.39, 1.54) 36,753 6,521 1.50 (1.40, 1.61)
South Asians c
Never smoker 69,326 6,632 1.00 105,805 6,906 1.00
Ever smoker 51,769 6,701 1.31 (1.26, 1.36) 1,669 212 1.18 (1.01, 1.38)
a

Adjusted for age, education, rural/urban resident, marital status, and body mass index; data from participants with <1 y of follow-up are excluded.

Analyses were conducted among those age 45 y or older.

b

Including data from mainland China, Taiwan, Singapore, Republic of Korea, and Japan.

c

Including data from India and Bangladesh.

Among men, elevated risk of death due to CVD, cancer, and respiratory diseases was statistically significantly associated with ever smoking in virtually all study populations (Table 3). Ever smoking was associated with a 1.35-fold elevated risk (95% CI = 1.26–1.45) of death due to CVD in the analysis that included all cohorts. The risk, however, varied considerably across populations, with the strongest association observed in Taiwan (HR = 1.69; 95% CI = 1.36–2.10) and the weakest association observed in mainland China (HR = 1.17; 95% CI = 1.11–1.25) (heterogeneity test: p<0.001, I 2 = 77 [95% CI = 66–85]). A 1.75-fold elevated risk (95% CI = 1.67–1.85) of death due to cancer in men was associated with ever smoking in the combined analysis of all cohorts. The association with cancer risk was, in general, quite consistent across study populations (heterogeneity test: p = 0.76). For death due to respiratory diseases in men, a 1.53-fold elevated risk (95% CI = 1.39–1.69) was associated with ever smoking in the combined analysis of all cohorts, and no statistically significant heterogeneity was identified (p = 0.29). Among East Asian women, positive associations were also observed between ever smoking and risk of major cause-specific deaths, with HRs ranging from 1.44 (95% CI = 1.23–1.69) for respiratory diseases to 1.59 for CVD (95% CI = 1.41–1.79) and cancer (95% CI = 1.45–1.75). Heterogeneity tests were statistically significant for cancer (p<0.001) and respiratory diseases (p = 0.003) but not for CVD (p = 0.20). Some of the country-specific risk estimates for East Asian women were not statistically significant because of low smoking prevalence among women in Asia. Among Indian women and all South Asian women combined, the association between ever smoking and risk of cause-specific deaths was weak and statistically nonsignificant.

Table 3. Association of tobacco smoking with risk of death from cardiovascular diseases, cancer, or respiratory diseases in selected study populations in Asia.

Population CVD Cancer Respiratory Diseases
Number of Deathsa HR (95% CI)b Number of Deathsa HR (95% CI)b Number of Deathsa HR (95% CI)b
Men
All cohorts combined 15,381/6,526 1.35 (1.26, 1.45) 17,049/3,818 1.75 (1.67, 1.85) 5,671/1,764 1.53 (1.39, 1.69)
India 2,183/2,275 1.27 (1.18, 1.36) 663/379 1.84 (1.59, 2.13) 825/615 1.50 (1.33, 1.69)
Mainland China 3,378/2,055 1.17 (1.11, 1.25) 3,195/1,227 1.72 (1.60, 1.85) 619/326 1.36 (1.18, 1.57)
Taiwan 291/121 1.69 (1.36, 2.10) 488/208 1.63 (1.38, 1.93) 111/43 1.59 (1.09, 2.32)
Singapore 1,050/476 1.43 (1.28, 1.60) 1,313/451 1.85 (1.66, 2.07) 591/190 1.79 (1.51, 2.13)
Republic of Korea 200/43 1.27 (0.90, 1.80) 543/92 1.66 (1.32, 2.10) 72/11 1.67 (0.82, 3.40)
Japan 8,208/1,544 1.35 (1.27, 1.43) 10,825/1,460 1.77 (1.67, 1.88) 3,437/579 1.55 (1.41, 1.70)
East Asiansc 13,127/4,239 1.38 (1.28, 1.49) 16,364/3,438 1.75 (1.66, 1.84) 4,830/1,149 1.54 (1.38, 1.72)
South Asiansd 2,254/2,287 1.26 (1.18, 1.35) 685/380 1.85 (1.59, 2.17) 841/615 1.50 (1.33, 1.69)
Women
All cohorts combined 2,552/13,837 1.54 (1.36, 1.73) 1,752/9,971 1.58 (1.44, 1.74) 655/3,760 1.40 (1.20, 1.63)
India 59/2,316 1.04 (0.77, 1.40) 13/587 1.18 (0.66, 2.10) 29/814 1.05 (0.68, 1.62)
Mainland China 666/2,687 1.48 (1.35, 1.62) 344/1,827 1.56 (1.37, 1.77) 63/323 1.18 (0.89, 1.58)
Taiwan 4/235 1.73 (0.64, 4.71) 12/399 2.94 (1.59, 5.42) 0/63 e
Singapore 230/969 1.50 (1.28, 1.75) 262/992 2.19 (1.90, 2.54) 112/323 2.13 (1.70, 2.67)
Republic of Korea 35/113 1.24 (0.83, 1.88) 18/79 1.46 (0.83, 2.57) 8/22 1.34 (0.54, 3.31)
Japan 1,511/7,502 1.63 (1.37, 1.95) 1,102/6,083 1.49 (1.39, 1.59) 441/2,212 1.40 (1.26, 1.56)
East Asiansc 2,486/11,506 1.59 (1.41, 1.79) 1,738/9,380 1.59 (1.45, 1.75) 624/2,943 1.44 (1.23, 1.69)
South Asiansd 66/2,331 1.07 (0.81, 1.43) 14/591 1.16 (0.66, 2.04) 31/817 1.05 (0.69, 1.61)
a

Number of deaths among ever-smokers/never-smokers are presented.

b

Adjusted for age, education, rural/urban resident, marital status, and body mass index; data from participants with <1 y of follow-up are excluded.

