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1.  Tobacco Smoke, Indoor Air Pollution and Tuberculosis: A Systematic Review and Meta-Analysis 
PLoS Medicine  2007;4(1):e20.
Background
Tobacco smoking, passive smoking, and indoor air pollution from biomass fuels have been implicated as risk factors for tuberculosis (TB) infection, disease, and death. Tobacco smoking and indoor air pollution are persistent or growing exposures in regions where TB poses a major health risk. We undertook a systematic review and meta-analysis to quantitatively assess the association between these exposures and the risk of infection, disease, and death from TB.
Methods and Findings
We conducted a systematic review and meta-analysis of observational studies reporting effect estimates and 95% confidence intervals on how tobacco smoking, passive smoke exposure, and indoor air pollution are associated with TB. We identified 33 papers on tobacco smoking and TB, five papers on passive smoking and TB, and five on indoor air pollution and TB. We found substantial evidence that tobacco smoking is positively associated with TB, regardless of the specific TB outcomes. Compared with people who do not smoke, smokers have an increased risk of having a positive tuberculin skin test, of having active TB, and of dying from TB. Although we also found evidence that passive smoking and indoor air pollution increased the risk of TB disease, these associations are less strongly supported by the available evidence.
Conclusions
There is consistent evidence that tobacco smoking is associated with an increased risk of TB. The finding that passive smoking and biomass fuel combustion also increase TB risk should be substantiated with larger studies in future. TB control programs might benefit from a focus on interventions aimed at reducing tobacco and indoor air pollution exposures, especially among those at high risk for exposure to TB.
Evidence from a number of studies suggest that tobacco smoking, environmental tobacco smoke, and indoor air pollution from biomass fuels is associated with an increased risk of tuberculosis.
Editors' Summary
Background.
Tobacco smoking has been identified by the World Health Organization as one of the leading causes of death worldwide. Smokers are at higher risk than nonsmokers for a very wide variety of illnesses, many of which are life-threatening. Inhaling tobacco smoke, whether this is active (when an individual smokes) or passive (when an individual is exposed to cigarette smoke in their environment) has also been associated with tuberculosis (TB). Many people infected with the TB bacterium never develop disease, but it is thought that people infected with TB who also smoke are far more likely to develop the symptoms of disease, and to have worse outcomes when they do.
Why Was This Study Done?
The researchers were specifically interested in the link between smoking and TB. They wanted to try to work out the overall increase in risk for getting TB in people who smoke, as compared with people who do not smoke. In this study, the researchers wanted to separately study the risks for different types of exposure to smoke, so, for example, what the risks were for people who actively smoke as distinct from people who are exposed to smoke from others. The researchers also wanted to calculate the association between TB and exposure to indoor pollution from burning fuels such as wood and charcoal.
What Did the Researchers Do and Find?
In carrying out this study, the researchers wanted to base their conclusions on all the relevant information that was already available worldwide. Therefore they carried out a systematic review. A systematic review involves setting out the research question that is being asked and then developing a search strategy to find all the meaningful evidence relating to the particular question under study. For this systematic review, the researchers wanted to find all published research in the biomedical literature that looked at human participants and dealt with the association between active smoking, passive smoking, indoor air pollution and TB. Studies were included if they were published in English, Russian, or Chinese, and included enough data for the researchers to calculate a number for the increase in TB risk. The researchers initially found 1,397 research studies but then narrowed that down to 38 that fit their criteria. Then specific pieces of data were extracted from each of those studies and in some cases the researchers combined data to produce overall calculations for the increase in TB risk. Separate assessments were done for different aspects of “TB risk,” namely, TB infection, TB disease, and mortality from TB. The data showed an approximately 2-fold increase in risk of TB infection among smokers as compared with nonsmokers. The researchers found that all studies evaluating the link between smoking and TB disease or TB mortality showed an association, but they did not combine these data together because of wide potential differences between the studies. Finally, all studies looking at passive smoking found an association with TB, as did some of those examining the link with indoor air pollution.
What Do These Findings Mean?
The findings here show that smoking is associated with an increased risk of TB infection, disease, and deaths from TB. The researchers found much more data on the risks for active smoking than on passive smoking or indoor air pollution. Tobacco smoking is increasing in many countries where TB is already a problem. These results therefore suggest that it is important for health policy makers to further develop strategies for controlling tobacco use in order to reduce the impact of TB worldwide.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0040020
The World Health Organization (WHO)'s Tobacco Free Initiative provides resources on research and policy related to tobacco control, its network of initiatives, and other relevant information
WHO also has a tuberculosis minisite
The US National Library of Medicine's MedLinePlus provides a set of links and resources about smoking, including news, overviews, recent research, statistics, and others
The Health Consequences of Smoking: A Report of the Surgeon General provides information on the health consequences of smoking
Tobacco Country Profiles provides information on smoking in different countries
doi:10.1371/journal.pmed.0040020
PMCID: PMC1769410  PMID: 17227135
2.  Active and Passive Cigarette Smoking and the Risk of Cervical Neoplasia 
Obstetrics and gynecology  2005;105(1):174-181.
OBJECTIVE
Evidence links active cigarette smoking to cervical neoplasia, but much less is known about the role of passive smoking. Using a prospective cohort design, we examined personal cigarette smoking and household passive smoke exposure in relation to the risk of cervical neoplasia.
METHODS
Cohorts were established based on data collected on the smoking status of all household members during private censuses of Washington County, Maryland in 1963 (n = 24,792) and 1975 (n = 26,381). Using the Washington County Cancer Registry, the occurrence of cervical neoplasia in the two cohorts was ascertained from 1963–1978 and from 1975–1994. Poisson regression models were fitted to estimate the relative risk of developing cervical neoplasia associated with active and passive smoking in both cohorts. The referent category for all comparisons was never smokers not exposed to passive smoking.
RESULTS
The adjusted relative risk and 95% confidence limits for passive smoking was 2.1 (1.3, 3.3) in the 1963 cohort and 1.4 (0.8, 2.4) in the 1975 cohort. The adjusted relative risk and 95% confidence limits for current smoking were 2.6 (1.7, 4.1) and 1.7 (1.1, 2.6) in the 1963 and 1975 cohort, respectively.
CONCLUSION
The associations were in the direction of increased risk for both passive smoking and current active smoking in both the 1963 and 1975 cohorts, but were stronger in the 1963 cohort. The results of this long-term, prospective cohort study corroborate the association between active cigarette smoking and cervical neoplasia and provide evidence that passive smoking is a risk factor for cervical neoplasia.
doi:10.1097/01.AOG.0000148268.43584.03
PMCID: PMC3064987  PMID: 15625160
3.  Active and passive smoking and the risk of breast cancer in women aged 36–45 years: a population based case–control study in the UK 
British Journal of Cancer  2007;97(3):434-439.
Active smoking has little or no effect on breast cancer risk but some investigators have suggested that passive smoking and its interaction with active smoking may be associated with an increased risk. In a population based case–control study of breast cancer in women aged 36–45 years at diagnosis, information on active smoking, passive smoking in the home, and other factors, was collected at interview from 639 cases and 640 controls. Women were categorised jointly by their active and passive smoking exposure. Among never smoking controls, women who also reported no passive smoking exposure were significantly more likely to be nulliparous and to be recent users of oral contraceptives. Among those never exposed to passive smoking, there was no significant association between active smoking and breast cancer, relative risk (RR) of 1.12 (95% confidence interval (CI) 0.72–1.73) for past smokers and RR of 1.19 (95% CI 0.72–1.95) for current smokers, nor was there an association with age started, duration or intensity of active smoking. Compared with women who were never active nor passive smokers, there was no significant association between passive smoking in the home and breast cancer risk in never smokers, RR of 0.89 (95% CI 0.64–1.25), in past smokers, RR of 1.09 (95% CI 0.75–1.56), or in current smokers, RR of 0.93 (95% CI 0.67–1.30). There was no trend with increasing duration of passive smoking and there was no heterogeneity among any of the subgroups examined. In this study, there was no evidence of an association between either active smoking or passive smoking in the home and risk of breast cancer.
doi:10.1038/sj.bjc.6603859
PMCID: PMC2360334  PMID: 17579618
breast cancer; smoking; passive smoking; case-control study
4.  Active or Passive Exposure to Tobacco Smoking and Allergic Rhinitis, Allergic Dermatitis, and Food Allergy in Adults and Children: A Systematic Review and Meta-Analysis 
PLoS Medicine  2014;11(3):e1001611.
