The association between premorbid cognitive ability and social functioning and suicide among young men: A historical-prospective cohort study

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Abstract

Previous studies have found associations between low cognitive ability and later completed suicide. The aim of this study was to examine the association between cognitive ability and social functioning in adolescence, and later completed suicide in a large population-based longitudinal study. Data from the Israeli Draft Board Register for 634,655 Israeli male adolescents aged 16 and 17 was linked to a causes-of-death data registry, with a mean follow-up of 10.6 years for completed suicide. Our results show that in males without a psychiatric diagnosis, both low (adjusted HR=1.51, 95% CI: 1.19–1.92) and high (adjusted HR=1.36, 95% CI: 1.04–1.77) cognitive ability, and very poor (adjusted HR=2.30, 95% CI: 1.34–3.95) and poor (adjusted HR=1.64, 95% CI: 1.34–2.07) social functioning were associated with increased risk for later completed suicide; however positive predictive values were low (PPVs=0.09% and 0.10%, for low cognitive ability and very poor or poor social functioning, respectively). No association between cognitive ability or social functioning and risk for suicide was found in males with a psychiatric diagnosis. These data do not support the clinical utility of screening for such potential predictors.

Introduction

Suicide is the third most common cause of death among adolescents and young adults in Western countries (Haas et al., 2010, Pompili et al., 2010), and is complex outcome of multiple, inter-related genetic and environmental factors (Mann, 2002; Moscicki, 1997). This highlights the importance of attempting to characterize adolescents who later died by suicide; adolescents at high risk for suicide might then be the focus of interventions aimed to decrease risk, and hopefully decrease rates of adolescent suicide.

Studies on the relationship between pre-morbid intelligence and risk for completed suicide have shown both higher (Gunnell et al., 2005, Osler et al., 2008, Sörberg et al., 2013) and lower intelligence (Apter et al., 2008, Voracek, 2013) to be associated with later suicide. In addition, previous research has emphasized the importance of social aspects in understanding suicidal behavior in adolescents, however most of the work done in this context examined suicide attempts or suicidal ideation, and not completed suicides (King and Merchant, 2008). Studies assessing the role of social factors in completed suicides are sparse, and retrospective, were based on psychological autopsies (Manoranjitham et al., 2010, Zhang et al., 2010) or did not include a control group (Heikkinen et al., 1995). A recent longitudinal study on a small study of male adolescents (Buhnick-Atzil et al., 2015) found that those who later died by suicide were described as having more interpersonal difficulties in comparison with matched living controls. Correspondingly, a retrospective study (Zhang et al., 2010) found that having low levels of social support were associated with increased risk of suicide. An additional study (Manoranjitham et al., 2010) found that living by oneself and the ending of a steady relationship within the past year were associated with increased risk of suicide.

To date, there are no reports of a large longitudinal study assessing the association between social functioning and completed suicide in a general population sample. Since suicide is a rare event, studying risk factors for suicide needs large samples, in order to include a significant number of suicides, and therefore it is of extreme importance to utilize large population-based cohorts when possible.

The Israeli military routinely screens all Jewish male adolescents in the population, as part of their assessment for eligibility to serve. Using a historical-prospective design, we utilized data on the pre-induction assessments of almost 1 million Israeli male adolescents, and followed them (mean follow up of 10 years) for suicide using a national registry of causes of death. The aim of this study was to characterize the cognitive and social functioning of adolescents who later died by suicide. As far as we know, this is the first large study to use prospectively collected data to examine the association between social functioning and completed suicide.

Section snippets

Study population

Baseline data was available for 988,847 Israeli male adolescents who were consecutively screened by the Israeli Draft Board. After the exclusion of 351,986 adolescents with missing data on cognitive (n=96,219), social functioning (n=195,253) or SES measures (n=170,427), and the exclusion of 4455 adolescents who had died for reasons other than suicide, the final sample included 634,655 conscripts with complete data (some conscripts had missing data and died for reasons other than suicide). The

Results

Of the 604,657 without psychiatric disorders, 427 (0.07%) died by suicide, while 55/29,998 (0.18%) of those with any psychiatric disorder died by suicide (χ2(1)=47.86, p<0.001), confirming the association between mental illness and suicide in this cohort. The association between mental illness and definite suicide persisted after adjustment for SES and immigration (HR=2.22, 95% CI=1.71–2.87).

Among mentally healthy males, those with low or high cognitive ability were at increased risk for

Discussion

The findings of this study suggest that although high and low cognitive ability and poor social functioning are associated with statistically increased risk for suicide in mentally healthy males, the positive predictive values of these characteristics are very low. Thus, although these factors may be relevant to the challenge of determining suicidal potential, this study does not support their current clinical significance as predictors.

The U-shape relationship we found between cognitive

Role of funding sources

None.

Contributors

Study concept and design– MW, AR, MD, GL.

Data acquisition– EF, GL.

Data analysis– DF, NW, SG, AR.

Interpretation of the data– MW, DF, NW, SG, AR, ML, MD.

Drafted the manuscript– MW, DF, NW, SG, EF, ML.

Revised the manuscript for important intellectual content– AR, SB, ML, MD, GL.

All authors contributed to and have approved the final manuscript.

Conflict of interest

None.

Acknowledgement

None.

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