1 Division of Occupational Health, Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden.
2 Department of Work Environment, University of Massachusetts Lowell, USA.
Correspondence: Tomas Hemmingsson, National Institute for Working Life,S-113 91 Stockholm, Sweden. E-mail: tomas.hemmingsson{at}niwl.se
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Abstract |
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Methods Information on smoking, and other potential risk factors from childhood and adolescence was collected among 49 323 men, born 19491951, at conscription for compulsory military training in the years 19691970. Mortality data were obtained from the Swedish cause of death register for the years 19711996.
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 113: OR = 0.98, 95% CI: 0.53, 1.82; years 1426: 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.
Accepted 4 April 2003
Suicide is a leading cause of death in early adulthood. Several studies have reported an association between tobacco smoking and suicide.15 There has been considerable debate in the literature about whether this association could be causal, or whether instead it is explained by confounding by other suicide risk factors.1,2,57 Several well-established risk factors suchas depression, alcohol consumption, and social isolation have frequently been shown to be more common among smokers.8 Recent studies have reported strong, dose-related associations between smoking and suicide, even after controlling for race, education, alcohol consumption, and marital status.25 To date no study has, as far as we know, adjusted for differences in mental health between groups of smokers and non-smokers despite the strong relation between mental health status and suicide.810
A unique longitudinal cohort study of 49 323 Swedish men provided an excellent opportunity to investigate the smokingsuicide association and in particular to explore the potential role of psychological factors in this association. The aim of this study was to investigate the relation between smoking and suicide and to what extent this relation could be explained by other individual risk factors, such as heavy alcohol consumption and drug use, as well as indicators of poor mental well-being. Two questions were addressed: (1) Was smoking at age 1820 related to suicide mortality during 26 years of follow-up? (2) To what extent could this relation be attributed to increased prevalence of indicators of poor mental well-being and alcohol use among smokers?
We have used data on smoking and other individual characteristics collected at compulsory conscription for military training among a cohort of young Swedish men in the years 1969and 1970, and data on their suicide mortality in the years 19711996. We have also used information on alcoholism diagnoses resulting in in-patient care during the follow-up period.
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Methods |
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Smoking and other potential risk factors for suicide mortality
At conscription, all men were asked to complete two questionnaires. The first concerned social background, behaviour and social adjustment, psychological factors, and general health. The second dealt specifically with substance use, e.g. tobacco smoking, drug, and alcohol consumption. All the conscripts were seen by a psychologist for a structured interview and assessment of intellectual capacity, social maturity, emotional control, and a few other predetermined scales. The ratings of the psychologists were regularly checked for inter-rater reliability. All conscripts were seen by a physician who diagnosed any disorders according to the Swedish version of the International Classification of Diseases Eighth Revision (ICD-8). Conscripts reporting or presenting psychiatric symptoms were seen by a psychiatrist and any diagnoses were also recorded according to ICD-8.
Besides smoking, other measures from the conscription examination were selected for inclusion in this analysis if they fell into one of three categories: known suicide risk factors in this material,9,11,12 a measure of social class (years of education at time of the conscription examination), and a diagnosis of alcoholism during the follow-up period from 1973 to 1996.
Information on cigarette smoking was collected through a questionnaire and all men were classified into one of five levels (non-smokers, 15 cigarettes/day, 510 cigarettes/day, 1120 cigarettes/day, >20 cigarettes/day). To simplify data presentation and facilitate comparisons to earlier studies on this topic, the lowest two smoking groups were combined into a 110 cigarettes/day group. Alcohol consumption (g 100% alcohol/week) was calculated on the basis of the answers to the questions on frequency and average consumed volume of beer, wine, and strong spirits. A composite variable, risky use of alcohol, was constructed from affirmative answers to one or more of the following: consumption 250 g 100% alcohol/ week, reporting the drinking of an eye-opener during a hangover, having been apprehended for drunkenness, or having often been drunk (the choices were: often, rather often, sometimes, and never).
The variable emotional control was assessed by a psychologist at conscription in five levels. Low emotional control, defined as a score of 1 or 2, was reported for 20% of the cohort, and served as a summary assessment of mental stability, emotional maturity, and tolerance for stress and frustration. Information on parental divorce, collected at conscription, was used as an indicator of conflicts among family members.13 The variable contact with police and child welfare authorities (at least once) indicated problem behaviour and has been shown to be strongly related to later psychiatric diagnosis.9 The conscripts were asked if they at least sometimes had been on medication for nervous problems, and an affirmative answer was used as another measure of psychological difficulties.
Follow-up data on suicide mortality
The cohort was linked to the National Cause of Death Register 19711996 held at the National Board of Health and Welfare using national personal identification numbers. For the years 19711986, cause of death was classified according to ICD-8, while for 19871996, the Ninth Revision was used. Suicide mortality classification did not differ between the two versions, and we used the following codes: 95.095.9 and 98.098.9.
