... Methods. Tomas Hemmingsson 1,2, David Kriebel 3, Per Tynelius 4, Finn Rasmussen 4, Ingvar Lundberg 1,2. Study population

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1 European Journal of Public Health, Vol. 18, No. 1, ß The Author Published by Oxford University Press on behalf of the European Public Health Association. All rights reserved. doi: /eurpub/ckm079 Advance Access published on July 13, Adolescent mental health predicts quitting smoking in adulthood: a longitudinal analysis Tomas Hemmingsson 1,2, David Kriebel 3, Per Tynelius 4, Finn Rasmussen 4, Ingvar Lundberg 1,2 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 men at compulsory conscription for military service. Follow-up data on smoking status were collected among a random subset (n ¼ 694) who participated in one or more annual national Swedish Surveys of Living Conditions in Results: Approximately half of the smokers at age 18 in 1969 had quit by the time they were resurveyed ( ). 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. Keywords: adolescent mental health, smoking, smoking cessation, social function... everal well-established risk factors for later health outcomes Ssuch as depression, alcohol consumption and social isolation have frequently been shown to be more common among smokers. 1,2 Smoking rates in Sweden declined dramatically from the 1970s and onwards, much as they did in other western countries, 3 and there is evidence that those who stopped smoking during this period were different from those who continued to smoke with regard to some personality features and life circumstances. 4 In previous studies, smoking cessation has been related to socio-economic background, 5 adult social class, 4,6 daily amount and years spent smoking, 4,7 housing conditions 8 and age 7,8 It has also been reported that smoking cessation is associated with mental wellbeing. 9 An association between cigarette smoking and psychiatric illness has been frequently reported. It is a common finding that the prevalence of psychiatric illness and rate of suicide is much lower among former smokers than among current smokers. In addition, the occurrence of psychiatric illness among former smokers is often similar to that among never-smokers. 2 The literature is fairly consistent in finding that former smokers, like non-smokers, report better mental well-being than current smokers, but there is not yet strong evidence making it possible to distinguish between two alternative 1 Division of Occupational Health, Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden 2 National Institute for Working Life, Stockholm, Sweden 3 School of Health and Environment, University of Massachusetts Lowell, USA 4 Child and Adolescent Public Health Epidemiology Group, Department of Public Health Sciences, Karolinska Institute, Stockholm, Sweden Correspondence: Tomas Hemmingsson, PhD, Department of Public Health Sciences, Norrbacka pl.5, S Stockholm, tel: þ , fax: þ , tomas.hemmingsson@ki.se causal explanations for this association 2 : either (i) Those with high mental well-being are more successful at smoking cessation, or (ii) Improved mental well-being results from smoking cessation. We have previously shown that the prevalence of smoking at age was strongly related to several measures of low mental well-being, substance abuse and early childhood stressors in a cohort of about Swedish men interviewed at the time of military conscription in When these men were followed up over 25 years, the incidence of suicide was found to be strongly related to smoking at age We found, however, that this association disappeared after controlling for low mental well-being and substance abuse at age 18 20, and for markers of childhood emotional and psychological stresses. One limitation of this study was that smoking was only known at age 18 20, while the cohort was followed for suicide for about 25 more years, during which some of the smokers certainly quitted smoking. We were interested, therefore, in investigating the association between indicators of mental health in late adolescence and smoking cessation in this cohort. For the present investigation, we have used data on smoking and quitting behaviours during the years for the subset of 694 members of the original Swedish 1969 conscription cohort who also participated in the Swedish Surveys of Living Conditions. We have investigated how smoking cessation in adulthood was associated with indicators of poor mental health measured in late adolescence. Our objective was to provide evidence that might help to distinguish which of the earlier mentioned causal explanations is more likely to underlie the association between mental health and smoking cessation. Methods Study population The study was based on data from a nation-wide survey of young Swedish males aged 18 20, who were conscripted