Analyses were conducted among those age 45 y or older.

c

Including data from mainland China, Taiwan, Singapore, Republic of Korea, and Japan.

d

Including data from India and Bangladesh.

e

HR not estimated because of small sample size.

To quantify risk associated with smoking status and pack-years of smoking, we combined cohorts by ethnic background to improve the stability of point estimates. For men (Table 4) and women (Table 5), risk of total mortality and cause-specific mortality was elevated with increased tobacco smoking among current smokers, measured by pack-years of smoking. Excess deaths were also observed among former smokers, compared with never-smokers, although the risk was lower than for current smokers for deaths due to any cause, CVD, and cancer. A substantially elevated risk of death from respiratory diseases was found among former smokers, particularly in Chinese/Koreans and Indians/Bangladeshis. This excess is probably caused by some smokers quitting smoking after they developed respiratory diseases. Risks associated with smoking status and pack-years of smoking were not estimated for South Asian women because of the small sample size.

Table 4. Association of tobacco smoking with risk of death from all causes, cardiovascular diseases, cancer, or respiratory diseases in major Asian male populations.

Population Tobacco Smoking Number of Participants Deaths from All Causesa CVD Deathsa Cancer Deathsa Respiratory Disease Deathsa
Number of Deaths HR (95% CI)b Number of Deaths HR (95% CI)b Number of Deaths HR (95% CI)b Number of Deaths HR (95% CI)b
Chinese and Koreans ( n  = 155,062) Never 69,522 7,021 1 2,695 1 1,978 1 570 1
Ever 85,540 9,904 1.48 (1.43, 1.53) 2,921 1.37 (1.29, 1.47) 3,998 1.77 (1.66, 1.88) 1,188 1.75 (1.57, 1.96)
Former 20,256 2,583 1.27 (1.21, 1.34) 866 1.24 (1.14, 1.35) 839 1.27 (1.16, 1.39) 382 1.87 (1.62, 2.15)
Current c 65,258 7,312 1.61 (1.55, 1.68) 2,053 1.47 (1.37, 1.58) 3,156 2.02 (1.89, 2.16) 806 1.71 (1.51, 1.94)
0–9.9 pack-years 6,928 763 1.34 (1.23, 1.45) 229 1.29 (1.12, 1.49) 285 1.44 (1.26, 1.65) 75 1.41 (1.09, 1.82)
10–19.9 pack-years 11,307 1,078 1.37 (1.28, 1.47) 309 1.30 (1.14, 1.49) 457 1.65 (1.48, 1.85) 82 1.20 (0.94, 1.55)
20–29.9 pack-years 13,632 1,461 1.50 (1.41, 1.60) 401 1.37 (1.22, 1.54) 637 1.88 (1.70, 2.08) 167 1.69 (1.40, 2.04)
≥30 pack-years 33,391 4,010 1.84 (1.75, 1.93) 1,114 1.64 (1.51, 1.79) 1,777 2.42 (2.24, 2.61) 482 2.00 (1.75, 2.30)
Japanese ( n  = 187,002) Never 39,108 5,700 1 1,544 1 1,460 1 579 1
Ever 147,894 32,214 1.48 (1.43, 1.52) 7,958 1.34 (1.26, 1.42) 10,466 1.76 (1.67, 1.87) 3,343 1.54 (1.41, 1.69)
Former 43,248 8,207 1.24 (1.20, 1.28) 1,939 1.14 (1.06, 1.22) 2,423 1.39 (1.30, 1.49) 975 1.46 (1.31, 1.64)
Current c 104,646 24,007 1.60 (1.55, 1.65) 6,019 1.45 (1.37, 1.54) 8,043 1.94 (1.83, 2.05) 2,368 1.57 (1.43, 1.73)
0–9.9 pack-years 4,283 708 1.54 (1.42, 1.68) 183 1.58 (1.34, 1.86) 189 1.50 (1.28, 1.76) 63 1.93 (1.47, 2.54)
10–19.9 pack-years 12,238 2,361 1.65 (1.57, 1.74) 679 1.69 (1.54, 1.86) 701 1.76 (1.60, 1.94) 207 1.55 (1.31, 1.83)
20–29.9 pack-years 25,045 4,796 1.78 (1.71, 1.86) 1,263 1.77 (1.64, 1.92) 1,547 2.02 (1.88, 2.18) 413 1.73 (1.52, 1.98)
≥30 pack-years 63,080 16,142 1.58 (1.53, 1.63) 3,894 1.35 (1.27, 1.44) 5,606 2.00 (1.88, 2.12) 1,685 1.55 (1.41, 1.72)
Indians and Bangladeshis ( n  = 101,278) Never 69,326 6,632 1 2,287 1 380 1 615 1
Ever 31,952 4,500 1.30 (1.23, 1.36) 1,657 1.31 (1.21, 1.43) 520 1.71 (1.44, 2.03) 825 1.46 (1.26, 1.69)
Former 6,860 1,157 1.27 (1.18, 1.37) 399 1.16 (1.03, 1.31) 92 1.78 (1.35, 2.34) 144 1.70 (1.37, 2.10)
Current c 25,092 3,343 1.30 (1.21, 1.39) 1,258 1.41 (1.27, 1.57) 428 1.62 (1.32, 1.99) 681 1.26 (1.05, 1.52)
0–9.9 pack-years 6,654 597 1.17 (1.06, 1.30) 247 1.32 (1.12, 1.55) 62 1.17 (0.85, 1.62) 71 1.10 (0.81, 1.49)
10–19.9 pack-years 6,623 704 1.22 (1.11, 1.35) 270 1.35 (1.15, 1.58) 95 1.69 (1.28, 2.24) 101 1.17 (0.89, 1.55)
20–29.9 pack-years 4,466 610 1.35 (1.22, 1.49) 222 1.39 (1.17, 1.65) 89 1.82 (1.36, 2.46) 88 1.37 (1.05, 1.80)
≥30 pack-years 7,349 1,432 1.39 (1.28, 1.50) 519 1.51 (1.32, 1.72) 182 1.76 (1.38, 2.25) 222 1.32 (1.06, 1.64)
a

