Suicides are much more likely to happen between midnight and 4 a.m. than during the daytime or evening, according to a new study. New evidence suggests that circadian factors may be a contributing factor to suicide.

According to study results, the weighted, scaled mean suicide rate per hour was 10.27 percent past midnight, with a peak of 16.27 percent between 2 a.m. and 2:59 a.m. The mean suicide rate per hour was 2.13 percent between 6 a.m. and 11:59 p.m. When six-hour time blocks were examined, the observed suicide frequency between midnight and 5:59 a.m. was 3.6 times higher than previously expected.

Michael Perlis, principal investigator, PhD, associate professor in the Department of Psychiatry and Director of the Penn Behavioral Sleep Medicine Program at the University of Pennsylvania in Philadelphia, said in a statement, “This appears to be the first data to suggest that circadian factors may contribute to suicidality and help explain why insomnia is also a risk factor for suicidal ideation and behavior.” He continued, “These results suggest that not only are nightmares and insomnia significant risk factors for suicidal ideation and behavior, but just being awake at night may in and of itself be a risk factor for suicide.”

According to Psychology Today, circadian rhythm is “a 24-hour cycle that tells our bodies when to sleep and regulates many other physiological processes.” The source notes, “When one’s circadian rhythm is disrupted, sleeping and eating patterns can run amok. A growing body of research is examining the adverse health effects a disrupted circadian rhythm can have, like increasing the chances of cardiovascular events, obesity, and a correlation with neurological problems like depression and bipolar disorder.”