2 Smoking and mental health 67 Study populations: All male conscripts N = 49,321 Random sub-cohort w/ at least 1 survey n = 694 AGE: YEAR: Data: Conscription Survey Annual Surveys * smoking yes/no * smoking yes/no * cigarettes/day * psych. medications * psych. diagnoses Figure 1 Timeline showing cohort and sub-cohort definitions, and timing of surveys. The cohort consisted of all Swedish males presenting for mandatory conscription at age 18 in 1969 (see text for details). The sub-cohort was the 694 randomly selected members of the full cohort who were surveyed in at least one annual Survey of Living Conditions conducted annually between 1981 and 2002 for compulsory military service in 1969 and The background of the Swedish conscription surveys and the variables included have been presented in detail elsewhere. 15,16 Only 2 3% of all Swedish men belonging to this cohort were exempted from conscription; in most cases due to severe handicaps or congenital disorders. Ninety-eight percent of all men conscripted in 1969 and 1970 were born in ; the remaining 2% were born before For simplicity, we will refer to this cohort as being age 18 at conscription in 1969, while in fact, the cohort s ages ranged from 18 to 20, and they were conscripted in 1969 and Six hundred and ninety-four members of this cohort were randomly selected for participation (and subsequently interviewed) in at least one of the Swedish Surveys of Living Conditions, conducted annually by Statistics Sweden, between 1981 and This subset (linked by Sweden s system of unique individual identifiers) makes up the study population in the present investigation. The Surveys of Living Conditions have been conducted annually since 1981, using national stratified random samples of the population ages Samples varying from 7000 to persons were interviewed every year, each in a 1 h private session, and the response rates have been around 80% or more. As part of the Swedish Surveys of Living Conditions, a subset of the sample is re-interviewed after 6 years, and from 1986, about a third of those interviewed were re-interviews from the sample of 6 years prior, while the remaining twothirds of the sample were new interviews. The probability of any given individual being included in the survey for the first time was about 10 per for the years and about 6 per for the following years. Based on those probabilities, we would expect the chance intersection of the 1969 conscription cohort with the Surveys of Living Conditions to include about 700 persons; agreeing very well with the 694 study subjects actually found. Information on smoking and other variables at the conscription survey in 1969 At conscription, all men were asked to complete two questionnaires. The first concerned with social background, behaviour and social adjustment, psychological factors and general health. The second dealt specifically with substance use, e.g. tobacco smoking, use of drugs and alcohol consumption. Cigarette smoking was classified into one of three levels (non-smokers, 1 10 cigarettes/day, >10 cigarettes/day). The conscripts were asked if they at least sometimes had been on medication for nervous problems, and an affirmative answer was used as a measure of psychological difficulties. All conscripts were seen by a physician who diagnosed any disorders physical or mental, according to the Swedish version of the International Classification of Disease (ICD), 8th revision (ICD-8). Conscripts with psychiatric disorders were also examined by a psychiatrist. Any psychiatrist diagnosed mental illness according to the ICD-8 classification was used as a second measure of mental well-being in the present investigation. Following specified instructions the variable emotional control was assessed through face-to-face interview with a psychologist at conscription in five levels. Low emotional control, defined as a score of 1 or 2 on a scale from 1 (lowest) to 5 (highest) was reported for 20% of the cohort, and were allocated to subjects suffering from documented reduced function due to psychosomatic symptoms, who had low levels of stress tolerance and/or were full of anxiety, had problems controlling nervousness and channelling aggression, and showed an incapacity for emotional commitment. The ratings were checked for inter-rater reliability, in order to maintain high quality. 17 Information on parental divorce, collected at conscription, was used as an indicator of conflicts among family members. 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. 