Megan Brooks

June 02, 2014

MINNEAPOLIS — Contrary to common belief, people are more likely to commit suicide in the overnight hours than during the daytime or evening, a new study finds.

"When evaluated across the 24-hour day, and accounting for the proportion of the population likely to be awake, completed suicides are far more likely to occur at night (between midnight and 4:00 a.m.)," Michael Perlis, PhD, associate professor, Department of Psychiatry, and director of the Penn Behavioral Sleep Medicine Program at the University of Pennsylvania in Philadelphia, told Medscape Medical News.

He said the finding helps explain why sleep disturbance has consistently been found to be a risk factor for suicidal ideation and behavior.

"Having insomnia and nightmares (apart from fomenting despair) increases the likelihood that the individual will be awake during a vulnerable time. Second, and more important, it suggests that interventions for insomnia and nightmares may serve to reduce the risk for suicidal ideation and behavior," Dr. Perlis said.

He will present the study here June 3 at SLEEP 2014, the 28th annual meeting of the Associated Professional Sleep Societies.

Dr. Michael Perlis

The study involved archival analyses of both the National Violent Death Reporting System, which provided data for the estimated time of fatal injury, and the American Time Use Survey, which provided an hourly proportion of the US population that is awake.

Time of fatal injury was grouped into 1-hour slots, and the hourly distribution of these data were weighted by the proportion of people awake at each hour and scaled to 100%. A total of 35,332 suicides were included in the analysis.

The results showed that the weighted, scaled mean suicide rate per hour was 10.27% after midnight, peaking at 16.27% between 2:00 a.m. and 11:59 p.m. When 6-hour time blocks were examined, the observed frequency of suicide between midnight and 5:59 a.m. was 3.6 times higher than expected.

Catastrophic Thinking, Low Impulse Control?

"The finding was what we expected — but it was not easily found," Dr. Perlis said.

"On the one hand, it makes all the sense in the world that completed suicides would occur more frequently at night. Partly because of the absence of social constraints, the absence of social supports, the despair of sleeplessness, and easier access to alcohol, substances, and weapons," Dr. Perlis explained. "Partly because it is likely that being awake at night, when one is biologically prepared to be asleep, may be a risk factor in and of itself. The risk being that at this phase of the 24-hour day we all may be particularly vulnerable to catastrophic thinking and low impulse control."

Dr. Perlis said a "first pass" at the data showed what other researchers have found — the frequency of completed suicide rises across the morning hours, peaks in the afternoon, and trends downward to the lowest levels during the midnight to 4:00 a.m. hours.

"It took an epiphanous moment to realize that one cannot simply array the data as we did (percentage per hour). One has to account for the obvious: the odds of being awake at each hour are not the same from one hour to the next. Once we accounted for this factor in the analysis, it became obvious that completed suicide occurs disproportionately at night," he explained.

"The researchers took a very clever and unique approach to study this and demonstrate that suicide is more common at night in an objective way," Clete Kushida, MD, PhD, professor and medical director of the Stanford Sleep Medicine Center in Palo Alto, California, and past president of the American Academy of Sleep Medicine, told Medscape Medical News.

Dr. Kushida, who wasn't involved in the study, said he wasn't particularly surprised by the finding. "There does appear to be some dip in mood that occurs around sleep," he noted.

Dr. Perlis said the findings suggest that circadian factors may contribute to suicidality and help explain why insomnia is also a risk factor for suicidal thoughts and behavior.

He noted that in one of the most vulnerable populations for suicide, returning soldiers and veterans, efforts are "well underway" in the Veterans Affairs (VA) system to get the best insomnia and nightmare treatments to these individuals. System-wide training in cognitive-behavioral therapy for insomnia and nightmares started about 4 years ago in the VA, he said.

The authors and Dr. Kushida have disclosed no relevant financial relationships.

SLEEP 2014: 28th Annual Meeting of the Associated Professional Sleep Societies. Oral Presentation 0768. To be presented June 3, 2014.  


Comments on Medscape are moderated and should be professional in tone and on topic. You must declare any conflicts of interest related to your comments and responses. Please see our Commenting Guide for further information. We reserve the right to remove posts at our sole discretion.