In a systematic review and meta-analysis, Bahi Takkouche and colleagues examine the associations between exposure to tobacco smoke and allergic disorders in children and adults.
Please see later in the article for the Editors' Summary
Background
Allergic rhinitis, allergic dermatitis, and food allergy are extremely common diseases, especially among children, and are frequently associated to each other and to asthma. Smoking is a potential risk factor for these conditions, but so far, results from individual studies have been conflicting. The objective of this study was to examine the evidence for an association between active smoking (AS) or passive exposure to secondhand smoke and allergic conditions.
Methods and Findings
We retrieved studies published in any language up to June 30th, 2013 by systematically searching Medline, Embase, the five regional bibliographic databases of the World Health Organization, and ISI-Proceedings databases, by manually examining the references of the original articles and reviews retrieved, and by establishing personal contact with clinical researchers. We included cohort, case-control, and cross-sectional studies reporting odds ratio (OR) or relative risk (RR) estimates and confidence intervals of smoking and allergic conditions, first among the general population and then among children.
We retrieved 97 studies on allergic rhinitis, 91 on allergic dermatitis, and eight on food allergy published in 139 different articles. When all studies were analyzed together (showing random effects model results and pooled ORs expressed as RR), allergic rhinitis was not associated with active smoking (pooled RR, 1.02 [95% CI 0.92–1.15]), but was associated with passive smoking (pooled RR 1.10 [95% CI 1.06–1.15]). Allergic dermatitis was associated with both active (pooled RR, 1.21 [95% CI 1.14–1.29]) and passive smoking (pooled RR, 1.07 [95% CI 1.03–1.12]). In children and adolescent, allergic rhinitis was associated with active (pooled RR, 1.40 (95% CI 1.24–1.59) and passive smoking (pooled RR, 1.09 [95% CI 1.04–1.14]). Allergic dermatitis was associated with active (pooled RR, 1.36 [95% CI 1.17–1.46]) and passive smoking (pooled RR, 1.06 [95% CI 1.01–1.11]). Food allergy was associated with SHS (1.43 [1.12–1.83]) when cohort studies only were examined, but not when all studies were combined.
The findings are limited by the potential for confounding and bias given that most of the individual studies used a cross-sectional design. Furthermore, the studies showed a high degree of heterogeneity and the exposure and outcome measures were assessed by self-report, which may increase the potential for misclassification.
Conclusions
We observed very modest associations between smoking and some allergic diseases among adults. Among children and adolescents, both active and passive exposure to SHS were associated with a modest increased risk for allergic diseases, and passive smoking was associated with an increased risk for food allergy. Additional studies with detailed measurement of exposure and better case definition are needed to further explore the role of smoking in allergic diseases.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
The immune system protects the human body from viruses, bacteria, and other pathogens. Whenever a pathogen enters the body, immune system cells called T lymphocytes recognize specific molecules on its surface and release chemical messengers that recruit and activate other types of immune cells, which then attack the pathogen. Sometimes, however, the immune system responds to harmless materials (for example, pollen; scientists call these materials allergens) and triggers an allergic disease such as allergic rhinitis (inflammation of the inside of the nose; hay fever is a type of allergic rhinitis), allergic dermatitis (also known as eczema, a disease characterized by dry, itchy patches on the skin), and food allergy. Recent studies suggest that all these allergic (atopic) diseases are part of a continuous state called the “atopic march” in which individuals develop allergic diseases in a specific sequence that starts with allergic dermatitis during infancy, and progresses to food allergy, allergic rhinitis, and finally asthma (inflammation of the airways).
Why Was This Study Done?
Allergic diseases are extremely common, particularly in children. Allergic rhinitis alone affects 10%–30% of the world's population and up to 40% of children in some countries. Moreover, allergic diseases are becoming increasingly common. Allergic diseases affect the quality of life of patients and are financially costly to both patients and health systems. It is important, therefore, to identify the factors that cause or potentiate their development. One potential risk factor for allergic diseases is active or passive exposure to tobacco smoke. In some countries up to 80% of children are exposed to second-hand smoke so, from a public health point of view, it would be useful to know whether exposure to tobacco smoke is associated with the development of allergic diseases. Here, the researchers undertake a systematic review (a study that uses predefined criteria to identify all the research on a given topic) and a meta-analysis (a statistical approach for combining the results of several studies) to investigate this issue.
What Did the Researchers Do and Find?
The researchers identified 196 observational studies (investigations that observe outcomes in populations without trying to affect these outcomes in any way) that examined the association between smoke exposure and allergic rhinitis, allergic dermatitis, or food allergy. When all studies were analyzed together, allergic rhinitis was not associated with active smoking but was slightly associated with exposure to second-hand smoke. Specifically, compared to people not exposed to second-hand smoke, the pooled relative risk (RR) of allergic rhinitis among people exposed to second-hand smoke was 1.10 (an RR of greater than 1 indicates an increased risk of disease development in an exposed population compared to an unexposed population). Allergic dermatitis was associated with both active smoking (RR = 1.21) and exposure to second-hand smoke (RR = 1.07). In the populations of children and adolescents included in the studies, allergic rhinitis was associated with both active smoking and exposure to second-hand smoke (RRs of 1.40 and 1.09, respectively), as was allergic dermatitis (RRs of 1.36 and 1.06, respectively). Finally food allergy was associated with exposure to second-hand smoke (RR = 1.43) when cohort studies (a specific type of observational study) only were examined but not when all the studies were combined.
What Do These Findings Mean?
These findings provide limited evidence for a weak association between smoke exposure and allergic disease in adults but suggest that both active and passive smoking are associated with a modestly increased risk of allergic diseases in children and adolescents. The accuracy of these findings may be affected by the use of questionnaires to assess smoke exposure and allergic disease development in most of the studies in the meta-analysis and by the possibility that individuals exposed to smoke may have shared other characteristics that were actually responsible for their increased risk of allergic diseases. To shed more light on the role of smoking in allergic diseases, additional studies are needed that accurately measure exposure and outcomes. However, the present findings suggest that, in countries where many people smoke, 14% and 13% of allergic rhinitis and allergic dermatitis, respectively, among children may be attributable to active smoking. Thus, the elimination of active smoking among children and adolescents could prevent one in seven cases of allergic rhinitis and one in eight cases of allergic dermatitis in such countries.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001611.
The UK National Health Service Choices website provides information about allergic rhinitis, hay fever (including personal stories), allergic dermatitis (including personal stories), and food allergy (including personal stories)
The US National Institute of Allergy and Infectious Disease provides information about allergic diseases
The UK not-for-profit organization Allergy UK provides information about all aspects of allergic diseases and a description of the atopic march
MedlinePlus encyclopedia has pages on allergic rhinitis and allergic dermatitis (in English and Spanish)
MedlinePlus provides links to further resources about allergies, eczema, and food allergy (in English and Spanish)
doi:10.1371/journal.pmed.1001611
PMCID: PMC3949681  PMID: 24618794
5.  Passive smoking as well as active smoking increases the risk of acute stroke 
Tobacco Control  1999;8(2):156-160.
OBJECTIVE—To estimate the relative risk of stroke associated with exposure to environmental tobacco smoke (ETS, passive smoking) and to estimate the risk of stroke associated with current smoking (active smoking) using the traditional baseline group (never-smokers) and a baseline group that includes lifelong non-smokers and long-term (>10 years) ex-smokers who have not been exposed to ETS.
DESIGN AND SETTING—Population-based case-control study in residents of Auckland, New Zealand.
SUBJECTS—Cases were obtained from the Auckland stroke study, a population-based register of acute stroke. Controls were obtained from a cross-sectional survey of major cardiovascular risk factors measured in the same population. A standard questionaire was administered to patients and controls by trained nurse interviewers.
