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How intelligence and emotional control are related to suicidal behavior across the life course – A register-based study with 38-year follow-up

Published online by Cambridge University Press:  09 October 2019

Nora Hansson Bittár*
Affiliation:
Department of Clinical Neuroscience, Karolinska Institutet, Stockholm, Sweden
Daniel Falkstedt
Affiliation:
Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden
Alma Sörberg Wallin
Affiliation:
Department of Public Health Sciences, Karolinska Institutet, Stockholm, Sweden
*
Author for correspondence: Nora Hansson Bittár, E-mail: nora.hansson@gmail.com
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Abstract

Background

Both low intelligence and low emotional control have previously been linked to a higher risk of suicide, but it is unknown whether the associations apply consistently over the life course.

Methods

The study was based on data on intelligence and emotional control, collected from 48 738 Swedish men conscripted in 1969–1970, at ages 18–20 years. The data were linked to national registers giving information on subsequent suicidal behavior (completed and attempted suicide) up to the age of 59 years. The associations were investigated using logistic regression and Cox proportional hazards regression models, with adjustment for childhood socioeconomic status.

Results

Intelligence and emotional control assessed in late adolescence both showed robust inverse associations with suicidal behavior over the 38-year follow-up. However, while the association between lower intelligence and higher rate of suicidal behavior remained the same throughout (~40% increased hazard per unit on a five-level scale), the association between lower emotional control and suicidal behavior was substantially stronger in early adulthood (~100% increased hazard per unit) than in late middle age (~30% increased hazard per unit).

Conclusions

The study adds to previous research by showing that the association between poor emotional control and subsequent suicide risk in men becomes weaker over the life course, while the association between low intelligence and suicide risk seems to be constant. The particularly high suicide risk of young men with poor emotional control may motivate targeted prevention efforts.

Type
Original Articles
Creative Commons
Creative Common License - CCCreative Common License - BY
This is an Open Access article, distributed under the terms of the Creative Commons Attribution licence (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted re-use, distribution, and reproduction in any medium, provided the original work is properly cited.
Copyright
Copyright © The Author(s) 2019

Introduction

Suicide is one of the leading causes of death worldwide, and approximately one million people die each year from suicide (World Health Organization, 2012). Like many other health-related outcomes, suicide is not the consequence of a single disease factor. Rather, there are multiple factors that contribute to completed and attempted suicide (here denoted as suicidal behavior), such as the presence of psychiatric disorders, physical illnesses, impulsive behaviors, and life stressors (Gunnell and Lewis, Reference Gunnell and Lewis2005). Previously, it has been shown that both lower level of intelligence and higher level of neuroticism, or low emotional control, are related to an increased risk of suicidal behavior (Allebeck et al., Reference Allebeck, Allgulander and Fisher1988; Brezo et al., Reference Brezo, Paris and Turecki2006; Batty et al., Reference Batty, Whitley, Deary, Gale, Tynelius and Rasmussen2010; Gravseth et al., Reference Gravseth, Mehlum, Bjerkedal and Kristensen2010; Sörberg et al., Reference Sörberg, Allebeck, Melin, Gunnell and Hemmingsson2013). However, little is yet known about these associations from a life-course perspective, with regards to whether the associations change or remain stable over time.

Intelligence is a general ability that reflects a broad and deep capability of understanding our surroundings, which involves the ability to reason, plan, solve problems, think abstractly, comprehend complex ideas, learn quickly, and learn from experience (Gottfredson, Reference Gottfredson1997). Research in recent years has provided extensive evidence that intelligence is an important predictor of major life outcomes, such as educational attainment, occupation, and health, and also suicidal behavior (Batty et al., Reference Batty, Whitley, Deary, Gale, Tynelius and Rasmussen2010; Sörberg et al., Reference Sörberg, Allebeck, Melin, Gunnell and Hemmingsson2013; Plomin and Deary, Reference Plomin and Deary2015). Moreover, intelligence is fairly stable over the life course. For example, in a Scottish cohort of about 1000 women and men, the raw stability coefficient for people who completed the same intelligence test at age 11 and age 70 was on average 0.67 (Gow et al., Reference Gow, Johnson, Pattie, Brett, Roberts, Starr and Deary2011).

Emotional control is a construct aimed to capture factors such as susceptibility to stress, anxiety, psychosomatic symptoms, and poor control over nervousness and aggression (Potijk et al., Reference Potijk, Janszky, Reijneveld and Falkstedt2016). This construct has not been widely used in research on suicidal behavior but shows great similarities with one of the big five personality dimensions, namely neuroticism, which is associated with anxiety, anger, depression, impulsiveness and vulnerability (Chamorro-Premuzic, Reference Chamorro-Premuzic2016). Although emotional control and neuroticism are not identical constructs, they are highly overlapping. Both concern stable personality traits related to emotional stability, and both have been shown to be associated with an increased risk of suicidal behavior (Allebeck et al., Reference Allebeck, Allgulander and Fisher1988; Brezo et al., Reference Brezo, Paris and Turecki2006; Wiktorsson et al., Reference Wiktorsson, Berg, Billstedt, Duberstein, Marlow, Skoog and Waern2013). The societal economic burden attributed to neuroticism exceeds that of common mental disorders (Cuijpers et al., Reference Cuijpers, Smit, Penninx, de Graaf, ten Have and Beekman2010).