Excluding participants with less than 1 y of follow-up.

b

Adjusted for age, education, rural/urban resident, marital status, and body mass index.

Analyses were conducted among those age 45 y or older.

c

Excluding current smokers with missing information on pack-years of smoking.

Table 5. Association of tobacco smoking with risk of death from all causes, cardiovascular diseases, cancer, or respiratory diseases in major East Asian female populations.

Population Tobacco Smoking Number of Participants Deaths from All Causesa CVD Deathsa Cancer Deathsa Respiratory Disease Deathsa
Number of Deaths HR (95% CI)b Number of Deaths HR (95% CI)b Number of Deaths HR (95% CI)b Number of Deaths HR (95% CI)b
Chinese and Koreans ( n  = 182,640) Never 176,993 11,164 1 4,004 1 3,297 1 731 1
Ever 5,647 1,028 1.65 (1.53, 1.77) 362 1.57 (1.39, 1.77) 356 1.98 (1.75, 2.24) 128 1.98 (1.61, 2.45)
Former 1,609 305 1.38 (1.22, 1.56) 121 1.35 (1.11, 1.65) 86 1.62 (1.29, 2.04) 28 1.62 (1.08, 2.41)
Current c 4,020 722 1.79 (1.65, 1.95) 241 1.73 (1.50, 2.00) 269 2.15 (1.88, 2.47) 100 2.37 (1.88, 3.00)
0–9.9 pack-years 1,930 244 1.59 (1.39, 1.82) 79 1.56 (1.24, 1.98) 93 1.86 (1.50, 2.30) 31 2.16 (1.48, 3.16)
10–19.9 pack-years 757 132 1.77 (1.48, 2.13) 38 1.52 (1.08, 2.14) 55 2.52 (1.90, 3.33) 14 1.91 (1.09, 3.37)
≥20 pack-years 1,333 346 2.01 (1.79, 2.26) 124 2.01 (1.65, 2.43) 121 2.39 (1.96, 2.91) 55 2.87 (2.13, 3.86)
Japanese ( n  = 239,171) Never 218,448 24,997 1 7,502 1 6,083 1 2,212 1
Ever 20,723 4,053 1.42 (1.38, 1.48) 1,461 1.46 (1.37, 1.54) 1,043 1.49 (1.39, 1.60) 416 1.39 (1.25, 1.55)
Former 3,957 788 1.24 (1.15, 1.34) 302 1.23 (1.09, 1.39) 203 1.43 (1.24, 1.65) 75 1.13 (0.89, 1.44)
Current c 16,766 3,265 1.48 (1.42, 1.53) 1,159 1.53 (1.43, 1.63) 840 1.51 (1.40, 1.63) 341 1.48 (1.31, 1.66)
0–9.9 pack-years 6,001 990 1.43 (1.34, 1.52) 339 1.48 (1.32, 1.65) 230 1.35 (1.18, 1.54) 99 1.46 (1.19, 1.79)
10–19.9 pack-years 4,831 828 1.48 (1.38, 1.59) 296 1.57 (1.39, 1.78) 210 1.46 (1.27, 1.68) 96 1.76 (1.43, 2.18)
≥20 pack-years 5,934 1,447 1.52 (1.43, 1.60) 524 1.56 (1.43, 1.71) 400 1.70 (1.53, 1.88) 146 1.45 (1.21, 1.72)
a

Excluding participants with less than 1 y of follow-up.

b

Adjusted for age, education, rural/urban resident, marital status, and body mass index.

Analyses were conducted among those age 45 y or older.

c

Excluding current smokers with missing information on pack-years of smoking.

