A new study has found that mass shootings and deaths by suicide in the United States share seasonal patterns, reaching their highest levels during summer months.
Analyzing national data spanning 2014 to 2021, researchers observed consistent summertime peaks in both mass shootings and suicide deaths, suggesting that common environmental, behavioral, or biological factors may contribute to seasonal fluctuations in these forms of violence.
While the causes of mass shootings and suicidality are complex and multifactorial, the findings raise the possibility that mass shootings may share risk pathways with suicidal behavior. Prior research has shown that a substantial portion of individuals who perpetrate mass shootings exhibit suicidal thoughts, prior suicide attempts, or an expectation of dying during the attack. The new findings add a population-level perspective, demonstrating that mass shootings and suicides follow similar seasonal rhythms.
The study builds on decades of research demonstrating seasonal variation in suicide, which typically peaks in late spring and summer despite common assumptions that risk is highest during winter months, when symptoms of depression peak in severity. The authors propose several potential contributing factors and emphasize that the findings identify an association rather than a causal mechanism. Further research is needed to determine whether seasonal factors directly influence the risk of mass shootings, and whether prevention strategies developed for suicidality extend to identifying individuals at risk for extreme acts of violence.
The researchers hope that a better understanding of when and why these events occur may ultimately inform efforts to prevent and respond to mass violence and suicidal behavior.
This article, “Seasonality of Mass Shooting Events and Deaths by Suicide in the United States, 2014 to 2021,” by Mark Czeisler, MD, PhD of the Department of Medicine at Brigham and Women’s Hospital and Charles Czeisler, PhD, MD of the Division of Sleep and Circadian Medicine at Mass General Brigham and published in Journal of Biological Rhythms , is free to access and can be read here .
Journal of Biological Rhythms is the official journal of the Society for Research on Biological Rhythms and offers peer-reviewed original research in all aspects of biological rhythms.
If you or someone you know may be considering suicide or experiencing a mental health crisis, call or text 988 to reach the Suicide & Crisis Lifeline, available 24/7 throughout the United States. If there is an immediate risk of harm, call 911 or seek emergency medical care.
Journal of Biological Rhythms
Data/statistical analysis
Not applicable
Seasonality of Mass Shooting Events and Deaths by Suicide in the United States, 2014 to 2021
24-Jul-2026
The authors have no conflicts to declare.