Neuroticism has been found to be mostly stable over the life course, but, according to a meta-analysis, a decline in the population mean of neuroticism takes place during late adolescence and early adulthood (Roberts et al., Reference Roberts, Walton and Viechtbauer2006). After the age of 30, however, the level of neuroticism tends to regain stability at the group level (Roberts et al., Reference Roberts, Walton and Viechtbauer2006). Specifically, test-retest consistency increases with age from 0.45 during adolescence to 0.60 during young and middle adulthood (Roberts and DelVecchio, Reference Roberts and DelVecchio2000).

Even though both lower intelligence and higher neuroticism have previously been linked to an increased risk of subsequent suicidal behavior (Allebeck et al., Reference Allebeck, Allgulander and Fisher1988; Brezo et al., Reference Brezo, Paris and Turecki2006; Batty et al., Reference Batty, Whitley, Deary, Gale, Tynelius and Rasmussen2010; Gravseth et al., Reference Gravseth, Mehlum, Bjerkedal and Kristensen2010; Sörberg et al., Reference Sörberg, Allebeck, Melin, Gunnell and Hemmingsson2013), little is yet known about those associations from a life-course perspective. Risk factors for suicide might act differently over the life course (Gunnell and Lewis, Reference Gunnell and Lewis2005) and, likewise, the roles of intelligence and emotional control might change over time. Indeed, we have found previously that the association between intelligence measured at age 18–20 and subsequent depression was particularly strong in young adulthood, but then attenuated considerably towards late middle age (Lager et al., Reference Lager, Melin, Hemmingsson and Wallin2017). Previous researchers have stressed that knowledge of risk factors is essential for the effective prevention of suicidal behavior (Gunnell and Lewis, Reference Gunnell and Lewis2005; Nock et al., Reference Nock, Borges, Bromet, Cha, Kessler and Lee2008). From that perspective, understanding of the long-term associations between individual differences and suicidal behavior should be of greatest interest.

Aim

The aim of this study was to investigate how the associations between intelligence and emotional control in early adulthood and subsequent suicidal behavior develop over time. We examined those associations in a Swedish male cohort with measurements from military conscription in 1969–1970. The cohort information was linked to national register data on suicidal behavior, with childhood socioeconomic status (SES) treated as a potential confounder, and followed over 38 years, up to the age of 59.

Method

Study population

The study was based on data collected at compulsory conscription for Swedish military service in 1969 and 1970. About 97–98% of all Swedish men were conscripted at that time; the remaining 2–3% were in most cases exempted due to severe disability or congenital disorders. The cohort consisted of 49 321 men born 1949–1951 (aged 18–20). Approximately 2% of all the men who were conscripted during those years were born prior to 1949, and were excluded from the data set in order to obtain as homogeneous a cohort as possible. All information was anonymized before it was made available for research to protect the integrity of the individuals. The research has been approved by the ethical committee at Karolinska Institutet (numbers 2004/5:9–639/5 and 2010/604:32).

From the original cohort, 583 men were excluded due to missing data on intelligence (n = 75) and/or emotional control (n = 396), and/or death or emigration prior to the start of follow-up (n = 175), which left 48 738 men (98.8%) for analysis.

Material and procedure

Conscription in Sweden

The Swedish conscription process included physical and medical assessments, a test of intelligence, an interview with a psychologist, and questionnaires that covered social background, psychological and psychosomatic problems, and adjustment and substance use (Allebeck et al., Reference Allebeck, Allgulander and Fisher1988).

Intelligence

Intelligence was measured at conscription through a multidimensional test, which included four subtests examining verbal, logic-inductive and visuospatial ability, and technical comprehension. The outcomes were converted into a global score with a normal (Gaussian) distribution on a nine-level scale. The test battery was designed to measure general intelligence, and used primarily to find a position with appropriate learning demands and predict the conscript's ability to profit from education within the military (Ross, Reference Ross1988). A detailed description of the test is presented elsewhere (Karlsson et al., Reference Karlsson, Ahlborg, Dalman and Hemmingsson2010; Sörberg Wallin, Reference Sörberg Wallin2015). Test-retest reliability was 0.81 for the global score of a group of 107 men retested after one to three years (Ross, Reference Ross1988). In the current study, the nine-level scale was converted into a five-level scale in order to match the scale of emotional control. Following conversion, the scale approximately corresponded to IQ bands of <82, 82–95, 96–110, 111–126, and >126.

