Researchers reveal that suicide and homicide risks peak at night due to factors like disrupted sleep and alcohol, suggesting a link between nocturnal wakefulness and impulsive violence. Credit: SciTechDaily.com

An analysis of 15 years of national data on suicides and homicides shows that nocturnal wakefulness is associated with death by both suicide and homicide, possibly driven by deficits in behavioral and emotional regulation.

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. This is according to a new analysis by researchers in the Department of Psychiatry at the University of Arizona College of Medicine – Tucson.

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

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 five-fold greater risk for suicide and an eight-fold 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 today (May 29) in Journal of Clinical Psychiatry.

“The fact that these overnight risk patterns apply to both suicide and homicide are 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.”

Michael Grandner, PhD, is an associate professor of psychiatry, director of the Behavioral Sleep Medicine Clinic and a BIO5 Institute member. Credit: University of Arizona College of Medicine – Tucson

The ‘Mind After Midnight’ Hypothesis

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, conflict, but not among those who used cannabis or were currently
depressed.

Individuals aged 15-24 years experienced a three-fold 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.”

Reference: “Risk for Suicide and Homicide Peaks at Night: Findings From the National Violent Death Reporting System, 35 States, 2003–2017” 29 May 2024, Journal of Clinical Psychiatry.
DOI: 10.4088/JCP.23m15207