15 Alcohol consumption in grams of 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 of at least 250 g of 100% alcohol/week, reporting the drinking of an eye-opener during a hangover, having been apprehended by police for drunkenness, or having often been drunk (the choices were: often, rather often, sometimes and never ). Follow-up data on smoking Members of the study group for this investigation were interviewed in at least one annual Survey of Living Conditions, randomly distributed between 1981 and 2002, depending solely on being sampled at random to a particular annual Survey of Living Conditions sample. In these surveys, respondents were asked if they were currently smokers or non-smokers. No information on the number of cigarettes smoked was available in these surveys. Figure 1 summarizes the study cohort and sub-cohort, and the conscription and subsequent surveys. Data analysis The representativeness of the sample of the conscription cohort for whom follow-up smoking data were available was

3 68 European Journal of Public Health Table 1 Prevalence (%) of risk factors reported at age 18 in 1969 in the full cohort and the sample Prevalence of conditions at age 18 Number Prevalence Smoking (%) Full cohort Sample Psychiatric diagnosis at Full cohort conscription Sample Medication for nervous Full cohort problems Sample Low emotional control Full cohort Sample Parental divorce Full cohort Sample Alcohol consumption Full cohort Sample Contact with police and Full cohort child welfare Sample Drug use Full cohort Sample Based on those included in the full conscription cohort The sample included those in the full conscription cohort who also participated in one or more Surveys of Living Conditions evaluated by comparing the conscription prevalence of smoking and the important measures of mental well-being at conscription between the subset with follow-up smoking data, and the full conscription cohort. The prevalence (%) of seven indicators of lower mental wellbeing measured in 1969 was calculated for groups with different smoking status at baseline survey in 1969 as well as at follow-up in For clarity of presentation, we used the following terminology to identify groups with differing smoking habits at conscription and then in subsequent surveys: never smokers; late smokers (those denying smoking at conscription, but reporting smoking on follow up); quitters (smokers at conscription who were no longer smokers at follow-up) and persistent smokers (reporting smoking both at conscription and at follow-up). The last group was further divided into those who were light smokers (1 10 cigarettes/ day) at conscription who were still smokers at follow-up, and heavy smokers (more than 10 cigarettes/day) at conscription who were still smokers at follow up. Prevalence ratios (PR) and 95% confidence intervals (CI) were used to compare the prevalence at conscription of the measures of mental wellbeing among groups with different smoking habits. Due to missing information for some variables the numbers from which the PR are calculated differs somewhat. Because of our interest in how childhood and adolescent mental health might affect quitting, we set quitters as the reference group, and compared persistent light and heavy smokers to them. Never-smokers were also compared to quitters in the same analyses. Results Of the 675 men with information on smoking status at conscription as well as during follow-up, 42.0% reported nonsmoking at conscription in The remaining 58.0% (391) were smokers. This result agrees very well with the data for the full cohort 41.4% were non-smokers in 1969 (table 1). There was also good agreement between the full cohort and the subcohort with respect to the distribution of the variables on mental health measured at the conscription survey, as would be expected if the Survey of Living Conditions sampling was truly random, and if there was no important refusal bias (table 1). Table 2 Change in smoking status from conscription survey to follow up One-half (48.8%) of the smokers at age 18 in the sub-cohort reported that they were non-smokers, when they were surveyed between 1981 and 2002 (table 2). Among the non-smokers at baseline, only 18 (6.3%) reported that they were smokers at follow-up in Because of this small number, these late smokers were not studied further. In contrast, about 94% of non-smokers at baseline remained non-smokers at followup. Smokers of 10 or less cigarettes per day at baseline were much more likely to be non-smokers at follow-up (56.6%) than were smokers of more than 10 cigarettes per day (only 38.2% reported being non-smokers at follow up). Thus, heavy smokers at conscription were less likely (38.2%/56.6% ¼ 0.68) to quit compared with light smokers. The prevalence of indicators of poor mental well-being at conscription was higher in persistent heavy smokers than in quitters. In contrast, persistent light smokers did not show important differences in mental