Emotional control

Assessment of emotional control was made through a semi-structured interview administered by a trained psychologist. The interview took about 20–30 min, and a summary of the interview process is provided elsewhere (Potijk et al., Reference Potijk, Janszky, Reijneveld and Falkstedt2016; Ross, Reference Ross1988). The overall aim of the interview was to measure the conscript's suitability for military service, including tolerance of mental stress. Emotional control was measured as situation-specific regulation of emotions. The psychologist asked the conscripts how they emotionally responded to important events and situations experienced in childhood and adolescence, for example personal conflicts or stress at school or work. Based on the responses, the psychologists rated emotional control on a scale ranging from one (very low) to five (very high). Higher scores on emotional control were allocated to conscripts with high stress tolerance, low anxiety and control over nervousness and aggression, whereas lower scores were allocated to subjects with psychosomatic symptoms, low levels of stress tolerance, anxiety and problems in controlling nervousness and aggression (Stenbacka and Jokinen, Reference Stenbacka and Jokinen2015). The inter-rater reliability of the psychologists' ratings has been found to be as high as 0.85 (Lilieblad and Ståhlberg, Reference Lilieblad and Ståhlberg1977).

Suicidal behavior

The conscription data were linked to register data on suicidal behavior, which encompasses both completed and attempted suicide. Information about completed suicides during the period 1973–2008 was collected from the National Cause of Death Register, and information about suicide attempts for the same time period was obtained from the National Hospital Discharge Register. The variables were classified following the International Classification of Disease (ICD) codes for suicide and suicide attempt (ICD-8/9: E950-9; ICD-10: X60-X84), and for events of undetermined intent (ICD-8/9: E980-9; ICD-10: Y10-Y34). The latter was included since previous research has shown that most deaths from events of undetermined intent are likely to be suicides (Jiang et al., Reference Jiang, Hadlaczky and Wasserman2014).

Socioeconomic status

Information on childhood SES was collected from the national census in 1960. The SES categories were based on the occupation of the father, if available, but otherwise the mother. The six categories were: (1) unskilled workers, (2) skilled workers, (3) assistant non-manual employees, (4) non-manual employees at intermediate or higher level, (5) farmers, and (6) others or those with no occupation reported.

Statistical analysis

The associations between intelligence and emotional control at conscription and subsequent suicidal behavior were first estimated for the full follow-up period using Cox proportional hazard models, yielding hazard ratios (HRs) with 95% confidence intervals (CIs). The conscripts were followed until emigration, death, or the first event of suicidal behavior, or until the end of 2008, whichever came first.

The follow-up period was then divided into four approximate decades (1973–1979, 1980–1989, 1990–1999, and 2000–2008). Thereafter, logistic regressions yielding odds ratios (ORs) were used to investigate the associations of intelligence and emotional control with suicidal behavior for each decade separately in the men who were alive and had not emigrated at the start of each period. Tests of interaction with time were performed to test formally whether the associations remained stable over time. The independent variables, intelligence and emotional control, were modeled as continuous variables, with HRs and ORs given for each step decrease on the scales of intelligence and emotional control, and also as categorical variables to obtain HRs and ORs for each level, with the highest levels as the reference categories. All analyses were adjusted for childhood SES. We then repeated the analyses with mutual adjustment for intelligence and emotional control to separate their associations with suicidal behavior from each other.

Additionally, we performed sensitivity analyses by excluding completed suicide from the dependent variable, and also by excluding events with undetermined intent. These analyses were performed to check whether the results were robust to any differences between attempted and completed suicide and between undetermined and certain suicidal intent. All analyses were performed using SAS 9.4 (SAS Institute, Inc., Cary, NC, USA 2012).

Results

During the total follow-up period (1973–2008), 1725 of the men (3.5%) had a suicidal-behavior event (493 completed and 1232 attempted suicides as their first event). The numbers of men with a suicidal-behavior event across the levels of intelligence and emotional control are shown in Table 1.

Table 1. Associations of intelligence (IQ) and emotional control (EC) in 1969/1970 with suicidal behavior 1973–2008

Parts a and c: Hazard ratios (HRs; marked with ‘) with 95% confidence intervals (CIs) for the entire follow-up period, modelling IQ and EC as categorical variables. Parts b and d: HRs for the entire follow-up and odds ratios (ORs; marked with ‘§’) for the separate time periods, with 95% CIs, modelling IQ and EC as continuous variables. All models are adjusted for childhood SES.

a One (1) represents the lowest level and five (5) the highest level of intelligence and emotional control. Level 5 is the reference category in these analyses (HR = 1)

The associations of intelligence and emotional control with suicidal behavior followed dose-response patterns, as shown in Table 1 (parts a and c, IQ and EC in units, modelled as categorical variables). For example, men in the lowest intelligence category (1) had a six-fold higher risk of suicidal behavior (HR and 95% CI 6.29, 4.48–8.83), and men in the second lowest category (2) had a four-fold higher risk of suicidal behavior (4.02, 2.89–5.60), compared with men in the highest intelligence category (5). In a similar manner, men in the lowest category of emotional control (1) had an almost seven-fold higher risk of suicidal behavior (6.64, 4.75–9.28), and men in the second lowest category (2) had a three-fold higher risk of suicidal behavior (3.46, 2.50–4.78), compared with men in the highest category (5).

