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Background: Debates over the importance of "lifestyle" versus "environment" contributions to cancer have been going on for over 40 years. While it is clear that cigarette smoking is the most significant cancer risk factor, the contributions of occupational and environmental carcinogens in air, water and food remain controversial. In practice, most cancer prevention messaging focuses on reducing cigarette smoking and changing other personal behaviors with little mention of environmental chemicals, despite widespread exposure to many known carcinogens. To inform decision-making on cancer prevention priorities, we evaluated the potential impact of smoking cessation on cancer rates., Methods: Using cancer incidence data from 612 counties in the SEER database, and county-level smoking prevalences, we investigated the impact of smoking cessation on incidence for 12 smoking-related cancer types, 2006-2016. A multilevel mixed-effects regression model quantified the association between county-level smoking prevalence and cancer incidence, adjusting for age, gender and variability over time and among counties. We simulated complete smoking cessation and estimated the effects on county-level cancer rates., Results: Regression models showed the expected strong association between smoking prevalence and cancer incidence. Simulating complete smoking cessation, the incidence of the 12 smoking-related cancer types fell by 39.8% (54.9% for airways cancers; 28.9% for non-airways cancers). And, while the actual rates of smoking-related cancers from 2006 to 2016 declined (annual percent change (APC) = - 0.8, 95% CI = - 1.0 to - 0.5%), under the scenario of smoking elimination, the trend in cancer incidence at these sites was not declining (APC = - 0.1, 95% CI = - 0.4 to + 0.1%). Not all counties were predicted to benefit equally from smoking elimination, and cancer rates would fall less than 10% in some counties., Conclusions: Smoking prevention has produced dramatic reductions in cancer in the US for 12 major types. However, we estimate that eliminating smoking completely would not affect about 60% of cancer cases of the 12 smoking-related types, leaving no improvement in the incidence trend from 2006 to 2016. We conclude that cancer prevention strategies should focus not only on lifestyle changes but also the likely contributions of the full range of risk factors, including environmental/occupational carcinogens.

Objective: To examine the association between intelligence quotient (IQ) measured at ages 18 to 20 and onset of smoking, and the association between IQ and smoking cessation., Methods: Data on IQ, smoking, mental health, and social background among 49,321 Swedish men born 1949 to 51, collected at conscription for military service in 1969, were used. The association between IQ and smoking cessation was investigated among those 694 members of the full cohort also interviewed in the Swedish Level of Living Conditions study 1981 to 2002., Results: Lower IQ measured at ages 18 to 20 was weakly associated with increased prevalence of smoking, independently of indicators of mental illness and social misbehavior measured in late adolescence. By contrast, smoking cessation later in life among those who smoked at ages 18 to 20 was not associated with IQ. Among smokers, lower IQ was significantly associated with a lower level of smoking after adjusting for other factors., Conclusion: Low IQ was associated with an increased prevalence of smoking in adolescence. However, the main part of this association disappeared after adjustment for measures of mental health and social function in early life. IQ was not associated with likelihood of quitting smoking.

Objectives: Several studies have reported an association between cigarette smoking and psychiatric illness. A common finding is that the prevalence of psychiatric illness among former smokers is much lower than among current smokers and is often similar to that among never-smokers. There are two alternative causal explanations for this association: either improved mental well-being results from smoking cessation; or those with poorer mental well-being are less successful at smoking cessation. The objective was to analyse a unique longitudinal data set to shed light on the direction of causality and to distinguish between these alternative explanations., Methods: Information on smoking status and indicators of poor mental well-being from childhood and adolescence was collected at age 18 in 1969 from 49 321 men at compulsory conscription for military service. Follow-up data on smoking status were collected among a random subset (n = 694) who participated in one or more annual national Swedish Surveys of Living Conditions in 1981-2001., Results: Approximately half of the smokers at age 18 in 1969 had quit by the time they were resurveyed (1981-2002). Those who had not quit and who reported smoking more than 10 cigarettes/day at age 18 (called persistent heavy smokers), were more likely to have had childhood and adolescent indicators of poor mental health measured at age 18 in 1969 than non-smokers or quitters., Conclusion: Our findings indicate that men who would subsequently be successful at smoking cessation reported better mental health and a lower prevalence of childhood mental health indicators at age 18 than persistent heavy smokers.