RESULTS—Information was available for 521 patients with first-ever acute stroke and 1851 community controls aged 35-74 years. After adjusting for potential confounders (age, sex, history of hypertension, heart disease, and diabetes) using logistic regression, exposure to ETS among non-smokers and long-term ex-smokers was associated with a significantly increased risk of stroke (odds ratio (OR) = 1.82; 95% confidence interval (95% CI) = 1.34 to 2.49). The risk was significant in men (OR = 2.10; 95% CI = 1.33 to 3.32) and women (OR = 1.66; 95% CI = 1.07 to 2.57). Active smokers had a fourfold risk of stroke compared with people who reported they had never smoked cigarettes (OR = 4.14; 95% CI = 3.04 to 5.63); the risk increased when active smokers were compared with people who had never smoked or had quit smoking more than 10 years earlier and who were not exposed to ETS (OR = 6.33; 95% CI = 4.50 to 8.91).
CONCLUSIONS—This study is one of the few to investigate the association between passive smoking and the risk of acute stroke. We found a significantly increased risk of stroke in men and in women. This study also confirms the higher risk of stroke in men and women who smoke cigarettes compared with non-smokers. The stroke risk increases further when those who have been exposed to ETS are excluded from the non-smoking reference group. These findings also suggest that studies investigating the adverse effects of smoking will underestimate the risk if exposure to ETS is not taken into account.


Keywords: environmental tobacco smoke; stroke; smoking-attributable diseases
PMCID: PMC1759715  PMID: 10478399
6.  Reproductive Factors and Non-Hodgkin Lymphoma Risk in the California Teachers Study 
PLoS ONE  2009;4(12):e8135.
Background
Non-Hodgkin lymphoma (NHL) is a malignancy etiologically linked to immunomodulatory exposures and disorders. Endogenous female sex hormones may modify immune function and influence NHL risk. Few studies have examined associations between reproductive factors, which can serve as surrogates for such hormonal exposures, and NHL risk by subtype.
Methodology/Principal Findings
Women in the California Teachers Study cohort provided detailed data in 1995–1996 on reproductive history. Follow-up through 2007 identified 574 women with incident B-cell NHL. Hazard rate ratios (RR) and 95% confidence intervals (CI) were estimated using Cox proportional hazards models to assess associations between reproductive factors and all B-cell NHL combined, diffuse large B-cell lymphomas, follicular lymphomas, and B-cell chronic lymphocytic leukemias/small lymphocytic lymphomas. Pregnancy was marginally associated with lower risk of B-cell NHL (RR = 0.84, 95% CI = 0.68–1.04). Much of the reduction in risk was observed after one full-term pregnancy relative to nulligravid women (RR = 0.75, 95% CI = 0.54–1.06; P for trend <0.01), particularly for diffuse large B-cell lymphomas (P for trend = 0.13), but not among women who had only incomplete pregnancies. Age at first full-term pregnancy was marginally inversely associated with B-cell NHL risk overall (P for trend = 0.08) and for diffuse large B-cell lymphomas (P for trend = 0.056). Breast feeding was not associated with B-cell NHL risk overall or by subtype.
Conclusions
Full-term pregnancy and early age at first full-term pregnancy account for most of the observed reduction in B-cell NHL risk associated with gravidity. Pregnancy-related hormonal exposures, including prolonged and high-level exposure to progesterone during a full-term pregnancy may inhibit development of B-cell NHL.
doi:10.1371/journal.pone.0008135
PMCID: PMC2780313  PMID: 19956586
7.  Burden of Total and Cause-Specific Mortality Related to Tobacco Smoking among Adults Aged ≥45 Years in Asia: A Pooled Analysis of 21 Cohorts 
PLoS Medicine  2014;11(4):e1001631.
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
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
doi:10.1371/journal.pmed.1001631
PMCID: PMC3995657  PMID: 24756146
8.  Non-Hodgkin Lymphoma Risk and Insecticide, Fungicide and Fumigant Use in the Agricultural Health Study 
PLoS ONE  2014;9(10):e109332.
Farming and pesticide use have previously been linked to non-Hodgkin lymphoma (NHL), chronic lymphocytic leukemia (CLL) and multiple myeloma (MM). We evaluated agricultural use of specific insecticides, fungicides, and fumigants and risk of NHL and NHL-subtypes (including CLL and MM) in a U.S.-based prospective cohort of farmers and commercial pesticide applicators. A total of 523 cases occurred among 54,306 pesticide applicators from enrollment (1993–97) through December 31, 2011 in Iowa, and December 31, 2010 in North Carolina. Information on pesticide use, other agricultural exposures and other factors was obtained from questionnaires at enrollment and at follow-up approximately five years later (1999–2005). Information from questionnaires, monitoring, and the literature were used to create lifetime-days and intensity-weighted lifetime days of pesticide use, taking into account exposure-modifying factors. Poisson and polytomous models were used to calculate relative risks (RR) and 95% confidence intervals (CI) to evaluate associations between 26 pesticides and NHL and five NHL-subtypes, while adjusting for potential confounding factors. For total NHL, statistically significant positive exposure-response trends were seen with lindane and DDT. Terbufos was associated with total NHL in ever/never comparisons only. In subtype analyses, terbufos and DDT were associated with small cell lymphoma/chronic lymphocytic leukemia/marginal cell lymphoma, lindane and diazinon with follicular lymphoma, and permethrin with MM. However, tests of homogeneity did not show significant differences in exposure-response among NHL-subtypes for any pesticide. Because 26 pesticides were evaluated for their association with NHL and its subtypes, some chance finding could have occurred. Our results showed pesticides from different chemical and functional classes were associated with an excess risk of NHL and NHL subtypes, but not all members of any single class of pesticides were associated with an elevated risk of NHL or NHL subtypes. These findings are among the first to suggest links between DDT, lindane, permethrin, diazinon and terbufos with NHL subtypes.
doi:10.1371/journal.pone.0109332
PMCID: PMC4206281  PMID: 25337994
9.  Passive smoking and chronic obstructive pulmonary disease: cross-sectional analysis of data from the Health Survey for England 
BMJ Open  2011;1(2):e000153.
Objectives
There is increasing evidence that passive smoking is associated with chronic respiratory diseases, but its association with chronic obstructive pulmonary disease (COPD) requires more study. In this cross-sectional analysis of data from 3 years of the Health Survey for England, the association between passive smoking exposure and risk of COPD is evaluated.
Design
Cross-sectional analysis of the 1995, 1996 and 2001 Health Surveys for England including participants of white ethnicity, aged 40+ years with valid lung function data. COPD was defined using the lower limit of normal spirometric criteria for airflow obstruction. Standardised questions elicited self-reported information on demography, smoking history, ethnicity, occupation, asthma and respiratory symptoms (dyspnoea, chronic cough, chronic phlegm, wheeze). Passive smoking was measured by self-report of hours of exposure to cigarette smoke per week.
Results
Increasing passive smoke exposure was independently associated with increased risk of COPD, with adjusted OR 1.05 (95% CI 0.93 to 1.18) for 1–19 h and OR 1.18 (95% CI 1.01 to 1.39) for 20 or more hours of exposure per week. Similar patterns (although attenuated and non-significant) were observed among never smokers. More marked dose–response relationships were observed between passive smoking exposure and respiratory symptoms, but the most marked effects were on the development of clinically significant COPD (airflow obstruction plus symptoms), where the risk among never smokers was doubled (OR 1.98 (95% CI 1.03 to 3.79)) if exposure exceeded 20 h/week.
Conclusion
This analysis adds weight to the evidence suggesting an association between passive smoking exposure and COPD.
Article summary
Article focus
Passive exposure to cigarette smoke is established as an important independent risk factor for the development of chronic conditions such as heart disease and lung cancer.
Although there is growing evidence implicating passive smoking in asthma and other respiratory diseases, the evidence for its effect on chronic obstructive pulmonary disease (COPD) is inconsistent.
Using cross-sectional data from the annual Health Survey for England, we examined the association between self-reported exposure to passive smoking and COPD.