Further analyses were performed to estimate smoking-associated HRs for selected cancers as well as for other common diseases (Table 6). Among men and women, the strongest association with tobacco smoking was lung-cancer mortality: a 3- to 4-fold elevated risk consistently across all populations. In East Asian men, ever smoking was also associated with elevated risk for cancers of the mouth/pharynx/larynx, esophagus, stomach, colorectum, liver, pancreas, and bladder, cancers that have been consistently related to smoking in previous studies. HR estimates for South Asians were statistically nonsignificant or unreliable for several cancers, probably because of small sample sizes. Because of the relatively small sample size of female ever-smokers in South Asia, results are presented for East Asian women only. As in men, risks were elevated for virtually all smoking-related cancers.

Table 6. Association of tobacco smoking with risk of cause-specific death by study populations in Asia.

Cause of Death Men Women
Chinese/Koreans Japanese South Asians Chinese/Koreans Japanese
Number of Deathsa HRb (95% CI) Number of Deathsa HRb (95% CI) Number of Deathsa HRb (95% CI) Number of Deathsa HRb (95% CI) Number of Deathsa HRb (95% CI)
Cancer
Mouth/pharynx/larynx 290/106 1.95 (1.51, 2.50) 286/36 1.89 (1.28, 2.79) 165/60 1.36 (0.94, 1.98) 16/97 1.99 (1.11, 3.59) 16/81 2.29 (1.28, 4.11)
Esophagus 360/123 1.54 (0.66, 3.57) 625/44 3.05 (2.21, 4.22) 52/9 3.13 (1.43, 6.86) 25/139 0.92 (0.54, 1.57) 21/82 2.62 (1.54, 4.46)
Stomach 855/352 1.43 (1.24, 1.64) 2,440/381 1.48 (1.32, 1.66) 43/16 1.40 (0.67, 2.94) 68/502 1.14 (1.08, 1.52) 191/1,150 1.32 (1.09, 1.59)
Colorectal 490/301 1.13 (0.93, 1.37) 1,123/222 1.22 (1.01, 1.47) 17/11 0.98 (0.40, 2.36) 76/541 1.40 (1.08, 1.83) 124/939 1.11 (0.89, 1.39)
Liver 1,019/460 1.35 (1.19, 1.53) 1,448/198 1.74 (1.48, 2.04) 40/20 1.00 (0.46, 2.16) 67/428 1.75 (1.05, 2.84) 135/621 1.83 (1.50, 2.24)
Pancreas 222/107 1.18 (0.75, 1.86) 658/100 1.60 (1.27, 2.01) 7/6 c 31/200 1.65 (1.08, 2.53) 98/578 1.59 (1.21, 2.09)
Lung 2,124/374 3.56 (2.45, 5.16) 2,866/164 4.12 (3.49, 4.87) 108/20 3.16 (1.76, 5.69) 291/729 3.34 (2.29, 4.86) 253/714 3.15 (2.70, 3.68)
Bladder 80/30 1.97 (1.26, 3.09) 199/26 1.84 (1.07, 3.16) 12/2 c 8/36 1.41 (0.56, 3.52) 17/86 1.63 (0.92, 2.90)
Breast 60/507 1.45 (1.05, 1.99) 74/467 1.40 (1.07, 1.84)
Cervix uteri 19/150 1.04 (0.58, 1.88) 28/122 2.09 (1.32, 3.30)
Other 855/432 1.22 (1.07, 1.40) 2,375/457 1.26 (1.12, 1.42) 131/76 1.11 (0.76, 1.62) 118/898 1.41 (1.13, 1.76) 283/1,945 1.17 (1.01, 1.36)
CVD
CHD 1,828/903 1.52 (1.22, 1.90) 2,264/327 1.72 (1.52, 1.95) 1,159/553 1.57 (1.38, 1.78) 343/1,347 1.68 (1.47, 1.92) 391/1,579 1.89 (1.60, 2.23)
Stroke 2,733/1,613 1.19 (1.11, 1.28) 4,193/896 1.19 (1.10, 1.29) 411/261 1.09 (0.90, 1.32) 453/2,390 1.37 (1.16, 1.63) 787/4,075 1.62 (1.27, 2.07)
Other 1,491/877 1.36 (1.09, 1.70) 3,186/589 1.42 (1.26, 1.60) 115/35 1.01 (0.62, 1.64) 379/1,477 1.46 (1.29, 1.67) 636/3,201 1.42 (1.23, 1.64)
Respiratory disease
COPD 820/224 2.05 (1.40, 3.01) 728/75 2.73 (1.93, 3.31) 522/208 1.28 (1.05, 1.57) 95/223 2.82 (1.18, 6.72) 95/262 2.10 (1.18, 3.72)
Other 755/457 1.09 (0.93, 1.29) 3,158/606 1.42 (1.29, 1.55) 77/45 1.07 (0.68, 1.68) 131/643 1.46 (1.13, 1.88) 405/2,246 1.38 (1.19, 1.60)
Tuberculosis 151/75 0.88 (0.64, 1.23) 56/14 0.66 (0.27, 1.60) 225/65 1.81 (1.21, 2.70) 12/76 0.90 (0.43, 1.85) 9/21 2.43 (0.92, 6.46)
All other known causes 3,369/1,956 1.11 (1.02, 1.20) 5,935/1,206 1.23 (1.13, 1.34) 1,342/818 1.09 (0.97, 1.21) 542/3,619 1.14 (1.00, 1.29) 943/5,307 1.35 (1.12, 1.62)
a

Number of deaths among ever-smokers/never-smokers are presented.

b

HRs estimated for ever-smokers compared with never-smokers and adjusted for age, education, rural/urban residence, marital status, and body mass index; data from participants with <1 y of follow-up are excluded.