well-being compared to quitters. This latter observation is limited though, by the fairly small numbers of persistent light smokers, and the resulting wide CI on PR in table 3. Compared to quitters, persistent heavy smokers were nearly three times as likely to have reported psychiatric medication use before age 18 (PR ¼ 2.8, 95% CI: ). Excess risks between 50% and 80% in persistent heavy smokers were also observed for: psychiatric diagnosis, low emotional control, parental divorce, risky use of alcohol and contact with police and child welfare authorities. Never smokers had generally better mental well-being at conscription than quitters (and also than persistent smokers). Non-smokers were less likely to report a psychiatric diagnosis than quitters (PR ¼ 0.6, 95% CI: ), markedly less likely to report risky use of alcohol (PR ¼ 0.2, 95% CI: ), and less likely to have reported childhood contact with policy or child welfare authorities and drug use (table 3). Discussion Smoking status at follow up, Smoking status at age 18, 1969 Non-smoker Smoker Total Non-smoker 93.7% (266) 6.3% (18) 100% (284) Smoker 48.8% (191) 51.2% (200) 100% (391) 1 10 cigs/day 56.6% (128) 43.4% (98) 100% (226) >10 cigs/day 38.2% (63) 61.8% (102) 100% (165) Percents of subjects (numbers) are shown based on 675 persons with information on smoking at the conscription examination in 1969 and at follow-up between In this longitudinal study, we found that smoking cessation at years of age was associated with indicators of mental well-being measured at age 18. We have previously shown that these same indicators of mental well-being were strongly associated with smoking at age For example, reported psychiatric medication use before age 18 was 3.6 times more prevalent in smokers of more than 20 cigarettes/day than in non-smokers, and intermediate levels of smoking showed intermediate prevalences of this mental health indicator. In the present longitudinal analysis, those who were heavy (more than 10 cigarettes/day) smokers at age 18 and did not quit smoking later in life reported more psychiatric medications, were given more psychiatric diagnoses, were determined by a psychologist to have lower emotional control, and reported more drug use, risky alcohol use, and childhood contact with

4 Smoking and mental health 69 Table 3 Prevalence (%) and prevalence ratios (PR) for indicators of mental wellbeing in categories of lifetime smoking behaviour Lifetime smoking category Never Quitter Persistent Light Persistent Heavy 1969 smoking status Non-smoker Smoker Smoker, 10 cig/day Smoker, > 10 cig/day smoking status Non-smoker Non-smoker Smoker Smoker n ¼ Psychiatric diagnosis, 1969 (n ¼ 657) Percent (n) 7.9% (21) 13.1% (25) 11.2% (11) 23.5% (24) PR (95% CI) 0.6 ( ) ( ) 1.8 ( ) Psychiatric medication, 1969 (n ¼ 651) Percent (n) 11.4% (30) 10.0% (19) 8.3% (8) 27.7% (28) PR (95% CI) 1.1 ( ) ( ) 2.8 ( ) Low emotional control, 1969 (n ¼ 650) Percent (n) 24.7% (65) 31.4% (59) 24.7% (24) 45.1% (46) PR (95% CI) 0.8 ( ) ( ) 1.4 ( ) Parental divorce, 1969 (n ¼ 643) Percent (n) 6.5% (17) 11.8% (22) 4.2% (4) 20.2% (20) PR (95% CI) 0.6 ( ) ( ) 1.7 ( ) Risky use of alcohol, 1969 Percent (n) 3.5% (9) 15.1% (28) 17.2% (16) 27.8% (27) PR (95% CI) 0.2 ( ) ( ) 1.8 ( ) Contact with police and child welfare, 1969 (n ¼ 652) Percent (n) 14.7% (39) 28.3% (53) 34.7% (34) 45.5% (46) PR (95% CI) 0.5 ( ) ( ) 1.6 ( ) Drug use, 1969 (n ¼ 622) Percent (n) 4.0% (10) 14.0% (25) 8.3% (8) 19.0% (18) PR (95% CI) 0.3 ( ) ( ) 1.4 ( ) Prevalence ratio, with 95% confidence interval. Reference: quitters police and child welfare authorities at conscription than those who quit smoking. These analyses were based on a small sample of the full cohort the result of chance intersection of the cohort with the respondents to an entirely separate series of random national surveys, the Swedish Surveys of Living Conditions. Despite the small sample of the cohort with follow up smoking data just over 1%, they were quite representative of the full cohort, with respect to the prevalence of smoking at baseline, as well as with respect to the measures of mental well-being. We are therefore confident that no serious bias has been introduced by the use of this sub-cohort. The numbers are too small for some analyses (starters were few, for example), but there was adequate precision for our main findings on the differences between quitters and persistent heavy smokers, as evidenced by moderately narrow CI for the PR (table 3). Our definition of smoking persistence was limited by being based on only two time points, and the self-reported nature of the smoking data. Nevertheless, we have no reasons to believe that misclassification had serious consequences for the validity of our findings. The baseline definition of who was