Key messages
We have demonstrated a significant dose–response relationship between hours of exposure to passive smoking and increasing risk of COPD.
The most marked effects were observed on the development of clinically significant COPD (airflow obstruction plus symptoms), where the risk among never smokers was doubled (OR 1.98 (95% CI 1.03 to 3.79)) if exposure exceeded 20 h/week.
Passive smoking is prevalent worldwide, and even after the 2007 public smoking ban in the UK, 20% of the adult English population are still exposed to up to 20 h of passive smoking per week, with 5% exposed to more than 20 h/week; further measures are needed to investigate and reduce exposures in the home and elsewhere.
Strengths and limitations of this study
Our study has the advantage of being a large sample representative of the English population (>21 000 participants), conducted over 3 separate years, with a standardised protocol and objective measure of lung function.
However, due to the cross-sectional nature of the design, temporal associations cannot necessarily be inferred.
The Health Survey for England was not designed for the specific analyses presented in this paper, and thus some of the measures are crude.
Self-reported passive smoke exposure is only a proxy for true exposure levels, but is accepted as the most practical method of assessment.
doi:10.1136/bmjopen-2011-000153
PMCID: PMC3191589  PMID: 22021874
10.  Active and passive smoking and development of glucose intolerance among young adults in a prospective cohort: CARDIA study 
BMJ : British Medical Journal  2006;332(7549):1064-1069.
Objective To assess whether active and passive smokers are more likely than non-smokers to develop clinically relevant glucose intolerance or diabetes.
Design Coronary artery risk development in young adults (CARDIA) is a prospective cohort study begun in 1985-6 with 15 years of follow-up.
Setting Participants recruited from Birmingham, Alabama; Chicago, Illinois; Minneapolis, Minnesota; and Oakland, California, USA.
Participants Black and white men and women aged 18-30 years with no glucose intolerance at baseline, including 1386 current smokers, 621 previous smokers, 1452 never smokers with reported exposure to secondhand smoke (validated by serum cotinine concentrations 1-15 ng/ml), and 1113 never smokers with no exposure to secondhand smoke.
Main outcome measure Time to development of glucose intolerance (glucose ≥ 100 mg/dl or taking antidiabetic drugs) during 15 years of follow-up.
Results Median age at baseline was 25, 55% of participants were women, and 50% were African-American. During follow-up, 16.7% of participants developed glucose intolerance. A graded association existed between smoking exposure and the development of glucose intolerance. The 15 year incidence of glucose intolerance was highest among smokers (21.8%), followed by never smokers with passive smoke exposure (17.2%), and then previous smokers (14.4%); it was lowest for never smokers with no passive smoke exposure (11.5%). Current smokers (hazard ratio 1.65, 95% confidence interval 1.27 to 2.13) and never smokers with passive smoke exposure (1.35, 1.06 to 1.71) remained at higher risk than never smokers without passive smoke exposure after adjustment for multiple baseline sociodemographic, biological, and behavioural factors, but risk in previous smokers was similar to that in never smokers without passive smoke exposure.
Conclusion These findings support a role of both active and passive smoking in the development of glucose intolerance in young adulthood.
doi:10.1136/bmj.38779.584028.55
PMCID: PMC1458534  PMID: 16603565
11.  Association of active and passive smoking with risk of breast cancer among postmenopausal women: a prospective cohort study 
Objective To examine the association between smoking and risk of invasive breast cancer using quantitative measures of lifetime passive and active smoking exposure among postmenopausal women.
Design Prospective cohort study.
Setting 40 clinical centres in the United States.
Participants 79 990 women aged 50–79 enrolled in the Women’s Health Initiative Observational Study during 1993–8.
Main outcome measures Self reported active and passive smoking, pathologically confirmed invasive breast cancer.
Results In total, 3520 incident cases of invasive breast cancer were identified during an average of 10.3 years of follow-up. Compared with women who had never smoked, breast cancer risk was elevated by 9% among former smokers (hazard ratio 1.09 (95% CI 1.02 to 1.17)) and by 16% among current smokers (hazard ratio 1.16 (1.00 to 1.34)). Significantly higher breast cancer risk was observed in active smokers with high intensity and duration of smoking, as well as with initiation of smoking in the teenage years. The highest breast cancer risk was found among women who had smoked for ≥50 years or more (hazard ratio 1.35 (1.03 to1.77) compared with all lifetime non-smokers, hazard ratio 1.45 (1.06 to 1.98) compared with lifetime non-smokers with no exposure to passive smoking). An increased risk of breast cancer persisted for up to 20 years after smoking cessation. Among women who had never smoked, after adjustment for potential confounders, those with the most extensive exposure to passive smoking (≥10 years’ exposure in childhood, ≥20 years’ exposure as an adult at home, and ≥10 years’ exposure as an adult at work) had a 32% excess risk of breast cancer compared with those who had never been exposed to passive smoking (hazard ratio 1.32 (1.04 to 1.67)). However, there was no significant association in the other groups with lower exposure and no clear dose response to cumulative passive smoking exposure.
Conclusions Active smoking was associated with an increase in breast cancer risk among postmenopausal women. There was also a suggestion of an association between passive smoking and increased risk of breast cancer.
doi:10.1136/bmj.d1016
PMCID: PMC3047002  PMID: 21363864
12.  Smoking, Alcohol Use, Obesity, and Overall Survival from Non-Hodgkin Lymphoma: A Population-Based Study 
Cancer  2010;116(12):2993-3000.
BACKGROUND
Smoking, alcohol use, and obesity appear to increase the risk of developing non-Hodgkin lymphoma (NHL), but few studies have assessed their impact on NHL prognosis.
METHODS
We evaluated the association of pre-diagnosis cigarette smoking, alcohol use, and body mass index (BMI) on overall survival in 1,286 patients enrolled through population-based registries in the United States from 1998–2000. Hazard Ratios (HR) and 95% confidence intervals (CI) were estimated using Cox regression, adjusting for clinical and demographic factors.
RESULTS
Through 2007, 442 patients died (34%), and the median follow-up on living patients was 7.7 years. Compared to never smokers, former (HR=1.59; 95% CI 1.12–2.26) and current (HR=1.50; 95% CI 0.97–2.29) smokers had poorer survival, and poorer survival was positively associated with smoking duration, number of cigarettes smoked per day, pack-years of smoking, and shorter time since quitting (all p-trend<0.01). Alcohol use was associated with poorer survival (p-trend=0.03); compared to non-users, those drinking more than 43.1 grams/week (median of intake among drinkers) had poorer survival (HR=1.55; 95% CI 1.06–2.27) while those drinkers consuming less than this amount showed no survival disadvantage (HR=1.13; 95% CI 0.75–1.71). Greater body mass index was associated with poorer survival (p-trend=0.046), but the survival disadvantage was only seen among obese individuals (HR=1.32 for BMI ≥30 versus 20–24.9 kg/m2; 95% CI 1.02–1.70). These results held for lymphoma-specific survival and were broadly similar for DLBCL and follicular lymphoma.
CONCLUSIONS
NHL patients who smoked, consumed alcohol or were obese prior to diagnosis had a poorer overall and lymphoma-specific survival.
doi:10.1002/cncr.25114
PMCID: PMC2889918  PMID: 20564404
alcohol; non-Hodgkin lymphoma; obesity; smoking; survival
13.  Smoking and high-risk mammographic parenchymal patterns: a case-control study 
Breast Cancer Research  1999;2(1):59-63.
Current smoking was strongly and inversely associated with high-risk patterns, after adjustment for concomitant risk factors. Relative to never smokers, current smokers were significantly less likely to have a high-risk pattern. Similar results were obtained when the analysis was confined to postmenopausal women. Past smoking was not related to the mammographic parenchymal patterns. The overall effect in postmenopausal women lost its significance when adjusted for other risk factors for P2/DY patterns that were found to be significant in the present study, although the results are still strongly suggestive. The present data indicate that adjustment for current smoking status is important when evaluating the relationship between mammographic parenchymal pattern and breast cancer risk. They also indicate that smoking is a prominent potential confounder when analyzing effects of other risk factors such as obesity-related variables. It appears that parenchymal patterns may act as an informative biomarker of the effect of cigarette smoking on breast cancer risk.