Analyses were conducted among those age 45 y or older.

c

HR not estimated because of small sample size.

CHD, coronary heart disease; COPD, chronic obstructive pulmonary disease.

Among East Asian men and women, risks of death associated with smoking were elevated for coronary heart disease, stroke, and chronic obstructive pulmonary disease. Among South Asian men, the association was statistically significant for coronary heart disease and chronic obstructive pulmonary disease but not for stroke. Smoking was associated with elevated risk of death due to tuberculosis in South Asians. However, no association between smoking and tuberculosis was found in East Asians.

Among men ≥45 y, approximately 15.8% (95% CI = 14.3%–17.2%) of deaths (1.34 million [95% CI = 1.21–1.46 million]) from all causes in 2004 were attributable to tobacco smoking in these seven countries/regions combined (Table 7). Smoking-associated PARs for all-cause mortality were higher in Japan (27.7%), Republic of Korea (26.9%), and Singapore (24.8%) than in mainland China (16.2%), India (11.5%), Taiwan (19.7%), and Bangladesh (14.3%). Among women ≥45 y, tobacco smoking accounted for ∼3.3% (95% CI = 2.6%–4.0%) of total deaths (239,000 [95% CI = 188,300–289,700]) in the seven countries/regions combined in 2004.

Table 7. Smoking prevalence, population attributable risk, and number of deaths due to tobacco smoking in selected Asian populations.

Population Men Women
Smoking Prevalence (Percent) PAR (Percent) Number of Deaths (in Thousands) Smoking Prevalence (Percent) PAR (Percent) Number of Deaths (in Thousands)
Bangladesh 53.8a 14.3 (12.2, 16.4)b 46.4 (39.6, 53.3) 3.0a 0.5 (0.0, 1.1)b 1.5 (0, 3.4)
India 41.8 11.5 (9.8, 13.2) 378.8 (322.8, 434.8) 1.3 0.2 (0.0, 0.4) 6.9 (0, 11.0)
Mainland China 65.3 16.2 (14.0, 18.5) 675.7 (583.9, 771.6) 8.1 2.9 (2.2, 3.5 104.6 (79.4, 126.3)
Taiwanc 56.1 19.7 (14.6, 24.7) 18.4 (13.6, 23.0) 4.2a 1.7 (0.0, 4.6) 1.0 (0, 2.7)
Singapore 57.1 24.8 (21.4, 28.1) 2.5 (2.1, 2.8) 8.4 6.0 (4.8, 7.1) 0.5 (0.4, 0.6)
Republic of Korea 77.8 26.9 (17.6, 36.3) 37.8 (24.8, 51.1) 6.1a 2.1 (0.2, 4.0) 2.4 (0.2, 4.5)
Japan 79.6 27.7 (25.9, 29.5) 143.7 (134.3, 153.0) 9.1 3.7 (3.3, 4.2) 16.8 (15.0, 19.1)
East Asiansd 67.3 18.0 (15.9, 20.1) 869.4 (768.0, 970.9) 8.1 2.9 (2.0, 3.9) 122.8 (84.7, 165.1)
South Asiansd 42.8 11.7 (10.0, 13.4) 424.6 (362.9, 486.3) 1.6 0.3 (0.0, 0.6) 9.2 (0, 18.4)
All populationsd 58.6 15.8 (14.3, 17.2) 1,336.5 (1,209.7, 1,455.0) 5.8 3.3 (2.6, 4.0) 239.0 (188.3, 289.7)

Estimates are provided for populations age 45 y or older.

a

Because of the small sample size in the current study for these populations, data for smoking prevalence rates were obtained from other sources: Bangladeshi men and women: [12], Taiwanese women: [19], and Korean women: [34].

b

PARs were estimated using HRs derived from all South Asian cohorts combined because of unstable HR estimates using Bangladeshi data alone.

c

Mortality data for Taiwan were obtained from http://www.mohw.gov.tw/CHT/Ministry/Index.aspx.

d

PARs were estimated using weighted HRs and smoking prevalence of the study populations.

Thus, the number of deaths attributable to smoking in these populations may not be equal to the sum of the numbers of deaths from the countries in the population areas. East Asia: mainland China, Taiwan, Singapore, Republic of Korea, and Japan. South Asia: Bangladesh and India. All populations: all seven countries/regions listed above.

