3.0 Introduction

Smoking of tobacco as we know it today, in the form of manufactured or 'factory-made' cigarettes, became common in Australia in the late 1800s. Pipe and cigar smoking was already widespread among men, but the convenience and ready availability of the cigarette soon made it a popular alternative. ¹ Manufactured cigarettes were supplied to Australians and their allies in the trenches of World War I, ¹ and by the end of World War II, nearly three quarters of Australian men and one quarter of women were smokers, the majority using cigarettes (see also Chapter 1, Section 1.1 ).

Similar changes in smoking behaviour had occurred in Western Europe and North America, and with them, a marked escalation in lung cancer death rates and the growing suspicion that cigarette use was implicated in this trend. By 1950 findings from two very important studies had been published in the medical literature and it was concluded that cigarette smoking and lung cancer appeared to be causally linked. ^{2, 3} The seminal UK doctors study initiated by Doll and Hill which has published findings in 1950, 1954, 1964, 1976, 1994 and 2004 has estimated that smoking kills about half of all persistent users, half of whom die in middle age. ^4-8

Several series of authoritative, landmark reports have since been published by national and international agencies, ⁱ documenting the health risks of smoking and calling for action to help halt the smoking epidemic. Of these, the most regular series has been that issued by the Office of the US Surgeon General. Since 1964, 31 comprehensive and rigorous reports on various aspects of tobacco and health have been issued by the US Surgeon General, repeating the conclusion that “smoking remains the leading preventable cause of premature disease and death in the United States,” and never finding reason to reverse any earlier conclusions of causality. ⁹ In fact, each report has expanded the list of diseases and other adverse health effects caused by smoking.

The 2004 report of the US Surgeon General, The Health Consequences of Smoking, published the following four major conclusions: ¹⁰

1. Smoking harms nearly every organ of the body, causing many diseases and reducing the health of smokers in general.
2. Quitting smoking has immediate as well as long-term benefits, reducing risks for diseases caused by smoking and improving health in general.
3. Smoking cigarettes with lower machine-measured yields of tar and nicotine provides no clear benefit to health.
4. The list of diseases caused by smoking has been expanded to include abdominal aortic aneurysm, acute myeloid leukaemia, cataract, cervical cancer, kidney cancer, pancreatic cancer, pneumonia, periodontitis and stomach cancer.

In addition, the 2014 report of the US Surgeon General, The Health Consequences of Smoking – 50 Years of Progress, published these major conclusions in regard to the health effects of smoking: ⁹

1. The century-long epidemic of cigarette smoking has caused an enormous avoidable public health tragedy. Since the first Surgeon General’s report in 1964 more than 20 million premature deaths [in the U.S] can be attributed to cigarette smoking.
2. The tobacco epidemic was initiated and has been sustained by the aggressive strategies of the tobacco industry, which has deliberately misled the public on the risks of smoking cigarettes.
3. Even 50 years after the first Surgeon General’s report, research continues to newly identify diseases caused by smoking, including such common diseases as diabetes mellitus, rheumatoid arthritis, and colorectal cancer.
4. In addition to causing multiple diseases, cigarette smoking has many other adverse effects on the body, such as causing inflammation and impairing immune function.
5. The burden of death and disease from tobacco use in the United States is overwhelmingly caused by cigarettes and other combusted tobacco products; rapid elimination of their use will dramatically reduce this burden.

Figure 3.0.1 shows each of the conditions causally linked to smoking as identified in the Surgeon General’s reports. Those in red indicate newly identified conditions in the latest report.

3.0.1 Defining causality

The US Surgeon General’s reports have provided a detailed review of definitions of causality of disease, and how measures of causality may be applied. Causality is determined by evaluating the available evidence and considering it against well-established criteria. The more that an observed association fulfils the criteria, the more likely it is that a causal relationship can be inferred. These criteria are outlined in the US Surgeon General’s Report for 2004: ¹⁰

Consistency: This refers to the persistence of the finding of an association between exposure and outcome in a number of methodologically valid studies undertaken in a range of settings. This helps ensure that possible confounding effects are eliminated, and also increases the statistical validity of the finding through the accumulation of additional evidence.