Introduction:
Overall, epidemiological studies [1,2,3,4] have reported no substantial association between cigarette smoking and the risk of breast cancer. Some studies [5,6,7] reported a significant increase of breast cancer risk among smokers. In recent studies that addressed the association between breast cancer and cigarette smoking, however, there was some suggestion of a decreased risk [8,9,10], especially among current smokers, ranging from approximately 10 to 30% [9,10]. Brunet et al [11] reported that smoking might reduce the risk of breast cancer by 44% in carriers of BRCA1 or BRCA2 gene mutations. Wolfe [12] described four different mammographic patterns created by variations in the relative amounts of fat, epithelial and connective tissue in the breast, designated N1, P1, P2 and DY. Women with either P2 or DY pattern are considered at greater risk for breast cancer than those with N1 or P1 pattern [12,13,14,15]. There are no published studies that assessed the relationship between smoking and mammographic parenchymal patterns.
Aims:
To evaluate whether mammographic parenchymal patterns as classified by Wolfe, which have been positively associated with breast cancer risk, are affected by smoking. In this case-control study, nested within the European Prospective Investigation on Cancer in Norfolk (EPIC-Norfolk) cohort [16], the association between smoking habits and mammographic parenchymal patterns are examined. The full results will be published elsewhere.
Methods:
Study subjects were members of the EPIC cohort in Norwich who also attended the prevalence screening round at the Norwich Breast Screening Centre between November 1989 and December 1997, and were free of breast cancer at that screening. Cases were defined as women with a P2/DY Wolfe's mammographic parenchymal pattern on the prevalence screen mammograms. A total of 203 women with P2/DY patterns were identified as cases and were individually matched by date of birth (within 1 year) and date of prevalence screening (within 3 months) with 203 women with N1/P1 patterns who served as control individuals.
Two views, the mediolateral and craniocaudal mammograms, of both breasts were independently reviewed by two of the authors (ES and RW) to determine the Wolfe mammographic parenchymal pattern.
Considerable information on health and lifestyle factors was available from the EPIC Health and Lifestyle Questionnaire [16]. In the present study we examined the subjects' personal history of benign breast diseases, menstrual and reproductive factors, oral contraception and hormone replacement therapy, smoking, and anthropometric information such as body mass index and waist:hip ratio.
Odds ratios (ORs) and their 95% confidence intervals (CIs) were calculated by conditional logistic regression [17], and were adjusted for possible confounding factors.
Results:
The characteristics of the cases and controls are presented in Table 1. Cases were leaner than controls. A larger percentage of cases were nulliparous, premenopausal, current hormone replacement therapy users, had a personal history of benign breast diseases, and had had a hysterectomy. A larger proportion of controls had more than three births and were current smokers.
Table 2 shows the unadjusted and adjusted OR estimates for Wolfe's high-risk mammographic parenchymal patterns and smoking in the total study population and in postmenopausal women separately. Current smoking was strongly and inversely associated with high-risk patterns, after adjustment for concomitant risk factors. Relative to never smokers, current smokers were significantly less likely to have a high-risk pattern (OR 0.37, 95% CI 0.14-0.94). Similar results were obtained when the analysis was confined to postmenopausal women. Past smoking was not related to mammographic parenchymal patterns. The overall effect in postmenopausal women lost its significance when adjusted for other risk factors for P2/DY patterns that were found to be significant in the present study, although the results were still strongly suggestive. There was no interaction between cigarette smoking and body mass index.
Discussion:
In the present study we found a strong inverse relationship between current smoking and high-risk mammographic parenchymal patterns of breast tissue as classified by Wolfe [12]. These findings are not completely unprecedented; Greendale et al [18] found a reduced risk of breast density in association with smoking, although the magnitude of the reduction was unclear. The present findings suggest that this reduction is large.
Recent studies [9,10] have suggested that breast cancer risk may be reduced among current smokers. In a multicentre Italian case-control study, Braga et al [10] found that, relative to nonsmokers, current smokers had a reduced risk of breast cancer (OR 0.84, 95% CI 0.7-1.0). These findings were recently supported by Gammon et al [9], who reported that breast cancer risk in younger women (younger than 45 years) may be reduced among current smokers who began smoking at an early age (OR 0.59, 95% CI 0.41-0.85 for age 15 years or younger) and among long-term smokers (OR 0.70, 95% CI 0.52-0.94 for those who had smoked for 21 years or more).
The possible protective effect of smoking might be due to its anti-oestrogenic effect [1,2,19]. Recently there has been renewed interest in the potential effect of smoking on breast cancer risk, and whether individuals may respond differently on the basis of differences in metabolism of bioproducts of smoking [20,21]. Different relationships between smoking and breast cancer risk have been suggested that are dependent on the rapid or slow status of acetylators of aromatic amines [20,21]. More recent studies [22,23], however, do not support these findings.
The present study design minimized the opportunity for bias to influence the findings. Because subjects were unaware of their own case-control status, the possibility of recall bias in reporting smoking status was minimized. Systematic error in the assessment of mammograms was avoided because reading was done without knowledge of the risk factor data. Furthermore, the associations observed are unlikely to be explained by the confounding effect of other known breast cancer risk factors, because we adjusted for these in the analysis. We did not have information on passive smoking status, however, which has recently been reported to be a possible confounder [5,6,21,24].
The present data indicate that adjustment for current smoking status is important when evaluating the relationship between mammographic parenchymal pattern and breast cancer risk. They also indicate smoking as a prominent potential confounder when analyzing effects of other risk factors such as obesity-related variables. It seems that parenchymal patterns may act as an informative biomarker of the effect of cigarette smoking on breast cancer risk.
PMCID: PMC13911  PMID: 11056684
mammography; screening; smoking; Wolfe's parenchymal patterns
14.  Smoking, Smoking Cessation and Risk of Symptomatic Peripheral Artery Disease in Women: A Prospective Study 
Annals of internal medicine  2011;154(11):719-726.
Background
The detrimental effects of smoking on risk of myocardial infarction and stroke are well documented, but less information is available regarding peripheral artery disease (PAD), particularly among women.
Objective
To prospectively assess the association of current smoking status, cumulative smoking exposure and smoking cessation with incident symptomatic PAD in women
Design
Prospective cohort study
Setting
U.S. female health care professionals in the Women's Health Study
Participants
39825 women free of cardiovascular disease were prospectively followed for a median of 12.7 years.
Measurements
Incident symptomatic PAD (n=178). Cox proportional hazards models were used to compare PAD risk among never (n=20336) and former smoking (n=14263) women, women who smoked <15 cigarettes/day (n=1967) and women who smoked ≥15 cigarettes/day (n=3259).
Results
Age-adjusted incidences across smoking categories were 0.12, 0.34, 0.95 and 1.63 per 1000 person-years of follow-up. Multivariable adjustment had little impact on this risk gradient; adjusted hazard ratios (HRs) (95% confidence intervals (CIs)) were 3.14 (2.01–4.90), 8.93 (5.02–15.89) and 16.95 (10.77–26.67) compared with never-smokers. Additional adjustment for high sensitivity C-reactive protein and soluble intercellular adhesion molecule 1 among women with available blood samples (n=28314, 117 events) attenuated risk estimates with HRs of 5.58 (2.61–11.93) and 9.52 (5.17–7.53) for women smoking <15 and ≥15 cigarettes/day, respectively. We found a strong dose-response relationship for lifetime exposure such that the fully adjusted HR’s for 0 (reference), <10, 10–30 and ≥30 pack years were 2.52 (1.49–4.25), 6.75 (4.33–10.52) and 11.09 (6.94–17.72). Compared to current smokers, the adjusted HRs (95% CIs) for smoking abstinence of <10 years, 10–20 years, >20 years and lifelong abstinence were 0.39 (0.24–0.66), 0.28 (0.17–0.46), 0.16 (0.10–0.26) and 0.08 (0.05–0.12).