Among men aged ≥45 y, ∼11.4% (95% CI = 9.1%–13.8%), 30.5% (95% CI = 27.4%–33.6%), and 19.8% (95% CI = 14.8%–24.8%) of deaths due to CVD, cancer, and respiratory diseases, respectively, were attributable to tobacco smoking in 2004 (Table 8). Smoking-associated PARs for cause-specific mortality were also higher, in general, in Japan, Republic of Korea, and Singapore than in the other study populations. Overall, 60.5% (95% CI = 54.5%–66.4%) of lung cancer deaths in men were attributable to tobacco smoking. Data for women are presented for mainland China, Japan, and all East Asians combined, because of the small sample size for other groups. Smoking-associated PARs were much smaller in women than in men: 1.7% (95% CI = 0%–4.0%), 3.7% (95% CI = 2.4%–5.0%), and 4.6% (95% CI = 3.3%–5.8%) for deaths due to respiratory diseases, CVD, and cancer, respectively. Nevertheless, ∼16.7% (95% CI = 13.3%–20.0%) of lung-cancer deaths in East Asian women ≥45 y were attributable to tobacco smoking in 2004.

Table 8. Population-attributable risk and number of cause-specific deaths due to tobacco smoking in selected Asian populations.

Population CVD All Cancers Lung Cancer Respiratory Disease
PAR (Percent) Number of Deaths (in Thousands) PAR (Percent) Number of Deaths (in Thousands) PAR (Percent) Number of Deaths (in Thousands) PAR (Percent) Number of Deaths (in Thousands)
Men
Bangladesh 12.3a 16.4 (11.6, 21.3) 31.3a 10.8 (8.4, 13.1) 61.1a 8.6 (6.6, 10.5) 21.2a 6.4 (4.6, 8.3)
India 10.0 130.8 (91.5, 170.0) 26.1 85.6 (65.2, 105.6) 55.0 30.1 (22.1, 38.0) 17.3 69.2 (48.0, 90.0)
Mainland China 10.2 159.4 (101.5, 215.5) 32.0 325.1 (287.6, 361.7) 62.5 154.5 (143.6, 165.7) 19.0 141.0 (78.7, 202.6)
Taiwan 27.9 1.3 (0.8, 1.7) 26.2 7.1 (4.8, 9.4) 58.9 3.4 (3.1, 3.6) 24.9 1.1 (0.3, 1.9)
Singapore 19.8 0.7 (0.5, 0.9) 32.8 0.9 (0.8, 1.1) 59.3 0.5 (0.4, 0.5) 31.2 0.2 (0.1, 0.2)
Republic of Korea 17.3 6.1 (0, 14.3) 34.0 17.0 (10.5, 23.6) 66.5 8.4 (7.8, 8.9) 34.4 3.1 (0, 6.7)
Japan 21.7 31.4 (26.1, 36.9) 38.0 72.0 (66.3, 77.9) 67.0 29.0 (27.2, 30.8) 30.4 9.2 (7.5, 10.9)
East Asiansb 12.2 212.4 (156.7, 268.2) 32.7 410.6 (369.1, 453.2) 63.2 191.6 (177.6, 205.8) 21.0 164.1 (108.6, 220.4)
South Asiansb 10.0 144.5 (101.2, 189.3) 26.6 97.1 (74.5, 119.7) 55.5 38.6 (28.5, 48.7) 17.6 75.8 (52.6, 98.7)
All populationsb 11.4 363.3 (290.0, 439.7) 30.5 494.3 (444.0, 544.5) 60.5 225.5 (203.1, 247.5) 19.8 240.1 (179.5, 300.7)
Women
Mainland China 3.7 58.5 (42.7, 75.9) 4.3 25.5 (17.2, 34.4) 13.9 15.9 (12.0, 19.7) 1.5 11.7 (0, 32.8)
Japan 4.0 6.2 (5.5, 7.0) 4.3 5.4 (4.3, 6.5) 15.4 2.5 (1.9, 3.1) 3.5 0.7 (0.5, 1.0)
East Asiansb 3.7 66.3 (43.0, 89.6) 4.6 35.1 (25.2, 44.2) 16.7 23.0 (18.3, 27.5) 1.7 13.8 (0, 32.4)

Estimates are provided for populations age 45 y or older.

a

PARs were estimated using HRs derived from all South Asian cohorts combined because of unstable HR estimates using Bangladeshi data alone.

b

PARs were estimated using weighted HRs and smoking prevalence of the study populations.

Thus, the number of deaths attributable to smoking in these populations may not be equal to the sum of the numbers of deaths from countries in the population areas. East Asia: mainland China, Taiwan, Singapore, Republic of Korea, and Japan. South Asia: Bangladesh and India. All populations: all seven countries/regions listed above.

Discussion

Similar to studies conducted in Europe and North America [1][5],[9],[10], we found that tobacco smoking is associated with substantially elevated risk of total and cause-specific mortality. This study analyzed individual-level data from seven Asian countries/regions, using a uniform analytic approach, which enabled comparisons of smoking-associated HRs and PARs across these countries/regions. This study provides strong evidence that tobacco smoking is a major cause of death in Asia and underscores the importance and urgency of implementing comprehensive tobacco control programs for disease prevention in this populous continent.

