In recent years, there has been a growing interest in understanding the relationship between sleep and suicide. Although sleep disturbances are commonly cited as critical risk factors for suicidal thoughts and behaviours, it is unclear to what degree sleep disturbances confer risk for suicide. The aim of this meta-analysis was to clarify the extent to which sleep disturbances serve as risk factors (i.e., longitudinal correlates) for suicidal thoughts and behaviours. Our analyses included 156 total effects drawn from 42 studies published between 1982 and 2019. We used a random effects model to analyse the overall effects of sleep disturbances on suicidal ideation, attempts, and death. We additionally explored potential moderators of these associations. Our results indicated that sleep disturbances are statistically significant, yet weak, risk factors for suicidal thoughts and behaviours. The strongest associations were found for insomnia, which significantly predicted suicide ideation (OR 2.10 [95% CI 1.83–2.41]), and nightmares, which significantly predicted suicide attempt (OR 1.81 [95% CI 1.12–2.92]). Given the low base rate of suicidal behaviours, our findings raise questions about the practicality of relying on sleep disturbances as warning signs for imminent suicide risk. Future research is necessary to uncover the causal mechanisms underlying the relationship between sleep disturbances and suicide.

Capability-based models propose that people die by suicide because they want to, and they can. Despite the intuitive appeal of this hypothesis, longitudinal evidence testing its predictive validity has been limited. This study tested the predictive validity of the desire-capability hypothesis. A total of 1,020 selfinjuring and/or suicidal adults were recruited worldwide online from suicide, self-injury, and mental health web forums. After baseline assessment, participants completed follow-up assessments at 3, 14, and 28 days after baseline. Participant retention was high (.90%) across all follow-up assessments. Analyses examined the effect of the statistical interaction between suicidal desire and indices of capability for suicide on future nonfatal suicide attempts. Main analyses focused on the fearlessness about death facet of capability for suicide; exploratory analyses examined preparations for suicide. Logistic regression was used to predict suicide attempt status at follow-up; zero-inflated negative binomial models were implemented to predict the frequency of nonfatal suicide attempts at follow-up. Results were consistent across models, finding very little evidence of the desire-capability interaction as a significant predictor of suicide attempt status or frequency at follow-up. We close with a discussion of the limitations of this study as well as the implications of our findings for future suicide science. General Scientific SummaryCapability-based models of suicide propose that people attempt suicide because they have both the desire and capacity to engage in suicidal behavior. The results of this study failed to support this hypothesis, finding no significant interaction between suicidal desire and fearlessness about death or preparations for suicide. Taken together, this indicates that these factors may at best represent insufficient explanations for why people attempt suicide.

Despite the prominence of the capability-for-suicide construct in suicide research, fundamental hypotheses about its nature and development remain largely untested. In this study, we tested the primary mechanism proposed to account for its development: habituation to painful or provocative events. More than a thousand adults were recruited worldwide from online suicide, self-injury, and mental health web forums and subsequently followed for 28 days. Analyses examined the experiences purported to have the strongest effects: suicidal and nonsuicidal-self-injurious behaviors. Capability was measured explicitly and implicitly. Multiple mediation was used to test whether changes in capability between baseline and 28-day follow-up were accounted for by exposure to self-injurious behaviors that occurred over the intervening time interval. Results failed to support the habituation hypothesis, at least as studied within the methodological constraints of this study. Post hoc power analyses indicated ample power to detect small effects. Results raise questions about the validity of the habituation hypothesis.

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