Limitation
The use of symptomatic PAD as the primary a priori end point excludes asymptomatic disease.
Conclusion
Among initially healthy women, smoking is a potent risk factor for symptomatic PAD, an effect partially explained by subclinical inflammation. Smoking cessation substantially reduces PAD risk, but an increased occurrence of PAD persists even among former smokers who maintain abstinence.
Primary Funding Source
National Heart, Lung, and Blood Institute and National Cancer Institute
doi:10.1059/0003-4819-154-11-201106070-00003
PMCID: PMC3111942  PMID: 21646555
Peripheral artery disease; cardiovascular disease; smoking; inflammation; women
15.  Passive smoking and cardiorespiratory health in a general population in the west of Scotland. 
BMJ : British Medical Journal  1989;299(6696):423-427.
OBJECTIVE-To assess the risk of cardiorespiratory symptoms and mortality in non-smokers who were passively exposed to environmental smoke. DESIGN--Prospective study of cohort from general population first screened between 1972 and 1976 and followed up for an average of 11.5 years, with linkage of data from participants in the same household. SETTING--Renfrew and Paisely, adjacent burghs in urban west Scotland. SUBJECTS--15,399 Men and women (80% of all those aged 45-64 resident in Renfrew or Paisley) comprised the original cohort; 7997 attended for multiphasic screening with a cohabitee. Passive smoking and control groups were defined on the basis of a lifelong non-smoking index case and whether the cohabitee had ever smoked or never smoked. MAIN OUTCOME MEASURE--Cardiorespiratory signs and symptoms and mortality. RESULTS--Each of the cardiorespiratory symptoms examined produced relative risks greater than 1.0 (though none were significant) for passive smokers compared with controls. Adjusted forced expiratory volume in one second was significantly lower in passive smokers than controls. All cause mortality was higher in passive smokers than controls (rate ratio 1.27 (95% confidence interval 0.95 to 1.70)), as were all causes of death related to smoking (rate ratio 1.30 (0.91 to 1.85] and mortality from lung cancer (rate ratio 2.41 (0.45 to 12.83)) and ischaemic heart disease (rate ratio 2.01 (1.21 to 3.35)). When passive smokers were divided into high and low exposure groups on the basis of the amount smoked by their cohabitees those highly exposed had higher rates of symptoms and death. CONCLUSION--Exposure to environmental tobacco smoke cannot be regarded as a safe involuntary habit.
PMCID: PMC1837285  PMID: 2507000
16.  Lung Cancer Occurrence in Never-Smokers: An Analysis of 13 Cohorts and 22 Cancer Registry Studies  
PLoS Medicine  2008;5(9):e185.
Background
Better information on lung cancer occurrence in lifelong nonsmokers is needed to understand gender and racial disparities and to examine how factors other than active smoking influence risk in different time periods and geographic regions.
Methods and Findings
We pooled information on lung cancer incidence and/or death rates among self-reported never-smokers from 13 large cohort studies, representing over 630,000 and 1.8 million persons for incidence and mortality, respectively. We also abstracted population-based data for women from 22 cancer registries and ten countries in time periods and geographic regions where few women smoked. Our main findings were: (1) Men had higher death rates from lung cancer than women in all age and racial groups studied; (2) male and female incidence rates were similar when standardized across all ages 40+ y, albeit with some variation by age; (3) African Americans and Asians living in Korea and Japan (but not in the US) had higher death rates from lung cancer than individuals of European descent; (4) no temporal trends were seen when comparing incidence and death rates among US women age 40–69 y during the 1930s to contemporary populations where few women smoke, or in temporal comparisons of never-smokers in two large American Cancer Society cohorts from 1959 to 2004; and (5) lung cancer incidence rates were higher and more variable among women in East Asia than in other geographic areas with low female smoking.
Conclusions
These comprehensive analyses support claims that the death rate from lung cancer among never-smokers is higher in men than in women, and in African Americans and Asians residing in Asia than in individuals of European descent, but contradict assertions that risk is increasing or that women have a higher incidence rate than men. Further research is needed on the high and variable lung cancer rates among women in Pacific Rim countries.
Michael Thun and colleagues pooled and analyzed comprehensive data on lung cancer incidence and death rates among never-smokers to examine what factors other than active smoking affect lung cancer risk.
Editors' Summary
Background.
Every year, more than 1.4 million people die from lung cancer, a leading cause of cancer deaths worldwide. In the US alone, more than 161,000 people will die from lung cancer this year. Like all cancers, lung cancer occurs when cells begin to divide uncontrollably because of changes in their genes. The main trigger for these changes in lung cancer is exposure to the chemicals in cigarette smoke—either directly through smoking cigarettes or indirectly through exposure to secondhand smoke. Eighty-five to 90% of lung cancer deaths are caused by exposure to cigarette smoke and, on average, current smokers are 15 times more likely to die from lung cancer than lifelong nonsmokers (never smokers). Furthermore, a person's cumulative lifetime risk of developing lung cancer is related to how much they smoke, to how many years they are a smoker, and—if they give up smoking—to the age at which they stop smoking.
Why Was This Study Done?
Because lung cancer is so common, even the small fraction of lung cancer that occurs in lifelong nonsmokers represents a large number of people. For example, about 20,000 of this year's US lung cancer deaths will be in never-smokers. However, very little is known about how age, sex, or race affects the incidence (the annual number of new cases of diseases in a population) or death rates from lung cancer among never-smokers. A better understanding of the patterns of lung cancer incidence and death rates among never-smokers could provide useful information about the factors other than cigarette smoke that increase the likelihood of not only never-smokers, but also former smokers and current smokers developing lung cancer. In this study, therefore, the researchers pooled and analyzed a large amount of information about lung cancer incidence and death rates among never smokers to examine what factors other than active smoking affect lung cancer risk.
What Did the Researchers Do and Find?
The researchers analyzed information on lung cancer incidence and/or death rates among nearly 2.5 million self-reported never smokers (men and women) from 13 large studies investigating the health of people in North America, Europe, and Asia. They also analyzed similar information for women taken from cancer registries in ten countries at times when very few women were smokers (for example, the US in the late 1930s). The researchers' detailed statistical analyses reveal, for example, that lung cancer death rates in African Americans and in Asians living in Korea and Japan (but not among Asians living in the US) are higher than those in people of the European continental ancestry group. They also show that men have higher death rates from lung cancer than women irrespective of racial group, but that women aged 40–59 years have a slightly higher incidence of lung cancer than men of a similar age. This difference disappears at older ages. Finally, an analysis of lung cancer incidence and death rates at different times during the past 70 years shows no evidence of an increase in the lung cancer burden among never smokers over time.
What Do These Findings Mean?
Although some of the findings described above have been hinted at in previous, smaller studies, these and other findings provide a much more accurate picture of lung cancer incidence and death rates among never smokers. Most importantly the underlying data used in these analyses are now freely available and should provide an excellent resource for future studies of lung cancer in never smokers.
Additional Information.
Please access these Web sites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.0050185.
The US National Cancer Institute provides detailed information for patients and health professionals about all aspects of lung cancer and information on smoking and cancer (in English and Spanish)
Links to other US-based resources dealing with lung cancer are provided by MedlinePlus (in English and Spanish)
Cancer Research UK provides key facts about the link between lung cancer and smoking and information about all other aspects of lung cancer
doi:10.1371/journal.pmed.0050185
PMCID: PMC2531137  PMID: 18788891
17.  Association between Smoking, Passive Smoking, and Erectile Dysfunction: Results from the Boston Area Community Health (BACH) Survey 
European urology  2007;52(2):416-422.
Introduction
Although previous studies report an association between erectile dysfunction (ED) and smoking, few have examined the impact of passive smoke exposure on ED. This analysis examines the association of active and passive smoking and ED and investigates a dose-response effect of smoking.
Methods
The Boston Area Community Heath (BACH) survey is a study of urologic symptoms in a racially and ethnically diverse population. BACH used a multistage stratified random sample to recruit 2301 men, aged 30–79 yr, from the city of Boston. ED was assessed using the five-item International Index of Erectile Function. Smoking and passive smoking were assessed by self-report. Analyses adjusted for sociodemographic and lifestyle factors and important chronic illnesses.