Most smoking-associated RR estimates in this study were 1.3–1.5 for all-cause mortality, comparable to most estimates from previous studies conducted in Asia [14][21]. These RRs, however, are substantially lower than those from studies conducted in Europe and North America, where >2-fold elevated risk for all-cause mortality is typically reported for current smokers [1][3],[5],[9],[10]. Among specific causes of mortality evaluated in this study, lung cancer showed the strongest association with tobacco smoking, with estimated HRs of 3.0 to 4.0, approximately one-third of the risk observed in most studies conducted in Western countries [1][3],[5],[9],[10]. The smaller effect of smoking on mortality in Asia compared with Western countries could be partly explained by the fact that widespread tobacco smoking in most Asian countries began several decades later than in Europe and North America, and thus many Asian countries are still in the early stages of a tobacco epidemic; many smokers in the population started smoking tobacco at a late age and smoke a small number of cigarettes daily [3],[12]. In the British Doctors Study, a 1.6-fold elevated risk of all-cause mortality was observed among smokers in early years of follow-up (1951–1971) [26], close to the effect size estimated in this study. In later follow-up (1971–1991), the RR rose to 2.1. A recent Japanese study showed a clear birth-cohort effect: male smokers born before 1890 started smoking at a later age and smoked fewer cigarettes daily than those born in 1940–1945 [27]. As a result, the association of smoking with risk of all-cause mortality was weaker in the older cohort (RR = 1.24) than the younger cohort (RR = 1.92). Our study showed a clear dose–response relationship between pack-years of smoking and risk of all-cause and cause-specific mortality. It is likely that, with maturation of the tobacco epidemic in Asia and lack of effective tobacco control, more smokers will accumulate much higher pack-years of smoking, and, thus, smoking-associated RRs will rise, mirroring the trend in the US and Europe.

Several previous studies have estimated the burden of disease due to tobacco smoking in a specific Asian country/region [14],[16],[17],[19],[20] (Table S2). However, most previous estimates for smoking-associated RRs and PARs were derived from either a single cohort study [14],[19] or a retrospective case–control study [16][18]. Not all previous studies had detailed demographic and risk-factor information to adequately adjust for potential confounders when estimating risks. Three previous studies conducted in mainland China and Taiwan provided somewhat lower estimates of total male deaths due to smoking than our estimates, perhaps because these studies were conducted during even earlier stages of the tobacco epidemic in these populations, resulting in smaller PARs [14],[16],[19]. For India, however, the estimate of male deaths attributable to tobacco smoking from a previous study (20% of total male deaths) [17] was substantially higher than the estimate from our study (11.5% of total male deaths). To our knowledge, no study has been previously conducted in Bangladesh, the Republic of Korea, or Singapore; thus, our study provides, for the first time, direct estimates of deaths due to tobacco smoking in these countries. Despite methodological differences between this and previous studies, all studies conducted to date have shown that an alarming proportion of deaths are caused by tobacco smoking.

In this study, some estimates among women are unstable because of very low smoking prevalence. Although not all participating cohorts are representative of the general population, smoking-associated RRs estimated in this study, are, in general, comparable to those from previous studies. Furthermore, smoking-associated RRs estimated in multiple cohorts within the same country are, in general, comparable. It is difficult to find national survey data consistent with the definitions, time period, and age groups of our study for all seven countries/regions in our analysis. Many national surveys used a smaller sample than our study, providing unstable smoking prevalence estimates. Therefore, we chose to use smoking prevalence estimates from our own study to estimate PARs: smoking-associated RRs were estimated based on exposure history of the same group of individuals, which should provide better estimates of disease burden due to tobacco smoking in the study population than using data from external sources. Smoking prevalence has declined recently in several high-income Asian countries. However, given the long latency of chronic diseases, typically 15 y and longer, it is reasonable to use smoking prevalence rates assessed in the 1990s to estimate number of deaths due to tobacco smoking in 2004. As most of the cohort studies included in this study were conducted among adults aged ≥45 y, we were unable to estimate the impact of active tobacco smoking in people younger than 45 y old. Again, because of the long latency of chronic diseases, most of the smoking-related diseases tend to occur later in life.

We estimated smoking-associated PARs and numbers of deaths due to tobacco smoking in 2004. As many Asian countries, such as China and India, are still in the early stage of tobacco epidemics, the number of deaths due to tobacco smoking in more recent years in these countries is likely to be larger than that estimated in this study.

Data on secondhand tobacco-smoke exposure was not available in this study. Secondhand smoke has been linked to an elevated risk of multiple chronic diseases [2],[28],[29]. It has been estimated that approximately 603,000 deaths worldwide may be due to secondhand smoke [29]. We also were unable to evaluate smokeless tobacco, a risk factor for oral cancer and several other chronic diseases [30],[31]. Smokeless tobacco use is common in India and Bangladesh, especially among women in these countries. Some individuals who had secondhand tobacco-smoke exposure or used smokeless tobacco may be included in the reference group, which may result in an underestimate of the risk associated with active tobacco smoking. Furthermore, in our study, RRs associated with tobacco smoking were estimated primarily based on the time period from the early 1990s to the mid-2000s. Because smoking-associated risk of death is likely to increase with the maturation of the tobacco epidemic, the total number of deaths due to smoking in 2004 may be underestimated using this set of RRs. Therefore, the true impact of tobacco smoking on mortality in these Asian countries is likely to be even larger than estimated here. Despite some limitations mentioned above, our study provides perhaps the best estimates of tobacco-associated deaths to date in these Asian countries/regions.

