The mind after midnight: Study shows disrupted sleep increases risk for suicide and homicide

May 29, 2024

Nocturnal wakefulness is associated with death by both suicide and homicide, possibly driven by deficits in behavioral and emotional regulation.

person sitting on edge of bed at night, unable to sleep

Researchers conducted an analysis of 15 years of national data on suicides and homicides and found that nocturnal wakefulness could be a contributing factor in both.

portrait of psychiatrist and sleep researcher Andrew Tubbs, MD, PhD

Andrew Tubbs, MD, PhD, is a researcher in the Sleep and Health Research Program at the University of Arizona College of Medicine – Tucson’s Department of Psychiatry.

An analysis by researchers in the Department of Psychiatry at the University of Arizona College of Medicine – Tucson showed that risks for death by suicide and homicide peak at night, with nocturnal wakefulness, age, alcohol use and relationship conflicts being especially prevalent as contributing factors.

Nearly 19% of suicides and 36% of homicides occur at night. Suicide and homicide share little in common, but their highly concordant overnight risk patterns suggest a common feature: nocturnal wakefulness.

“Disrupted sleep may acutely impair rational thought, which can drive impulsive behaviors in vulnerable individuals,” said first author Andrew Tubbs, MD, PhD, a researcher in the Sleep and Health Research Program at the UArizona College of Medicine – Tucson’s Department of Psychiatry. “Our analysis of 15 years of data across the U.S. showed that there is a fivefold greater risk for suicide and an eightfold greater risk for homicide between 2 a.m. and 3 a.m. when adjusting for the number of people who are awake and capable of suicide or homicide.”

The paper, “Risk for Suicide and Homicide Peaks at Night: Findings From the National Violent Death Reporting System, 35 States, 2003–2017,” was published May 29 in the Journal of Clinical Psychiatry.

portrait of sleep researcher Michael Grandner, PhD

Michael Grandner, PhD, is the director of the Behavioral Sleep Medicine Clinic and an associate professor of psychiatry in the College of Medicine – Tucson.

“The fact that these overnight risk patterns apply to both suicide and homicide is striking,” said the study’s senior author, Michael Grandner, PhD, an associate professor of psychiatry, director of the Behavioral Sleep Medicine Clinic and a BIO5 Institute member. “In our review of more than 78,000 suicides and 50,000 homicides, we can find some insight into why nocturnal wakefulness – what we are calling ‘the mind after midnight’ – carries a distinct risk for dysregulated behaviors.”

The authors’ “mind after midnight” hypothesis proposes that nocturnal wakefulness deteriorates the brain’s complex decision-making functions and reduces rational thinking during a time when negative mood is at its peak, positive mood is at its lowest, and risk/reward processing is distorted.

The findings supported that hypothesis. Nighttime risk was greater among adolescents and young adults, people who were intoxicated with alcohol, and those experiencing current partner conflict, but not among those who used cannabis or were depressed.

Individuals aged 15-24 experienced a threefold greater nighttime risk for suicide, while there was an unexpected suicide risk among older adults at 6 a.m. Risk for homicide did not vary by age, though young adults accounted for more than half of all homicide victims.

“Few studies have examined time-of-day trends in violent crime,” Tubbs said. “Future studies could clarify what exactly is happening in the brain to predispose people to these sorts of risks and whether evidence-based strategies to improve sleep and reduce nighttime wakefulness can help reduce the risks and prevent these tragic outcomes.”


Jamie Manser
Department of Psychiatry