When modeling intelligence and emotional control as continuous variables (parts b and d in Table 1, IQ and EC per unit decrease), suicidal behavior between 1973 and 2008 was associated with both lower intelligence (HR and 95% CI 1.54, 1.46–1.61 per unit decrease on the five-level scale) and lower emotional control (1.68, 1.60–1.76), after adjustment for childhood SES. This implies that one unit lower intelligence on the five-level scale was associated with a 54% higher risk of suicidal behavior and one unit lower emotional control was associated with a 68% higher suicidal risk. In the sensitivity analyses (both modeling intelligence and emotional control as continuous variables, per unit decrease; not shown in the table), when completed suicide was excluded from the dependent variable, the HR for intelligence (1.61, 1.52–1.70 per unit decrease) and the HR for emotional control (1.77, 1.67–1.88 per unit decrease) were only slightly higher; and excluding events of undetermined intent gave quite similar results to those of the main analysis (1.57, 1.47–1.67 for intelligence, and 1.73, 1.62–1.86 for emotional control, per unit decrease). Further, a crude analysis without controlling for childhood SES yielded very similar results (1.53, 1.46–1.60 for intelligence and 1.70, 1.61–1.78 for emotional control, per unit decrease), implying that childhood SES was not a confounder that would explain the associations.

When analyzed over the separate follow-up periods, the association between intelligence and suicidal behavior remained fairly stable over the life course, whereas the association between emotional control and suicidal behavior gradually weakened, see Table 1 (parts b and d; the continuous variables were used in these models). For example, one lower unit of intelligence was associated with a 65% higher risk of suicidal behavior during the first follow-up period (OR and 95% CI 1.65, 1.49–1.82) and a 53% higher risk of suicidal behavior during the last follow-up period (1.53, 1.39–1.69). On the other hand, one lower unit of emotional control was associated with a 117% higher risk of suicidal behavior during the first follow-up period (2.17, 1.95–2.40) but with only a 44% higher suicidal risk during the fourth and last follow-up period (1.44, 1.30–1.59). A significance test confirmed that the association with emotional control weakened over the follow-up period (p < 0.0001 for interaction with time). In the models with mutual adjustments for intelligence and emotional control, the associations were weakly to moderately attenuated but the difference between them over the total follow-up period remained, see Fig. 1. The exact estimates and 95% CIs are shown in online Supplementary Table S1.

Fig. 1. Associations between suicidal behavior and intelligence and emotional control, respectively, with adjustment for each other and for childhood SES. ORs with 95% CIs for suicidal behavior are given for a one step decrease on the five-level scales of intelligence and emotional control for the separate follow-up periods. The time periods end at about 10, 20, 30 and 40 years after conscription, respectively, and correspond with approximate age intervals of 22–28 years, 29–38 years, 39–48 years and 49–58 years.

Discussion

In sum, our analyses showed that the association between low intelligence and suicidal behavior was fairly constant over the follow-up period to age 59 in this cohort of Swedish men, whereas the association between low emotional control and suicidal behavior weakened with increasing age. Mutual adjustment for intelligence and emotional control attenuated the associations somewhat but did not attenuate the difference between them. Adjustment for socioeconomic status during childhood had only marginal effects on the results.

Findings in relation to previous research

Suicidal behavior has been linked to lower intelligence and higher neuroticism (which is similar to low emotional control) in some previous studies (Brezo et al., Reference Brezo, Paris and Turecki2006; Osler et al., Reference Osler, Andersen and Nordentoft2008; Gravseth et al., Reference Gravseth, Mehlum, Bjerkedal and Kristensen2010; Wiktorsson et al., Reference Wiktorsson, Berg, Billstedt, Duberstein, Marlow, Skoog and Waern2013), including a few separate studies of the same cohort of men as in the current study (Allebeck et al., Reference Allebeck, Allgulander and Fisher1988; Batty et al., Reference Batty, Whitley, Deary, Gale, Tynelius and Rasmussen2010; Sörberg et al., Reference Sörberg, Allebeck, Melin, Gunnell and Hemmingsson2013).

We are not aware of any previous studies focusing on changes in these associations over the life course, but a previous study using the same cohort showed that lower intelligence and a higher risk of hospitalization for major depression had a weakening association over the 38-year follow-up (Lager et al., Reference Lager, Melin, Hemmingsson and Wallin2017). Since depression is a well-known risk factor for suicide (Lesage et al., Reference Lesage, Boyer, Grunberg, Vanier, Morissette and Loyer1994), it is somewhat surprising that we found the association between higher intelligence and lower risk of suicidal behavior to remain stable over the life course. Nevertheless, risk factors for suicidal behavior are not identical to those for psychiatric disorders and their impact during the life span may differ (Gunnell and Lewis, Reference Gunnell and Lewis2005), which might explain the divergent findings.

