Nocturnal Wakefulness and Suicide Risk in the Australian Population.

Objective: Temporal patterns for suicide over a 24-hour period have shown mixed results among prior studies. However, analyses of 24-hour temporal patterns for wakeful actions including suicidal behavior should adjust for expected sleep requirements that inherently skew such activities to conventional wakeful times. This study analyzed the time-of-day for suicide cases from the Australian population for the year 2017, adjusting for expected sleep patterns. Identification of time-of-day trends using this methodology may reveal risk factors for suicide and potentially modifiable contributors. Methods: The Australian National Coronial Information System database was accessed, and data for completed suicide were extracted for the most recent completed year (2017). Time of suicide was allocated to one of four 6-hourly time bins across 24 hours, determined from time last seen alive and time found subsequently. Prevalence of suicide for each time bin was adjusted for the likelihood of being awake for each bin according to sleep-wake norms published from a large Australian community survey. Observed prevalence of suicide was compared to expected values predicted from likelihood of being awake across each time bin calculated as a standardized incidence ratio (SIR). Results: For the year 2017, there were 2,808 suicides, of which 1,417 were able to be allocated into one of four 6-hourly time bins. When compared to expected values, suicides were significantly more likely to occur in the overnight bin (2301-0500; SIR = 3.93, P < .001). Conclusions: Higher-than-expected rates of suicide overnight associated with nocturnal wakefulness may represent a modifiable risk factor for triggering suicide events.