a smoker was determined in 1969, just prior to the major public campaigns raising awareness of the hazards of use of tobacco. Thus, it is unlikely that there was serious under-reporting of smoking at that time. 18 In contrast, the surveys used to identify smokers who subsequently quit were conducted during a time period when the dangers of smoking were well publicized. It is possible, therefore, that some participants in the follow-up surveys claimed to be non-smokers who were, in fact, still smoking. This misclassification of persistent smokers as quitters might tend to diminish differences in prevalence of the mental health measures between quitters and persistent smokers, thus suggesting that the true differences might have been greater than those observed. The psychiatric diagnoses given at the conscription survey was classified according to the ICD, version 8. At present time, the updated version number 10 of ICD is in use. However, we believe that the measure of psychiatric illness used in this study quite well captures what would have been found using a more updated version of ICD, although the specific diagnoses would differ somewhat. All conscripts met with a psychologist for a face-to-face interview, in order to assess level of emotional control. The purpose was to collect information, in order classify the 18-year old men into military position (e.g. privates and officers) for their compulsory service. We are not fully aware of a similar measure used in personality research today. However, we have previously reported strong associations between the measure of low emotional control and smoking, 14 alcoholism, 19 early retirement 20 and mortality. 16 Level of smoking Many studies have reported that heavy smokers have lower quit rates than light smokers. 4,7,21 This pattern was confirmed by our results. The detailed psychiatric history taken at conscription enabled us to add to this observation by showing that a higher level of smoking at time of conscription was associated with mental health problems at that time as well as with smoking persistence during the follow-up period. Because of the rather small size of our sub-cohort, we had to divide smokers into heavy and light at a cut-point of 10 cigarettes/day. In many studies cigarettes/day is considered moderate smoking, and the term heavy is used for greater than 20 or even 30 cigarettes/day. Thus, when comparing our findings to others, it may be more appropriate to consider our higher smoking group as corresponding to moderate and heavy smoking. Persistent smokers of 10 or fewer cigarettes/day were not very different from quitters with respect to their mental health indicators at age 18. Individuals smoking only occasionally may not be addicted to nicotine, and this subgroup may also have different personality traits and experiences protecting them from mental health problems. 6,22

5 70 European Journal of Public Health The causal question The prospective nature of our data was helpful in distinguishing between the two alternative explanations for the observation that quitters have better mental wellbeing than continuing smokers. As noted in the introduction, it has been argued that either: (i) those with high mental well-being are more successful at smoking cessation, or (ii) improved mental well-being results from smoking cessation. In these data, we are confident that our measures of mental well-being long preceded a decision to quit smoking, and so the first explanation is supported by our data, while the second is not. It remains possible that there is also an improvement in mental well-being that results from smoking cessation. Due to lack of follow-up data on mental health we were not able to investigate the possible impact of the second explanation. However, we believe that the most parsimonious interpretation is that it is more difficult for those with poor mental well-being than for those with high mental well-being in late adolescence to quit smoking later in life. Conclusion The results of this study lend support to a causal explanation in which those with good mental health in late adolescence were more successful at later smoking cessation and those with poor mental health in late adolescence more often persisted in smoking. The results do not support (but cannot be used directly to disprove) the hypothesis that smoking cessation promotes increased mental health. Acknowledgement This study was supported by the Swedish Council for Working Life and Social Research (Project No ) Conflict of interest: None declared. Key points Several studies have reported an association between smoking and psychiatric illness. Those who stop smoking report better mental health than persistent smokers. 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