Possible explanations and implications

Although the associations of both intelligence and emotional control with suicidal behavior remained after adjustment, it is not necessarily the case that low intelligence and low emotional control are immediate causes of suicidal behavior. To some extent, these psychological differences between individuals may also predict suicidal behavior along indirect pathways. Several potential mechanisms underlying the associations of intelligence and neuroticism with suicidal behavior have been presented in previous research. For example, Gottfredson and Deary (Reference Gottfredson and Deary2004) stress that intelligence may enhance individuals' care for their own health, since it represents learning, reasoning and problem-solving skills. Further, lower neuroticism (Gunthert et al., Reference Gunthert, Cohen and Armeli1999), and presumably also higher intelligence, are associated with more adaptive coping strategies, which might increase resilience in the face of stressful life events and thereby prevent suicidal behavior (Andersson et al., Reference Andersson, Allebeck, Gustafsson and Gunnell2008; Wiktorsson et al., Reference Wiktorsson, Berg, Billstedt, Duberstein, Marlow, Skoog and Waern2013). Also, it has been suggested that individuals with high neuroticism are more likely than others to experience stressful life events, and also gain less social support (Kendler et al., Reference Kendler, Gardner and Prescott2003; Deary et al., Reference Deary, Weiss and Batty2010), which may help to explain their increased risk of suicidal behavior.

One of the main findings of this study was that the association between intelligence and suicidal behavior remained constant over the entire follow-up period, while the association between emotional control and suicidal behavior was particularly strong in young adulthood and then weakened across the four periods. Largely, the two characteristics were associated with suicidal behavior independently of each other, as shown in the mutually adjusted models. Each, however, accounted for some of the other characteristic's association with suicidal behavior: for emotional control to a greater extent in the first follow-up periods, and for intelligence to an increasing extent in the later periods. Thus, mutual adjustment did not reduce the difference in time trends between intelligence and emotional control.

The gradual weakening of the association between emotional control and suicidal behavior may have some different potential explanations. One is that emotional control is more variable than intelligence from a life-course perspective. This idea is supported by previous research showing that there is a decrease in the population mean of neuroticism during late adolescence while intelligence seems to be more stable (Roberts et al., Reference Roberts, Walton and Viechtbauer2006). Similarly, previous research has shown that the presence of negative emotions, such as stress and anger, steeply decline from the early 20s, and that older adults are less emotionally reactive to stressors and less engaged in destructive conflict strategies than younger adults (Stone et al., Reference Stone, Schwartz, Broderick and Deaton2010; Mather, Reference Mather2012). Another potential explanation for why the association weakens is that stressful circumstances or life events during the years leading up to the conscription examination, e.g. in school (Lager et al., Reference Lager, Melin, Hemmingsson and Wallin2016), could both have had a negative impact on emotional control, as rated in the psychologists' interviews at conscription, and increased the incidence of suicidal behaviors for a time following the conscription examination. This would be consistent with findings showing that some of the fluctuations in neuroticism over time seems to be associated with life events (Ormel et al., Reference Ormel, Riese and Rosmalen2012). In principle, however, the conscription interview was designed to measure a personality trait, not an emotional state.

Our results highlight the possibility that low intelligence and – less surprisingly – poor emotional control influence the risk of suicide. The importance of this for suicide-preventive work may be worth investigating further. Other studies have discussed how low intelligence and poor emotional control also increase the likelihood of ending up in difficult circumstances, e.g. with low education or problematic social relations (Roberts et al., Reference Roberts, Kuncel, Shiner, Caspi and Goldberg2007; Deary et al., Reference Deary, Weiss and Batty2010). In accordance with this, studies in which we ourselves were involved have suggested that low socioeconomic status, and also risky behaviors, in young adulthood help to explain the relationships between intelligence, emotional control and health outcomes later in life (Sörberg et al., Reference Sörberg, Allebeck, Melin, Gunnell and Hemmingsson2013; Potijk et al., Reference Potijk, Janszky, Reijneveld and Falkstedt2016). In particular, our results may justify paying increased attention to the evidence that neuroticism and poor emotional control may contribute to high but eventually diminishing rates of harmful behaviors, including suicide, in young adult men. Access to treatment for the young may have to be given priority, since there is some evidence that neurotic problems can be reduced, e.g. with the help of cognitive behavioral therapy (CBT) and similar forms of psychotherapy (Jorm, Reference Jorm1989; Tang et al., Reference Tang, DeRubeis, Hollon, Amsterdam, Shelton and Schalet2009).

On the other hand, one possible reason for the long-term association between intelligence and suicidal behavior is that intelligence is robustly associated with attained education and socioeconomic position in adulthood (Plomin and Deary, Reference Plomin and Deary2015). These factors have been found to explain substantial proportions of the association between intelligence in youth and suicidal behavior in adulthood (Sörberg et al., Reference Sörberg, Allebeck, Melin, Gunnell and Hemmingsson2013; Sörberg Wallin et al., Reference Sörberg Wallin, Allebeck, Gustafsson and Hemmingsson2018a). They may be relevant to prevention at the societal level, not least because socioeconomic factors contribute considerably to suicide risk at the population level (Li et al., Reference Li, Page, Martin and Taylor2011). Of note is that this pathway might be more important for suicide prevention in men than in women; in women, low intelligence seems to be associated with suicide attempt (Sörberg Wallin et al., Reference Sörberg Wallin, Zeebari, Lager, Gunnell, Allebeck and Falkstedt2018b) but not death from suicide (Andersson et al., Reference Andersson, Allebeck, Gustafsson and Gunnell2008; Calvin et al., Reference Calvin, Batty, Der, Brett, Taylor, Pattie, Čukić and Deary2017; Sörberg Wallin et al., Reference Sörberg Wallin, Allebeck, Gustafsson and Hemmingsson2018a). The fact that gender differences are observed in these relationships further supports the hypothesis that social and socioeconomic factors are involved as mediators or moderators in the associations.