Results
An association between smoking and ED was observed with a significant trend in increased risk of ED with cumulative pack-years of smoking (adjusted odds ratio [OR] = 1.68; 95% confidence interval [CI], 1.03, 2.30 for ≥ 20 pack-years). Compared to never smokers not exposed to passive smoking, men who never smoked but were exposed to passive smoking had a moderate, statistically nonsignificant, increase in risk of ED (adjusted OR = 1.33; 95%CI: 0.69, 2.55) comparable to the OR observed for a cumulative exposure of 10–19 pack-years of active smoking (adjusted OR = 1.25; 95%CI, 0.68, 2.30).
Conclusions
Results indicate a dose-response association between smoking and ED with a statistically significant effect observed with ≥ 20 pack-years of exposure. Passive smoking is associated with a small, statistically nonsignificant increase in risk of ED comparable to approximately 10–19 pack-years of active smoking.
doi:10.1016/j.eururo.2007.03.015
PMCID: PMC2139983  PMID: 17383811
Epidemiology; Erectile dysfunction; Passive smoking; Smoking
18.  Passive Smoking and Risk of Breast Cancer in the California Teachers Study*†‡ 
Background
Although recent reviews have suggested active smoking to be a risk factor for breast cancer, the association with passive smoke exposure remains controversial. This risk association was explored in a large prospective study of women, the California Teachers Study.
Methods
Detailed lifetime information on passive smoke exposure by setting (home, work, or social) and by age of exposure were collected in 1997 from 57,523 women who were lifetime nonsmokers and had no history of breast cancer. In the ensuing decade, a total of 1,754 women were diagnosed with invasive breast cancer. Cox proportional hazards models were fit to estimate hazard ratios (HRs) and 95% confidence intervals (95% CI) associated with several lifetime passive smoke exposure metrics.
Results
For all breast cancer, measures of higher lifetime passive smoking intensity and duration were associated with non-statistically significant HRs of 1.11 to 1.14. For postmenopausal women, HRs for lifetime low, medium and high cumulative exposure were 1.17 (95%CI 0.91, 1.49), 1.19 (95%CI 0.93, 1.53), and 1.26 (95% CI 0.99, 1.60). For women exposed in adulthood (age ≥20) risk was elevated at the highest level of cumulative exposure (HR=1.18, 95% CI 1.00, 1.40), primarily among postmenopausal women (HR=1.25, 95% CI 1.01, 1.56). A statistically significant dose response was detected when analysis was restricted to women with moderate to high levels of passive smoke exposure.
Conclusion
These results suggest that cumulative exposures to high levels of side stream smoke may increase breast cancer risk among postmenopausal women who themselves have never smoked tobacco products.
doi:10.1158/1055-9965.EPI-09-0936
PMCID: PMC2908531  PMID: 19959687
passive smoking; tobacco; breast cancer; cohort study; women
19.  Alcohol, smoking, passive smoking and caffeine in relation to breast cancer risk in young women. UK National Case-Control Study Group. 
British Journal of Cancer  1994;70(1):112-119.
The UK National Case-Control Study Group has examined the relationship between smoking (both own smoking and passive), alcohol consumption and caffeine consumption and the risk of breast cancer. A total of 755 women with breast cancer diagnosed before the age of 36, each with an age-matched general population control, were interviewed, and detailed information on reproductive, contraceptive and medical history, personal attributes and habits were obtained. Additional data on passive smoking were obtained from a subgroup of women. There was no evidence of a statistically significant difference in breast cancer risk between subjects who had ever smoked as much as one cigarette per day and those who had not [relative risk (RR) = 1.01, 95% confidence interval (CI) 0.81-1.26]. Most relative risks for passive smoking exceeded unity, but there was little evidence of significant trends with increasing exposure. The lack of effect of own smoking, and the fact that such smokers are also themselves exposed to the effects of passive smoking, makes any relationship between exposure to others' smoking and breast cancer risk implausible. Alcohol consumption during the year prior to diagnosis and at ages 18 and 25 was examined. Consumers of 0.1-4.9 and 5.0-14.9 g per day generally had non-significantly increased risks compared with never drinkers, but consumers of more than 15 g per day had reduced risks.
PMCID: PMC2033307  PMID: 8018520
20.  Household endotoxin levels and the risk of non-Hodgkin lymphoma 
Cancer causes & control : CCC  2013;24(2):357-364.
Objective
Endotoxin, a component of the outer membrane of gram-negative bacteria, elicits a strong innate and inflammatory immune response associated with secretion of pro-inflammatory cytokines, including tumor necrosis factor-alpha (TNF-α). Because TNF-α polymorphisms that increase TNF-α production are associated with an increased risk of non-Hodgkin lymphoma (NHL), we hypothesized that increased levels of household endotoxin would be associated with an increased NHL risk.
Methods
We evaluated this association in the National Cancer Institute/Surveillance, Epidemiology and End Result (NCI/SEER) NHL multi-center population-based case-control study. Used vacuum cleaner bags were collected from participants during a home interview. Dust samples from the bags of 594 cases and 442 controls were analyzed for endotoxin (Endotoxin Unit [EU]/mg of dust) using the kinetic chromogenic Limulus amebocyte lysate assay. Multivariable logistic regression was used to estimate the effect of endotoxin on NHL risk adjusted for age, sex, race, education, study center, and farm exposure.
Results
Endotoxin was not associated with NHL overall (odds ratio [OR] for highest quartile of endotoxin levels = 0.81, 95% confidence interval [CI]= 0.55,1.20; P for trend=0.35), or with diffuse large B-cell lymphoma (OR= 0.63, 95% CI= 0.34, 1.16; P= 0.31) or follicular lymphoma (OR= 0.1.07, 95% CI=0.61, 1.89; P=0.73) subtypes. Both working and living on a farm were associated with higher household endotoxin levels compared to never working (P=0.009) or living (P=0.01) on a farm. Excluding farmers from the analysis did not change the results.
Conclusions
We found no evidence of a role for household endotoxin in NHL etiology.
doi:10.1007/s10552-012-0121-9
PMCID: PMC3800025  PMID: 23277417
Endotoxin; Non-Hodgkin lymphoma; Epidemiology; Farming; Risk; Case-control
21.  Genetic variation in N-acetyltransferase 1 (NAT1) and 2 (NAT2) and risk of non-Hodgkin lymphoma 
Pharmacogenetics and genomics  2006;16(8):537-545.
Background
Animal studies suggest that lymphomagenesis can be induced by exposure to carcinogenic aromatic and heterocyclic amines found in diet, cigarette smoke, and the environment, but human epidemiologic investigations of these exogenous exposures have yielded conflicting results. As part of our evaluation of the role of aromatic and heterocyclic amines, which are metabolized by N-acetyltransferase (NAT) enzymes, in the etiology of non-Hodgkin lymphoma (NHL), we examined NHL risk in relation to genetic variation in NAT1 and NAT2 and exposure to cigarette smoke and dietary heterocyclic amines and mutagens.
Methods
We genotyped ten common single nucleotide polymorphisms (SNPs) in NAT1 and NAT2 among 1136 cases and 922 controls from a population-based case–control study in four geographic areas of the US. Relative risk of NHL for NAT1 and NAT2 genotypes, NAT2 acetylation phenotype, and exposure to cigarette smoke and dietary heterocyclic amines and mutagens was estimated using odds ratios (ORs) and 95% confidence intervals (CIs) derived from unconditional logistic regression models.
Results
We observed increased risk of NHL among individuals with the NAT1*10/*10 genotype compared with individuals with other NAT1 genotypes (OR=1.60, 95% CI 1.04–2.46, p=0.03). We also observed increased NHL risk in a dose-dependent model among NAT2 intermediate- and rapid-acetylators in comparison with slow-acetylators, although only the trend was statistically significant (intermediate: OR=1.18, 95% CI 0.97–1.44, p=0.1; rapid: OR=1.43, 95% CI 0.97–2.14, p=0.07; p for linear trend=0.03). Compared with nonsmokers, NHL risk estimates for current cigarette smoking were increased only among NAT2 intermediate/rapid-acetylators (OR=2.44, 95% CI 1.15–5.20, p=0.02).