Strength of association: Strength refers both to magnitude of the association, and to its statistical strength. The greater the measured association and the more sound its statistical basis, the less likely it is that the findings are influenced by chance, bias, or unmeasured or poorly controlled confounding factors. However the observed association must also have a plausible basis in understood biological processes.

Specificity: Specificity refers to the degree to which exposure to the suspected disease causing agent can predict outcome. Other biological and epidemiological factors may need to be taken into account. For example, not all smokers develop lung cancer, and not all cases of lung cancer are caused by smoking. However, the extremely high relative risk for lung cancer in smokers, and the high percentage of lung cancers attributable to smoking, gives the association between smoking and lung cancer “a high degree of specificity”.

Temporality: Exposure to the causative factor must precede the onset of the disease. Considered alone, temporality is a poor predictor of causality, but no association can be considered to fulfil the criteria for causality if temporality is not satisfied.

Coherence, Plausibility and Analogy: Taken together, these three criteria require that the proposed causal relationship must not defy known scientific principles, and that it must be biologically plausible and consistent with experimentally demonstrated biological mechanisms and other relevant patterns.

Biologic Gradient (Dose-Response): This criterion refers to the observation of increased effect (for example incidence of disease) in response to increased dose (heavier and/or longer duration of smoking). Meeting this criterion forms a strong support for causality, except in the unlikely event that there is an unidentified confounder, which happens to be varying in the same manner as the observed dose and which could account for the measured association. Virtually all health outcomes causally linked to smoking have demonstrated a dose-response relationship of some description.

Experiment: This criterion refers to naturally occurring “experiments” that might be considered to imitate the conditions of a properly conducted experiment in a scientific environment, and whose outcomes might have the force of a true experiment. An example of a ‘natural experiment’ in the smoking arena is assessing the health consequences of quitting smoking. To attribute observed improvements in health outcomes to factors other than smoking cessation would necessitate identifying alternative influences and demonstrating that those who continued smoking had also attained a health benefit where that alternative influence was present .

The more closely an association fulfils the above criteria, the stronger its claim to causality. Not all inferences of causality will necessarily satisfy all criteria. For example where biological mechanisms may not be completely understood, causality may still be justified by satisfaction of other criteria, such as consistency and strength of association. Those applying the criteria must weigh the all of the scientific evidence and make a multidisciplinary judgement. ¹⁰

3.0.2 Tobacco—a leading preventable cause of death and disease globally

Tobacco use is responsible for a global pandemic of death and disease, causing one in 10 deaths worldwide.  In 2017, more than eight million deaths were attributable to tobacco use. More than seven million of those deaths were caused by direct tobacco use, while more than one million were caused by exposure to second-hand smoke ¹¹ (see Section 3.36). Researchers have estimated that on the basis of current rates of smoking initiation and cessation, smoking—which killed about 100 million people in the 20th century—will kill about one billion in the 21st century. ¹² Tobacco smoke contains more than 7,000 chemicals, including at least 69 known carcinogens. Harms from tobacco begin before birth, with smoking contributing to multiple adverse outcomes such as ectopic pregnancy, preterm delivery and stillbirth. Adding to the already long list, the most recent Surgeon General’s report concluded that smoking causes more diseases than previously thought, including two additional types of cancer. ⁹ A lifelong smoker loses on average a decade of life. ^{12, 13} In addition, exposure to secondhand smoke causes cancer, respiratory, and cardiovascular diseases, as well as adverse effects on the health of infants and children. ⁹

3.0.3 Tobacco—a leading preventable cause of death and disease in Australia

Smoking is the leading preventable cause of death and disease in Australia, responsible for more than 20,000 deaths in 2015, or more than one in every seven deaths (13.3%). ¹⁴ In 2015, 9.3% of the disease burden in Australia was due to tobacco use, making it the leading risk factor that contributed to disease burden and deaths. This equated to 443,235 years of healthy life lost (‘disability-adjusted life years’, or DALYs) from death and illness due to tobacco use in Australia in 2015. ¹⁴ Table 3.0.1 shows the number of deaths attributable to the top 10 leading risk factors in Australia in 2015, as well as their proportion of death and disease burden. Tobacco was responsible for more than three times as many deaths as the next most common drug, alcohol.