Background: Uncontrolled confounding by personal exposures like smoking can limit the inferential power of occupational cohort studies. We developed and demonstrate a refinement of an existing type of sensitivity analysis, indirect adjustment, for evaluating the potential magnitude of confounding by alcohol and tobacco. Results of a large retrospective cohort study of laryngeal cancer and exposure to metalworking fluids (MWF) are used to illustrate the methods., Methods: Data on smoking and drinking habits representative of the study cohort were obtained from a sample of US manufacturing workers from the 1977 National Health Interview Survey (NHIS). Two different mechanisms were assumed to affect the distribution of confounding factors between MWF exposure groups: socially determined and chance differences. Chance variation was investigated with Monte Carlo sampling from the NHIS survey distribution of smoking and drinking. An upper bound on systematic differences in smoking and drinking was set by assuming that differences between exposure groups within the same unionized blue collar workforce were very unlikely to be larger than differences between blue and white collar manufacturing workers in the NHIS data., Results: Under plausibly large differences in smoking and drinking habits among MWF exposure groups occurring by either mechanism, the exposure-risk association was unlikely to have been over- or under-estimated by as much as 20%., Conclusions: When comparing exposure groups within the same working population, it is unlikely that either systematic or chance differences in smoking and drinking habits will cause as much as a 20% change in the relative risk in large studies. While this study focused on an occupational exposure and laryngeal cancer, there are many situations in which epidemiologists are concerned that unmeasured 'lifestyle factors' may differ among exposure groups, and it would appear that the likely confounding effect of such differences will often be modest.

Objectives: Several studies have shown a relation between smoking and suicide. It is not clear if this relation should be considered causal, or if other risk factors for suicide, left unmeasured in many studies, might explain the smoking-suicide association. The aim of this cohort study was to analyse the role of smoking and other potential risk factors measured in adolescence on subsequent suicide., Methods: Information on smoking, and other potential risk factors from childhood and adolescence was collected among 49 323 men, born 1949-1951, at conscription for compulsory military training in the years 1969-1970. Mortality data were obtained from the Swedish cause of death register for the years 1971-1996., Results: There was a clear trend of increasing suicide risk with increasing intensity of smoking reported at conscription. Those smoking >20 cigarettes/day had a strongly increased relative risk of suicide (OR = 3.03, 95% CI: 1.72, 5.34) during the first 13 years of follow-up. From 14 to 26 years after conscription, the risk was only slightly weaker (OR = 2.53, 95% CI: 1.36, 4.72). When we adjusted for other risk factors for suicide measured at the conscription examination (psychiatric diagnosis, parental divorce, low emotional control, medication for nervous problems, contact with police and childcare, heavy alcohol consumption, drug use, and education) in a multivariate analysis, the trend with smoking intensity disappeared, and there was no longer an increased relative risk for the heavy smokers (follow-up years 1-13: OR = 0.98, 95% CI: 0.53, 1.82; years 14-26: OR = 1.31, 95% CI: 0.91, 1.87)., Conclusion: The increased risk of suicide among smokers was almost entirely explained by an increased prevalence of heavy alcohol consumption and low mental well-being among smokers. That is, the association between smoking and suicide is probably due to confounding by these other factors. These results do not support the hypothesis that tobacco consumption itself is a risk factor for suicide.

Objective: Meta-analysis was used to summarize the published evidence on the associations between alcohol and tobacco consumption and cancers of the oropharynx, pharynx, larynx, and esophagus. The objective was to produce summary risk estimates with uniform methods and on uniform exposure scales so that the magnitudes of the risks could be compared across tumor sites., Methods: Epidemiologic studies that estimated the effects of alcohol and tobacco consumption on the risk of cancers of the upper aero-digestive tract were identified from the MEDLINE database, 1966-2001. Alcohol and tobacco data were converted into common units (grams/week). For all studies meeting eligibility criteria, effect parameters (slopes) were estimated for both exposures. The exposure-risk slopes for each study were combined, site by site, using random effects meta-regression methods., Results: Fourteen studies met the final selection criteria. The carcinogenic effects of alcohol and tobacco were found to be multiplicative on the relative risk scale. Tobacco appeared to have a much stronger effect on the larynx than on any of the other aerodigestive sites, while alcohol's effect was strongest on the pharynx. The weakest association was that of alcohol and adenocarcinoma of the esophagus--an order of magnitude weaker than that for tobacco and laryngeal cancer., Conclusions: Meta-analysis was used to combine the results from all available studies, providing a comprehensive summary of the combined effects of alcohol and tobacco on the upper aerodigestive cancers.