Strengths and limitations

There are several strengths to this study. The study population is strongly representative of the Swedish population of men who were born in 1950 and 1951, since nearly all men participated in compulsory conscription at that time. The exposure variables were measured using standardized test batteries and semi-structured interviews following manuals, and the outcome variables are based on national records with high reliability (Lilieblad and Ståhlberg, Reference Lilieblad and Ståhlberg1977; Ross, Reference Ross1988). Further, the 38-year follow-up period enabled us to follow the men in the cohort over a substantial part of their lives.

There are, however, two aspects of this study that limits its generalizability. First, we cannot generalize the results to women since only men were obliged to participate in conscription. Second, the results cannot be directly extrapolated to other settings partly because suicidal behavior differs between cultures (Nock et al., Reference Nock, Borges, Bromet, Cha, Kessler and Lee2008). Therefore, generalizations to other populations should be made with these limitations in mind. Further, our outcome variable, suicidal behavior, includes both completed and attempted suicide. This merged variable has been used in previous studies of the same cohort (Åberg et al., Reference Åberg, Nyberg, Torén, Sörberg, Kuhn and Waern2014), but since suicide attempt is far more frequent than completed suicide (Leon et al., Reference Leon, Friedman, Sweeney, Brown and Mann1990), and behavior associated with completed suicide may differ from behavior associated with suicide attempt, the merger might seem debatable. However, because our data include only severe suicide attempts that have led to hospitalization, it can be assumed that attempted and completed suicides are quite similar in the present study. In our analyses, the estimates were only slightly higher when completed suicide was excluded from the dependent variable. Lastly, intelligence and emotional control were measured at one point in time only. While intelligence is quite stable over the life course (Gow et al., Reference Gow, Johnson, Pattie, Brett, Roberts, Starr and Deary2011), personality aspects such as emotional control are more variable. Data with repeated measures of personality aspects are needed to directly investigate how changes in these measures might explain changes in their relationship with suicidal behavior.

Conclusions

In line with previous research, this study confirms that low intelligence and low emotional control are both associated with a higher risk of suicidal behavior among men. Further, this study adds to previous research by showing that the association between intelligence and suicidal behavior seems constant over the life course, whereas the association between emotional control and suicidal behavior may become considerably weaker over time. The particularly high suicide risk of young men with poor emotional control may motivate targeted prevention efforts.

Supplementary material

The supplementary material for this article can be found at https://doi.org/10.1017/S0033291719002423

Acknowledgements

We would like to thank Tomas Hemmingsson for providing data and for helpful advice.

Financial support

This research was funded by Forte, grant numbers 2015-00057 and 2017-00173.

Conflict of interest

None.

Ethical standards

The authors assert that all procedures contributing to this work comply with the ethical standards of the relevant national and institutional committees on human experimentation and with the Helsinki Declaration of 1975, as revised in 2008. Because of the character of the database, the normal requirement for written consent was waived. Instead, all data were anonymized before they were made available for research in order to protect the integrity of the individuals, and the data were handled in a careful and sensitive way. Further, studies of individual differences in intelligence, personality and suicide may be controversial because they highlight inequalities between individuals. However, gaining knowledge about how individual differences in intelligence and emotional control are associated with suicidal behavior will hopefully help us to reduce inequalities and prevent suicides in the long run.