References

1. Walker R. Under fire. A history of tobacco smoking in Australia Melbourne: Melbourne University Press, 1984.

2. Doll R and Hill A. Smoking and carcinoma of the lung. British Medical Journal, 1950; 2:739-48. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2038856/?tool=pubmed

3. Wynder E and Graham E. Tobacco smoking as a possible etiologic factor in bronchogenic carcinoma. Journal of the American Medical Association, 1950; 143:329-36. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2623809/pdf/15744408.pdf

4. Doll R, Peto R, Boreham J, and Sutherland I. Mortality in relation to smoking: 50 years' observations on male British doctors. British Medical Journal, 2004; 328:1519–27. Available from: https://www.bmj.com/content/328/7455/1519

5. Doll R and Hill AB. Mortality in relation to smoking: Ten years' observations of British doctors. British Medical Journal, 1964; 1(5395):1399-410. Available from: https://www.ncbi.nlm.nih.gov/pubmed/14135164

6. Doll R and Peto R. Mortality in relation to smoking: 20 years' observations on male British doctors. British Medical Journal, 1976; 2(6051):1525-36. Available from: http://www.ncbi.nlm.nih.gov/pubmed/1009386

7. Doll R and Hill AB. The mortality of doctors in relation to their smoking habits: A preliminary report. British Medical Journal, 1954; 1(4877):1451–5. Available from: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2085438/

8. Doll R, Peto R, Wheatly L, Gray R, and Sutherland I. Mortality in relation to smoking: 40 years' observations on male British doctors. British Medical Journal, 1994; 309(6959):901–11. Available from: http://www.bmj.com/cgi/content/full/309/6959/901

9. US Department of Health and Human Services. The health consequences of smoking - 50 years of progress. Atlanta, GA: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2014. Available from: http://www.surgeongeneral.gov/library/reports/50-years-of-progress/.

10. US Department of Health and Human Services. The health consequences of smoking: A report of the Surgeon General. Atlanta, Georgia: US Department of Health and Human Services, Public Health Service, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2004. Available from: http://www.cdc.gov/tobacco/data_statistics/sgr/index.htm.

11. Global Health Data Exchange. Global burden of disease results. Institute for Health Metrics and Evaluation, University of Washington, 2018. Available from: http://ghdx.healthdata.org/gbd-results-tool.

12. Jha P, Ramasundarahettige C, Landsman V, Rostron B, Thun M, et al. 21st-century hazards of smoking and benefits of cessation in the United States. 2013; 368(4):341-50. Available from: https://www.nejm.org/doi/full/10.1056/NEJMsa1211128

13. Banks E, Joshy G, Weber MF, Liu B, Grenfell R, et al. Tobacco smoking and all-cause mortality in a large Australian cohort study: Findings from a mature epidemic with current low smoking prevalence. BMC Medicine, 2015; 13(1):38. Available from: http://www.biomedcentral.com/1741-7015/13/38

14. Australian Institute of Health and Welfare. Australian burden of disease study: Impact and causes of illness and death in Australia 2015. Australian Burden of Disease, Canberra: AIHW, 2019. Available from: https://www.aihw.gov.au/reports/burden-of-disease/burden-disease-study-illness-death-2015/contents/summary.

15. Peto R, Lopez AD, Pan H, Boreham J, and Thun M. Mortality from smoking in developed countries 1950 - 2020. 2015. Available from: http://gas.ctsu.ox.ac.uk/tobacco/contents.htm