Nocturnal Wakefulness as a Previously Unrecognized Risk Factor for Suicide.

OBJECTIVE Suicide is a major public health problem and the 10th leading cause of death in the United States. The identification of modifiable risk factors is essential for reducing the prevalence of suicide. Recently, it has been shown that insomnia and nightmares significantly increase the risk for suicidal ideation, attempted suicide, and death by suicide. While both forms of sleep disturbance may independently confer risk, and potentially be modifiable risk factors, it is also possible that simply being awake at night represents a specific vulnerability for suicide. The present analysis evaluates the frequency of completed suicide per hour while taking into account the percentage of individuals awake at each hour. METHODS Archival analyses were conducted estimating the time of fatal injury using the National Violent Death Reporting System for 2003-2010 and the proportion of the American population awake per hour across the 24-hour day using the American Time Use Survey. RESULTS The mean ± SD incident rate from 06:00-23:59 was 2.2% ± 0.7%, while the mean ± SD incident rate from 00:00-05:59 was 10.3% ± 4.9%. The maximum incident rate was from 02:00-02:59 (16.3%). Hour-by-hour observed values differed from those that would be expected by chance (P < .001), and when 6-hour blocks were examined, the observed frequency at night was 3.6 times higher than would be expected by chance (P < .001). CONCLUSIONS Being awake at night confers greater risk for suicide than being awake at other times of the day, suggesting that disturbances of sleep or circadian neurobiology may potentiate suicide risk.