Data on alcoholism diagnosis during follow-up
Record linkage with the psychiatric inpatient care register 19731996 from the National Board of Health and Welfare was also performed to identify diagnoses of alcoholism. In this register, all hospital episodes with psychiatric diagnoses were recorded for patients treated in any hospital (mental as well as general) in Sweden. Diagnoses were recorded at discharge of the patient. In this study we counted as alcoholic anyone with a primary or secondary diagnosis of alcoholism (alcohol psychosis [ICD-8: 291], alcoholism [ICD-8: 303], and alcohol intoxication [ICD-8: 980]) during the years 19731996.
Data analysis
The association between smoking and suicide for the years 19711996 was evaluated in both univariate and multivariate models using logistic regression models. Odds ratios were calculated as approximations of relative risks (RR). In the multivariate models, the RR associated with smoking was estimated controlling for the effects of risk factors measured at conscription in 1969 and 1970, as well as for alcoholism diagnosis during follow-up. Models were fit to the full data set, as well as separately for the periods 19711983 and 19841996 (only the results for the two separate periods are shown here). This division was made to examine possible differences in risk factors as the cohort aged, and because smoking information was only available at conscription and the probability of changes in smoking habits likely increased with time. Consequently, there was probably less misclassification of smoking status in the first versus the second period.
The RR presented are calculated for those 42 575 conscripts who contributed full information concerning all the variables included in the multivariate model in Table 2.
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Results |
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Smoking and suicide
The RR of suicide increased steadily with increasing amount of smoking (Table 3). The trend appeared somewhat stronger for the first 13 years after conscription than for the later period, primarily due to the especially high RR for the heaviest smokers in the first period. Inclusion of the eight risk factors (Table 2
) measured at conscription in the logistic regression model essentially eliminated the association between smoking and suicide (Table 3
). This effect was particularly marked for the early period (19711983) for which the P-value for trend went from 0.02 in the crude model to 0.76 after controlling for the other risk factors. For the later period, some increased risk of suicide among smokers still remained after controlling for the eight risk factors, although there was no longer any evidence of a trend in risk with increasing smoking. The model for the later period was additionally controlled for alcoholism diagnosis during follow-up (Table 3
). This further weakened the evidence of an association between smoking and suicide.
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Discussion |
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This study on smoking and suicide has several advantages compared with previous studies on the subject. The study population is representative of all young Swedish men during the period. The study includes data on important personal characteristics that have been previously shown to be suicide risk factors. The prospective nature of the study enhances the validity of these findings, because both smoking status and the other risk factors were assessed years before suicide occurred.
When comparing the early and later periods of follow-up, two differences could be observed. First, the crude smoking suicide association was weaker in the later period, either due to changes in suicide risk and its determinants as the cohort entered middle age, or because of the increasing misclassification of smoking status based on habits reported in the late teen years. Second, the eight risk factors, also measured at conscription, did not as fully explain the smokingsuicide association as they did for the first period. It is difficult to say why there may have been some residual smoking-related suicide risk, but the absence of a clear trend in risk with increasing smoking in the second period of follow-up argues against a direct causeeffect relation.
The number of suicides in this study is in accordance with expected numbers based on Swedish causes of death statistics in 1975 and 1980.14,15
Smoking and other risk factors measured at conscription
Information on smoking was collected at age 1820 and, like all questionnaire data, is likely to be misclassified to some degree. It is unlikely that this misclassification is related to suicide risk and so one might expect to observe a dilution of the smoking suicide relation. A more serious concern though, is that we had information on smoking status at only one point in time, while we know that habits change, particularly from the teenage years to middle age. Furthermore, smoking rates in Sweden declined dramatically over the relevant time period, much as they did in other western countries. In addition, there is evidence that those who stopped smoking during this period were different in potentially relevant aspects of their personalities and life circumstances compared with those who continued to smoke.16 In general, former smokers, like non-smokers, are reported to show lower rates of low mental well-being than current smokers.11 It is therefore likely that those at higher risk of suicide because of lower emotional control and other mental health problems in this study also were less likely to quit smoking. It might also be that those who persist in smoking (because of psychological problems) as a group are those most vulnerable to additional risk factors over the life course (such as divorce, unemployment, etc.). When suicide risk in the second period was adjusted for both the set of risk factors measured at conscription as well as for alcoholism diagnosis during follow-up (Table 3, Multivariate model 2), very little evidence of elevated suicide risk among smokers remained. This suggests that with more information on individual risk factors during the follow-up period, the slight residual smoking risk might be reduced even further.
There has been a lively debate in the literature over smoking and suicide. Strong opinions have been stated on the question of causality, with some holding that the association probably is causal5 and others that it is not.1,6 Miller and colleagues have taken a more cautious approach.2,3 One proposed causal mechanism has ascribed the smokingsuicide association to smoking-induced cancer or other chronic physical illnesses in turn leading to depression, despair, and ultimately suicide.2,17
The findings in our study argue against the smoking chronic physical illness
suicide pathway in at least two ways. First, little evidence for a smokingsuicide association remains after accounting for early life suicide risk factors. Second, the subjects in this study were too young to develop a significant burden of smoking-related chronic disease, particularly in the first period, when they were 1934 years old.