References

Åberg, MAI, Nyberg, J, Torén, K, Sörberg, A, Kuhn, HG and Waern, M (2014) Cardiovascular fitness in early adulthood and future suicidal behaviour in men followed for up to 42 years. Psychological Medicine 44, 779788.CrossRefGoogle Scholar
Allebeck, P, Allgulander, C and Fisher, LD (1988) Predictors of completed suicide in a cohort of 50465 young men: role of personality and deviant behaviour. British Medical Journal 297, 176178.CrossRefGoogle Scholar
Andersson, L, Allebeck, P, Gustafsson, JE and Gunnell, D (2008) Association of IQ scores and school achievement with suicide in a 40-year follow-up of a Swedish cohort. Acta Psychiatrica Scandinavica 118, 99105.CrossRefGoogle Scholar
Batty, GD, Whitley, E, Deary, IJ, Gale, CR, Tynelius, P and Rasmussen, F (2010) Psychosis alters association between IQ and future risk of attempted suicide: cohort study of 1 109 475 Swedish men. British Medical Journal 340, c2506.10.1136/bmj.c2506CrossRefGoogle Scholar
Brezo, J, Paris, J and Turecki, G (2006) Personality traits as correlates of suicidal ideation, suicide attempts, and suicide completions: a systematic review. Acta Psychiatrica Scandinavica 113, 180206.CrossRefGoogle Scholar
Calvin, CM, Batty, GD, Der, G, Brett, CE, Taylor, A, Pattie, A, Čukić, I and Deary, IJ (2017) Childhood intelligence in relation to major causes of death in 68 year follow-up: prospective population study. British Medical Journal 357, j2708.CrossRefGoogle Scholar
Chamorro-Premuzic, T (2016) Personality and Individual Differences (3rd ed.), pp. 5354. Glasgow: John Wiley & Sons.Google Scholar
Cuijpers, P, Smit, F, Penninx, BW, de Graaf, R, ten Have, M and Beekman, AT (2010) Economic costs of neuroticism: a population-based study. Archives of General Psychiatry 67, 10861093.CrossRefGoogle Scholar
Deary, IJ, Weiss, A and Batty, GD (2010) Intelligence and personality as predictors of illness and death how researchers in differential psychology and chronic disease epidemiology are collaborating to understand and address health inequalities. Psychological Science in the Public Interest 11, 5379.CrossRefGoogle Scholar
Gottfredson, LS (1997) Mainstream science on intelligence: an editorial with 52 signatories, history, and bibliography. Intelligence 24, 1323.CrossRefGoogle Scholar
Gottfredson, LS and Deary, IJ (2004) Intelligence predicts health and longevity, but why? Current Directions in Psychological Science 13, 14.CrossRefGoogle Scholar
Gow, AJ, Johnson, W, Pattie, A, Brett, CE, Roberts, B, Starr, JM and Deary, IJ (2011) Stability and change in intelligence from age 11 to ages 70, 79, and 87: the Lothian Birth Cohorts of 1921 and 1936. Psychology and Aging 26, 232.10.1037/a0021072CrossRefGoogle Scholar
Gravseth, HM, Mehlum, L, Bjerkedal, T and Kristensen, P (2010) Suicide in young Norwegians in a life course perspective: population-based cohort study. Journal of Epidemiology and Community Health 64, 407412.CrossRefGoogle Scholar
Gunnell, D and Lewis, G (2005) Studying suicide from the life course perspective: implications for prevention. The British Journal of Psychiatry 187, 206208.CrossRefGoogle Scholar
Gunthert, KC, Cohen, LH and Armeli, S (1999) The role of neuroticism in daily stress and coping. Journal of Personality and Social Psychology 77, 10871100.CrossRefGoogle Scholar
Jiang, GX, Hadlaczky, G and Wasserman, D (2014) Självmord i Sverige–Data: 19802013. Nationellt centrum för suicidforskning och prevention av psykisk ohälsa (NASP) vid Karolinska Institutet, Stockholm.Google Scholar
Jorm, AF (1989) Modifiability of trait anxiety and neuroticism: a meta-analysis of the literature. Australian & New Zealand Journal of Psychiatry 23, 2129.CrossRefGoogle Scholar
Karlsson, H, Ahlborg, B, Dalman, C and Hemmingsson, T (2010) Association between erythrocyte sedimentation rate and IQ in Swedish males aged 18–20. Brain, Behavior, and Immunity 24, 868873.CrossRefGoogle Scholar
Kendler, KS, Gardner, CO and Prescott, CA (2003) Personality and the experience of environmental adversity. Psychological Medicine 33, 11931202.CrossRefGoogle Scholar
Lager, A, Seblova, D, Falkstedt, D and Lövden, M (2016) Cognitive and emotional outcomes after prolonged education: a quasi-experiment on 320 182 Swedish boys. International Journal of Epidemiology 46, 303311.Google Scholar
Lager, E, Melin, B, Hemmingsson, T and Wallin, AS (2017) The evolving relationship between premorbid intelligence and serious depression across the lifespan–A longitudinal study of 43,540 Swedish men. Journal of Affective Disorders 211, 3743.CrossRefGoogle Scholar
Leon, AC, Friedman, RA, Sweeney, JA, Brown, RP and Mann, JJ (1990) Statistical issues in the identification of risk factors for suicidal behavior: the application of survival analysis. Psychiatry Research 31, 99108.CrossRefGoogle Scholar
Lesage, AD, Boyer, R, Grunberg, F, Vanier, C, Morissette, R and Loyer, M (1994) Suicide and mental disorders: a case-control study of young men. The American Journal of Psychiatry 151, 1063.Google Scholar