Over the past 50 years, the landscape of tobacco smoking has changed dramatically around the world. Smoking prevalence has declined sharply in many high-income countries, resulting in a recent decrease in smoking-related deaths, particularly among men [3],[8]. Conversely, prevalence of tobacco use remains high in China, India, and other low- and middle-income countries. As the tobacco epidemic grows in these countries, we anticipate that an increasing number of deaths will be attributable to tobacco smoking in Asia in the coming years. Even in more well-developed Asian countries such as Japan and Republic of Korea, where smoking rates have recently declined, the full impact of tobacco smoking on mortality is unlikely to be seen soon because, as noted above, smokers in recent birth cohorts tend to smoke more and start smoking earlier, elevating their risk of smoking-associated deaths, and because of the long latency of the diseases associated with smoking, these deaths will not accrue immediately. Our study shows that tobacco smoking is a major cause of death in Asia, accounting for ∼1.6 million deaths of adults ≥45 y in 2004 in the seven countries/regions in this analysis. If the remaining 29% of the Asian population is experiencing a tobacco epidemic similar to that of these seven countries/regions, we estimate that, in 2004, >2 million deaths in Asia were attributable to tobacco smoking. Thus, of the 5 million deaths currently attributable to active tobacco smoking worldwide [32], nearly 45% occur in Asia. Our study provides sobering evidence that stresses the urgency of implementing comprehensive tobacco control programs in Asia, as recommended by the WHO Framework Convention on Tobacco Control [33]. Tobacco control should be among the top priorities in Asia to reduce the burden of disease.

Supporting Information

Table S1

Association of tobacco smoking status (former or current) with risk of death from all causes in selected study populations in Asia.

(DOC)

Table S2

Population-attributable risk and number of deaths due to smoking in major Asian populations estimated in previous studies.

(DOC)

Text S1

Descriptions of participating cohorts.

(DOC)

Acknowledgments

We thank Mary Jo Daly for clerical support in manuscript preparation and submission.

Abbreviations

CVD

cardiovascular disease

HR

hazard ratio

PAR

population attributable risk

RR

relative risk

Funding Statement

Participating cohort studies (funding sources) in the consortium are: Mumbai Cohort Study (Mumbai, funding sources: International Agency for Research on Cancer, Clinical Trials Service Unit/Oxford University, World Health Organization); Trivandrum Oral Cancer Screening (TOCS) Trial (funding sources: Association for International Cancer Research, St Andrews, UK; and Cancer Research UK); Health Effects of Arsenic Longitudinal Study [Bangladesh, funding sources: NIH (P42ES010349, R01CA102484, R01CA107431)]; China National Hypertension Survey Epidemiology Follow-up Study [CHEFS, funding sources: American Heart Association (9750612N), NHLBI (U01-HL072507), Chinese Academy of Medical Sciences]; Shanghai Cohort Study [SCS, funding sources: NIH (R01CA0403092, R01CA144034)]; Shanghai Men's Health Study [SMHS, funding sources: NIH (R01-CA82729)]; Shanghai Women's Health Study [SWHS, funding sources: NIH (R37-CA70867)]; Community-Based Cancer Screening Project [CBCSP, funding sources: National Science Council and Department of Health, Taiwan]; CardioVascular Disease risk FACtor Two-township Study [CVDFACTS, funding sources: Department of Health, Taiwan (DOH80-27, DOH81-021, DOH8202-1027, DOH83-TD-015, and DOH84-TD-006)]; Singapore Chinese Health Study [SCHS, funding sources: NIH (R01CA55069, R35CA53890, R01CA80205, R01CA144034)]; and Korea Multi-center Cancer Cohort [KMCC, funding sources: Ministry of Education, Science and Technology, Korea (2009-0087452), National Research Foundation of Korea (2009-0087452)]. The Radiation Effects Research Foundation (RERF), Hiroshima and Nagasaki, Japan is a private, nonprofit foundation funded by the Japanese Ministry of Health, Labour and Welfare (MHLW) and the U.S. Department of Energy (DOE), the latter in part through DOE Award DE-HS0000031 to the National Academy of Sciences. This publication was supported by RERF Research Protocol RP-A03-10. Other Japanese cohorts: Three Prefecture Cohort Study Aichi (3-Prefecture Aichi); Ibaraki Prefectural Health Study (JACC); Japan Public Health Center-based Prospective Study (JPHC1, JPHC2); Three Prefecture Cohort Study Miyagi (3-Prefecture Miyagi); Miyagi Cohort Study (Miyagi); and Ohsaki National Health Insurance Cohort Study (Ohsaki), are supported by the Grantin-aid for Cancer Research, the Grant for the Third Term Comprehensive Control Research for Cancer, the Grant for Health Services, the Grant for Medical Services for Aged and Health Promotion, the Grant for Comprehensive Research on Cardiovascular and Life-style Related Diseases from the Ministry of Health, Labour and Welfare, Japan, and the Grant for Scientific Research from the Ministry of Education, Culture, Sports, Science and Technology, Japan. Japan Public Health Center-Based Prospective Study is also supported by the National Cancer Center Research and Development Fund. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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Associated Data

This section collects any data citations, data availability statements, or supplementary materials included in this article.

Supplementary Materials

Table S1

Association of tobacco smoking status (former or current) with risk of death from all causes in selected study populations in Asia.

(DOC)

Table S2

Population-attributable risk and number of deaths due to smoking in major Asian populations estimated in previous studies.

(DOC)

Text S1

Descriptions of participating cohorts.

(DOC)


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