Conclusions
Our data provide evidence that NAT1 and NAT2 genotypes are associated with NHL risk and support a contributory role for carcinogenic aromatic and/or heterocyclic amines in the multi-factorial etiology of NHL.
doi:10.1097/01.fpc.0000215071.59836.29
PMCID: PMC1986787  PMID: 16847422
lymphoma, non-Hodgkin; N-acetyltransferase 1; N-acetyltransferase 2; genetic variation; polymorphism, single nucleotide
22.  Active and passive cigarette smoking and the risk of endometrial cancer in Poland 
Background
Epidemiological studies have consistently reported that active cigarette smoking is inversely associated with endometrial cancer risk. However, dose-response relationships with quantitative measures of active smoking or passive smoking remain less clear.
Methods
Data on lifetime active and passive smoking were collected for 551 endometrial cancer cases and 1925 controls in a population-based case-control study conducted during 2001–2003 in Poland (Warsaw and Łódz).
Results
Compared with never active smokers, active current (Odds Ratio (OR)=0.51, 95% Confidence Interval (CI): 0.39, 0.68) and former smokers (OR=0.60, 95% CI: 0.45, 0.80) were at a statistically significantly decreased risk. We did not observe statistically significant inverse dose-response relationships with increasing exposure with duration and cumulative measures. However, there was some indication that the highest category of number of years (OR=0.35, 95% CI: 0.23–0.55), intensity (OR=0.41, 95% CI: 0.24–0.69), and dose (OR=0.38, 95% CI: 0.24–0.60) of smoking among current smokers had the greatest inverse association compared to never smokers. Our data did not support the presence of an inverse association with passive smoking among never active smokers (OR=0.92; 95% CI: 0.65, 1.29).
Conclusion
Our results support that long-term and heavy smoking among current smokers strongly influence endometrial cancer risk.
doi:10.1016/j.ejca.2009.11.015
PMCID: PMC2851155  PMID: 20036529
Endometrial cancer; Active smoking; Passive smoking
23.  Respiratory symptoms and lung function effects of domestic exposure to tobacco smoke and cooking by gas in non-smoking women in Singapore. 
STUDY OBJECTIVES--To investigate the effects of passive exposure to tobacco smoke and gas cooking at home on respiratory symptoms and lung function of non-smoking women. SETTING--Evidence on the effects of passive smoking and exposure to nitrogen dioxide from gas cooking on the respiratory health of adults is limited and variable. Over 97% of women in Singapore do not smoke, and a principal source of indoor air pollution for housewives is passive smoking and gas cooking. DESIGN--This was a cross sectional (prevalence) study of a population based sample of 2868 adults aged 20 to 74 years in Singapore. A structured questionnaire administered by trained interviewers was used to collect data on passive smoking, gas cooking, respiratory symptoms, and other relevant variables. Passive smoking was defined as exposure to cigarette smoke from one or more members of the household who had ever smoked. Gas cooking was defined in terms of the weekly frequency of gas cooking, as well as the frequency with which the respondent's kitchen was filled with heavy cooking fumes (rarely, occasionally, often). Forced expiratory volume in one second (FEV1) was measured by using a portable Micro-spirometer. Multivariate analyses were used to estimate relative odds of association for respiratory symptoms and FEV1 effect, with adjustment for potential confounding variables. PARTICIPANTS--Of a total of 1438 women in the sample, 1282 women who had never smoked provided questionnaire data and 1008 women provided acceptable readings of FEV1 for analysis. MAIN RESULTS--Passive smoking was significantly associated with greater relative odds of usual or chronic cough and phlegm, wheezing, and breathlessness on exertion, as well as lower FEV1. Greater relative odds of respiratory symptoms were also associated with the weekly frequency of gas cooking, although these results were statistically insignificant. Chronic cough and phlegm and breathlessness on exertion, however, were significantly associated with the frequency with which the kitchen was filled with heavy cooking fumes. A lower FEV1 was found in women who cooked frequently (more than thrice a week). CONCLUSION--Domestic exposure to cigarette smoke and gas cooking is associated with increased risks of respiratory symptoms and impairment of lung function in non-smoking women in Singapore.
PMCID: PMC1059858  PMID: 8120499
24.  Associations Between Anthropometry, Cigarette Smoking, Alcohol Consumption, and Non-Hodgkin Lymphoma in the Prostate, Lung, Colorectal, and Ovarian Cancer Screening Trial 
American Journal of Epidemiology  2010;171(12):1270-1281.
Prospective studies of lifestyle and non-Hodgkin lymphoma (NHL) are conflicting, and some are inconsistent with case-control studies. The Prostate, Lung, Colorectal, and Ovarian (PLCO) Cancer Screening Trial was used to evaluate risk of NHL and its subtypes in association with anthropometric factors, smoking, and alcohol consumption in a prospective cohort study. Lifestyle was assessed via questionnaire among 142,982 male and female participants aged 55–74 years enrolled in the PLCO Trial during 1993–2001. Hazard ratios and 95% confidence intervals were calculated using Cox proportional hazards regression. During 1,201,074 person-years of follow-up through 2006, 1,264 histologically confirmed NHL cases were identified. Higher body mass index (BMI; weight (kg)/height (m)2) at ages 20 and 50 years and at baseline was associated with increased NHL risk (Ptrend < 0.01 for all; e.g., for baseline BMI ≥30 vs. 18.5–24.9, hazard ratio = 1.32, 95% confidence interval: 1.13, 1.54). Smoking was not associated with NHL overall but was inversely associated with follicular lymphoma (ever smoking vs. never: hazard ratio = 0.62, 95% confidence interval: 0.45, 0.85). Alcohol consumption was unrelated to NHL (drinks/week: Ptrend = 0.187). These data support previous studies suggesting that BMI is positively associated with NHL, show an inverse association between smoking and follicular lymphoma (perhaps due to residual confounding), and do not support a causal association between alcohol and NHL.
doi:10.1093/aje/kwq085
PMCID: PMC2915494  PMID: 20494998
alcoholic beverages; anthropometry; body height; body mass index; body weight; life style; lymphoma; non-Hodgkin; smoking
25.  Parental and household smoking and the increased risk of bronchitis, bronchiolitis and other lower respiratory infections in infancy: systematic review and meta-analysis 
Respiratory Research  2011;12(1):5.
Background
Passive smoke exposure increases the risk of lower respiratory infection (LRI) in infants, but the extensive literature on this association has not been systematically reviewed for nearly ten years. The aim of this paper is to provide an updated systematic review and meta-analysis of studies of the association between passive smoking and LRI, and with diagnostic subcategories including bronchiolitis, in infants aged two years and under.
Methods
We searched MEDLINE and EMBASE (to November 2010), reference lists from publications and abstracts from major conference proceedings to identify all relevant publications. Random effect pooled odds ratios (OR) with 95% confidence intervals (CI) were estimated.
Results
We identified 60 studies suitable for inclusion in the meta-analysis. Smoking by either parent or other household members significantly increased the risk of LRI; odds ratios (OR) were 1.22 (95% CI 1.10 to 1.35) for paternal smoking, 1.62 (95% CI 1.38 to 1.89) if both parents smoked, and 1.54 (95% CI 1.40 to 1.69) for any household member smoking. Pre-natal maternal smoking (OR 1.24, 95% CI 1.11 to 1.38) had a weaker effect than post-natal smoking (OR 1.58, 95% CI 1.45 to 1.73). The strongest effect was on bronchiolitis, where the risk of any household smoking was increased by an OR of 2.51 (95% CI 1.96 to 3.21).
Conclusions
Passive smoking in the family home is a major influence on the risk of LRI in infants, and especially on bronchiolitis. Risk is particularly strong in relation to post-natal maternal smoking. Strategies to prevent passive smoke exposure in young children are an urgent public and child health priority.
doi:10.1186/1465-9921-12-5
PMCID: PMC3022703  PMID: 21219618

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