Li, Z, Page, A, Martin, G and Taylor, R (2011) Attributable risk of psychiatric and socio-economic factors for suicide from individual-level, population-based studies: a systematic review. Social Science & Medicine 72, 608616.CrossRefGoogle Scholar
Lilieblad, B and Ståhlberg, A (1977) Reliabilitet hos psykologiska bedömningar vid inskrivningsprovning. FOA-rapport C, 55011-H7.Google Scholar
Mather, M (2012) The emotion paradox in the aging brain. Annals of the New York Academy of Sciences 1251, 3349.CrossRefGoogle Scholar
Nock, MK, Borges, G, Bromet, EJ, Cha, CB, Kessler, RC and Lee, S (2008) Suicide and suicidal behavior. Epidemiologic Reviews 30, 133154.CrossRefGoogle Scholar
Ormel, J, Riese, H and Rosmalen, JG (2012) Interpreting neuroticism scores across the adult life course: immutable or experience-dependent set points of negative affect? Clinical Psychology Review 32, 7179.CrossRefGoogle Scholar
Osler, M, Andersen, AN and Nordentoft, M (2008) Impaired childhood development and suicidal behaviour in a cohort of Danish men born in 1953. Journal of Epidemiology and Community Health 62, 2328.CrossRefGoogle Scholar
Plomin, R and Deary, IJ (2015) Genetics and intelligence differences: five special findings. Molecular Psychiatry 20, 98108.CrossRefGoogle Scholar
Potijk, MR, Janszky, I, Reijneveld, SA and Falkstedt, D (2016) Risk of coronary heart disease in men with poor emotional control: a prospective study. Psychosomatic Medicine 78, 6067.CrossRefGoogle Scholar
Roberts, BW and DelVecchio, WF (2000) The rank-order consistency of personality traits from childhood to old age: a quantitative review of longitudinal studies. Psychological Bulletin 126, 3.CrossRefGoogle Scholar
Roberts, BW, Walton, KE and Viechtbauer, W (2006) Patterns of mean-level change in personality traits across the life course: a meta-analysis of longitudinal studies. Psychological Bulletin 132, 1.CrossRefGoogle Scholar
Roberts, BW, Kuncel, NR, Shiner, R, Caspi, A and Goldberg, LR (2007) The power of personality: the comparative validity of personality traits, socioeconomic status, and cognitive ability for predicting important life outcomes. Perspectives on Psychological Science 2, 313345.CrossRefGoogle Scholar
Ross, A (1988) De värnpliktigas prestationsförmåga vid inskrivningspövningar i Sverige 1969–1979 [The conscripts' capacity at enlistment testing in Sweden 1969–1979]. Umeå: Umeå Universitet, Pedagogiska Institutionen.Google Scholar
Sörberg, A, Allebeck, P, Melin, B, Gunnell, D and Hemmingsson, T (2013) Cognitive ability in early adulthood is associated with later suicide and suicide attempt: the role of risk factors over the life course. Psychological Medicine 43, 4960.CrossRefGoogle Scholar
Sörberg Wallin, A (2015) The Association of Intelligence with Morbidity, Mortality and Disability Pension: Epidemiological Studies in a Cohort of Swedish men. Stockholm: Institute of Environmental Medicine.Google Scholar
Sörberg Wallin, A, Allebeck, P, Gustafsson, J-E and Hemmingsson, T (2018a) Childhood IQ and mortality during 53 years’ follow-up of Swedish men and women. Journal of Epidemiology and Community Health 72, 926932.CrossRefGoogle Scholar
Sörberg Wallin, A, Zeebari, Z, Lager, A, Gunnell, D, Allebeck, P and Falkstedt, D (2018b) Suicide attempt predicted by academic performance and childhood IQ: a cohort study of 26 000 children. Acta Psychiatrica Scandinavica 137, 277286.CrossRefGoogle Scholar
Stenbacka, M and Jokinen, J (2015) Violent and non-violent methods of attempted and completed suicide in Swedish young men: the role of early risk factors. BMC Psychiatry 15, 196.CrossRefGoogle Scholar
Stone, AA, Schwartz, JE, Broderick, JE and Deaton, A (2010) A snapshot of the age distribution of psychological well-being in the United States. Proceedings of the National Academy of Sciences 107, 99859990.10.1073/pnas.1003744107CrossRefGoogle Scholar
Tang, TZ, DeRubeis, RJ, Hollon, SD, Amsterdam, J, Shelton, R and Schalet, B (2009) Personality change during depression treatment: a placebo-controlled trial. Archives of General Psychiatry 66, 13221330.CrossRefGoogle Scholar
Wiktorsson, S, Berg, AI, Billstedt, E, Duberstein, PR, Marlow, T, Skoog, I and Waern, M (2013) Neuroticism and extroversion in suicide attempters aged 75 and above and a general population comparison group. Aging & Mental Health 17, 479488.CrossRefGoogle Scholar
World Health Organization (2012) Public health action for the prevention of suicide: a framework. Geneva, Switzerland: WHO Document Production Services.Google Scholar
Figure 0

Table 1. Associations of intelligence (IQ) and emotional control (EC) in 1969/1970 with suicidal behavior 1973–2008

Figure 1

Fig. 1. Associations between suicidal behavior and intelligence and emotional control, respectively, with adjustment for each other and for childhood SES. ORs with 95% CIs for suicidal behavior are given for a one step decrease on the five-level scales of intelligence and emotional control for the separate follow-up periods. The time periods end at about 10, 20, 30 and 40 years after conscription, respectively, and correspond with approximate age intervals of 22–28 years, 29–38 years, 39–48 years and 49–58 years.

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