If low mental well-being were on the causal pathway between smoking and suicide, then it would be inappropriate to control for it. We think this is an unlikely explanation, however. First of all, several factors occurred in childhood (contact with police and child welfare, parental divorce, and attaining less than 10 years of education) and very likely preceded onset of smoking. Second, it seems implausible that much of the clinically diagnosed mental illness (or mental illness severe enough to require medication) at age 18 was a result of smoking. The far more likely explanation is that the apparent association between smoking and suicide is a consequence of: (1) an independent association between mental illness and suicide, and (2) a tendency for people with low emotional control and other mental health problems to start smoking and, once started, to have difficulty stopping.
Smoking is not only an effective toxic chemical delivery system, it is a behaviour with very complex social motivations and meanings. It is a marker for a wide range of other behaviours, lifestyle choices, certain educational and class backgrounds, beliefs and attitudes, and personality types. Additionally, the nicotine in cigarettes produces addiction, which means that smoking status is a relatively stable personal characteristic. Despite the well-known difficulties of obtaining an accurate smoking history, the simple smoker yes/no categorization is associated with a complex of other characteristics, dividing members of seemingly homogeneous populations into two groups which may well differ in many other ways besides the direct toxic exposures from the tobacco smoke (Table 2). Previous studies have attempted to control for personal characteristics which might represent suicide risk factors (for example by including marital status in smokingsuicide models), but the Swedish conscripts cohort is the only one that we know of in which detailed measures of mental well-being are available.
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Conclusion |
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Acknowledgments |
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References |
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2 Miller M, Hemenway D, Bell NS, Yore MM, Amoroso PJ. Cigarette smoking and suicide: a prospective study of 300 000 male active-duty Army soldiers. Am J Epidemiol 2000;151:106063.[Abstract]
3 Miller M, Hemenway D, Rimm E. Cigarettes and suicide: a prospective study of 50 000 men. Am J Public Health 2000;90:76873.
4 Tanskanen A, Tuomiletho J, Viinamaki H, Vartiainen E, Lethonen J, Puska P. Smoking and the risk of suicide. Acta Psychiatr Scand 2000; 101:24345.[CrossRef][ISI][Medline]
5 Leistikow BN, Martin DC, Samuels SJ. Injury death excesses in smokers: a 199095 United States national cohort study. Inj Prev 2000;6:27780.
6 Davey Smith G, Phillips AN, Neaton JD. Re: Cigarette smoking and suicide: a prospective study of 300 000 male active-duty army soldiers (letter). Am J Epidemiol 2001;153:307.
7 Miller M, Bell N, Yore M. Re: Cigarette smoking and suicide: a prospective study of 300 000 male active-duty army soldiers. The authors reply (letter). Am J Epidemiol 2001;153:308.[ISI]
8 Degenhardt L, Hall W. The relationship between tobacco use, substance-use disorders and mental health: results from the National Survey of Mental Health and Well-being. Nicotine Tob Res 2001;3:22534.[Medline]
9 Allebeck P, Allgulander C. Psychiatric diagnoses and predictors of suicide. Br J Psychiatry 1990;157:33944.[Abstract]
10 Appelby L, Shaw J, Amos T et al. Suicide within 12 months of contact with mental health services: national clinical survey. BMJ 1999;318: 123539.
11 Allebeck P, Allgulander C, Fischer L. Predictors of completed suicide in a cohort of 50 465 young men: the role of personality and deviant behaviour. BMJ 1988;297:17678.[ISI][Medline]
12 Larsson D, Hemmingsson T, Allebeck P, Lundberg I. Self-rated health and mortality among young men: what is the relation and how may it be explained? Scand J Public Health 2002;30:25966.[CrossRef][ISI][Medline]
13 Hawkins JD, Catalano RF, Miller JY. Risk and protective factors for alcohol and other drug problems in adolescence and early adulthood: Implications for substance abuse prevention. Psychol Bull 1992;112: 64105.[CrossRef][ISI][Medline]
14 SCB. Official Statistics of Sweden: Causes of Death 1975. Stockholm: National Bureau of Statistics, 1977.
15 SCB. Official Statistics of Sweden: Causes of Death 1980. Stockholm: National Bureau of Statistics, 1982.
16 Lundberg O, Rosen B, Rosen M. Who stopped smoking? Results from a panel survey of living conditions in Sweden. Soc Sci Med 1991; 32:61922.[CrossRef][ISI][Medline]
17 Louhivuori KA, Hakama M. Risk of suicide among cancer patients. Am J Epidemiol 1979;109:5965.[Abstract]