Total sleep time as a predictor of suicidal behaviour.

Insomnia symptoms are a known predictor of suicide; however, less is known about the relationship between hypersomnia and suicide, and how total sleep time may better account for suicidal ideation compared with subjective reports of insomnia symptoms. In the present secondary data analysis, a squared term confirmed the importance of both short and long total sleep time on suicidal behaviour. Total sleep time had a significant positive direct effect on suicidal behaviour (b = 0.20, SE = 0.08, P < 0.05), significant negative direct effects on insomnia symptoms (b = -1.67, SE = 0.13, P < 0.0001) and on depressive symptoms (b = -1.76, SE = 0.29, P < 0.0001). Depression had a significant positive effect on suicidal behaviour (b = 0.17, SE = 0.01, P < 0.0001), and significantly mediated the relationship between total sleep time and suicidal behaviour, but insomnia symptoms did not. Total sleep time squared had a significant positive relationship with suicidal behaviour (b = 0.02, SE = 0.01, P < 0.05), significant negative direct effects on insomnia symptoms (b = -0.12, SE = 0.01, P < 0.0001) and on depressive symptoms (b = -0.12, SE = 0.02, P < 0.0001). Depression had a significant positive effect on suicidal behaviour (b = 0.17, SE = 0.01, P < 0.0001), and significantly mediated the relationship between total sleep time and suicidal behaviour. These results suggest the importance of assessing for total sleep time in clinical settings with regard to suicide risk.