Suicidal behaviour
The rates of suicidal thoughts and behaviour in Ten to Men adult respondents are higher than reported in the 2007 National Survey of Mental Health and Wellbeing (NSMHWB), the benchmark population data collection on non-fatal suicidal thoughts and behaviours in adults in Australia. Lifetime suicidal ideation was reported by 18.8 % of Ten to Men adult respondents compared to 11.5 % of males in the NSMHWB, and lifetime suicide attempts were reported at more than twice the rate in Ten to Men adult respondents (5.4 % compared to 2.2 %) [14]. Likewise lifetime and 12 month depression was reported more frequently in the Ten to Men adult cohort (depression: 20 % lifetime and 12.8 % 12 month) than in the NSMHWB (depressive episode: 8.8 % lifetime and 3.1 % 12 month) [14], although anxiety was less frequently reported (Ten to Men: 13.4 % lifetime and 8.8 % 12 month; NSMHWB: 20.4 % lifetime and 10.8 % 12 month) [14]. These differences in rates likely reflect methodological differences including the use of self-report questionnaires in Ten to Men versus face-to-face interview in the NSMHWB and the use of clinical interview to assess depression and anxiety in the NSHWBS compared to a general question about lifetime diagnosis in Ten to Men. While the study design aimed to obtain a representative sample and sample weights adjusting for age and region have been applied to the analysis [13], Ten to Men is not designed as a cross-sectional prevalence study but rather a longitudinal study aimed at investigating the causes of and pathways to health outcomes within individuals. As such, a cohort enriched for suicidal behaviour and psychiatric disorder offers greater scope to investigate the complex causality of suicidal behaviour.
Life stress and suicidal ideation
In the initial multivariable analysis, elements from both the stressor and diathesis domains increased risk for suicidal ideation. Depression, anxiety and alcohol use, all putative elements of the diathesis for suicidal behaviour, were associated with increased risk for suicidal ideation. Depression in the past 12 months was the most robust predictor with more than twice the effect size of any other risk factor in the model. In the stressor domain six of the twenty-four life events assessed made an independent contribution to risk for suicide ideation. While a smaller effect than depression, these life events contributed to risk in the same magnitude as anxiety and harmful/hazardous alcohol use, suggesting that the stressor domain has an important role and is thus a potential target for intervention in suicide prevention.
The six life events associated with increased odds of suicidal ideation were serious family conflict, break-up of a relationship, difficulty finding a job, legal troubles, major loss of property and serious personal injury. Of these, events in the employment and interpersonal domains had somewhat stronger effects. Liu and Miller in their recent systematic review found some evidence that relative to other types of stressors interpersonal difficulties were more often associated with suicidal thoughts although they did not present data specific to males [5]. In this study, the variable nature of the six significant life events and the modest differences in effect sizes between them makes it difficult to identify particular domains or types of life events that are higher risk than others. Moreover, while certain life events were found to be more strongly associated with increased risk for suicidal thoughts than others, the likely collinearity between life events and the low frequencies of certain events (e.g., loss of a child) may have meant that events which are highly stressful were not retained in the final models. Thus no general conclusions can be drawn about the salience of particular life events over others with respect to risk for suicidal thinking. The variability may also indicate that the type of life event is less important to risk for suicidal ideation than the broader context in which any particular life event takes place, including the presence of elements of the diathesis.
While we cannot elucidate causal pathways in a single wave of data, we can investigate if the co-occurrence of a stressor and elements of the diathesis increases risk for suicidal behaviour. In the case of depression, we found this to be the case. The co-occurrence of life events and depression in the past 12 months resulted in an almost four-fold increase in risk for suicidal ideation over life events with no co-occurring depression, as well as a 35 % increase in the odds of suicidal ideation compared to depression in the absence of life events. While this elevated risk for suicidal ideation associated with co-occurring stressors and depression is consistent with a stress-diathesis model, our analysis also indicates that life events plus depression does not fully encapsulate the stress-diathesis pathway. Independent effects for both life stress and depression persisted in the model and, moreover, the magnitude of increase in ORs associated with co-occurring life stressors and depression did not demonstrate the multiplicative relationship as might be expected if life events plus depression alone constituted the stress-diathesis pathway.
The independent risk associated with life events, depression and, to a lesser degree, anxiety and alcohol use, likely reflects the multi-dimensional nature of both the stressor and diathesis domains. Thus, in the absence of depression other diathesis elements such as deficits in cognitive function, maladaptive stress response, aggression, impulsivity etc. not included in this analysis may be pathways to suicidal ideation in response to life stressors. Likewise, in the stressor domain we assessed only a limited range of life events on the more severe end of the spectrum, and among those in the ‘depression alone’ group reporting suicidal thoughts other life stressors may be occurring. Given the multi-determined nature of suicidal ideation and behaviours it is also likely that there are multiple phenotypes and causal pathways. More complex modelling that includes a broader range of stress and predisposing factors is required to elucidate these. However, this limited analysis of more commonly occurring stressors and psychiatric disorders does indicate that the co-occurrence of life stress and depression substantially increases the risk of suicidal ideation. It also indicates a need for further research to identify predisposing factors in non-depressed males which may increase their vulnerability to suicidal ideation and behaviour when encountering fairly common life stressors in order to identify targets for prevention in this group.
Limitations
The outcome measure of suicidal ideation was drawn from a composite scale designed to assess depression rather than from a suicide assessment instrument and, as such, may lack specificity. Moreover, given that suicidal ideation is a symptom of depression, individuals who were positive for current depression were more likely to have endorsed current suicidal ideation and 12 month depression. While this may overestimate the magnitude of the association between depression and suicidal ideation, the finding that several life events remained significantly associated with suicidal ideation after controlling for depression indicates the robustness of that association. Other limitations are those found in life event studies using self-report checklists regarding reliability of recall of past life events [15]. While the relatively short recall period (past 12 months) and the serious nature of the life events assessed may reduce recall error in Ten to Men this remains a limitation of the checklist method for capturing life event information. Moreover, as with all cross-sectional studies a single wave of data can only discern correlations. Thus we cannot rule out reverse causality whereby individuals who are currently depressed and suicidal may differentially recall more adverse events compared to those who are not, as has been reported in some studies, but not all [16, 17]. Finally, this study does not include any assessment of early-life stressors. Early life trauma has been associated with suicidal behaviour [18] and a number of putative pathways implicated including neurodevelopmental deficits resulting in impaired stress response later in life and greater vulnerability to psychiatric disorder [19]. This study focussed on proximal life stressors (past 12 months) as putative ‘triggers’ to current suicidal ideation, however it is likely that for some individuals early-life stressors contribute to the association between suicidal thoughts and life events observed here, and that analyses examining both distal and proximal stressors are required to fully elucidate the relationship between life stress and suicidal ideation. Over its longitudinal course, Ten to Men will be better able to track the timing of life stressors and identify causal pathways between proximal and distal life events, psychiatric illness and suicidal behaviour.