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Why poor sleep leads to aggressive behavior

image of angry man

Why poor sleep leads to aggressive behavior

Dr. Anthony Warren
| 2023-02-07 | 3 min read

Nearly every day we wake up to learn about some new horrendous violent event. At the same time, according to a recent study by the National Sleep Foundation, a full 45% of adults in the US are only getting 80% of needed sleep. Are these two situations related?

In fact, a growing body of research suggests that lack of sleep may play a role in the perpetration of violence. Studies have shown that people who regularly get less than 6.5 hours of sleep per night are more likely to engage in physically aggressive behaviors, such as domestic violence, workplace bullying and, yes, road-rage.

Recent research at Southwest University, in Chonguin, China sought to uncover the causal relationship and mechanisms for these observations. 450 students aged between 16-26 years were monitored at a two-year interval. Each time the students’ sleep quality was assessed together with a measure of aggression rated for each of the standard sub-categories: hostility, physical aggression, impulsiveness and anger. There was a strong correlation between sleep quality at Time 1 affecting aggressiveness at Time 2. Surprisingly, out of the four categories, only hostility increased significantly when sleep was deprived. And the opposite effect, namely poor sleep resulting from aggressiveness was not observed; aggressive individuals appear to have no problems with sleeping well!

In order to shine some light on these rather unexpected findings the students also underwent functional magnetic resonance imaging (fMRI) to measure brain activity. The scans revealed that poorer sleep quality and increased aggression were tied to reduced activity in certain brain areas, namely in the limbic or frontal regions. These can lead to a lowered ability to correctly interpret the emotions of others. At the same time activity in the left and right dorsolateral prefrontal cortex increased, indicating potential emotional over-reaction to a perceived threat.

Combining these two changes in brain activity suggests poor sleep first lowers the ability to read a potential confrontation, and then stimulates over-reaction to the perceived threat with aggressive behavior.

Indeed, prolonged sleep deprivation may cause permanent changes to the brain through the mechanism of neuroplasticity gradually morphing a once calm person into an irritable, touchy individual ready to turn aggressive at any slight provocation.

Other research has determined that in many developed societies the stressful pace of life has led to a so-called ‘sleepdemic’. The US Sleep Foundation for example has reported that 45% of respondents to a large survey of adults are not getting their needed sleep during the week with an average of just six and a half hours nightly, about 20% below the recommendations. On non-workdays this rose to over 71% but with the average at least going up to seven hours and twelve minutes which however is still about 10% below the target.

Given the clear link between lack of sleep and violence, it is important that we take steps to ensure we are getting enough sleep each night. This means making sleep a priority, creating a sleep-conducive environment, and avoiding things that can disrupt our sleep, such as caffeine, alcohol, and electronic devices.

In conclusion, the relationship between lack of sleep and violence is a complex and multi-faceted one. However, the evidence clearly suggests that adequate sleep is crucial in helping to prevent aggressive behaviors and promoting more peaceful homes and workplaces as well as a harmonious society. Perhaps if we could all sleep a little better, we could wake-up to less depressing headlines!


Kamphuis J., Lancel M, The Interrelations Between Sleep, Anger, and Loss of Aggression Control, (2015), Sleep and Affect, Academic Press, pp. 247-271 Editor(s): Kimberly A. Babson, Matthew T. Feldner

Krizan, Z., & Hisler, G. (2019). Sleepy anger: Restricted sleep amplifies angry feelings. Journal of Experimental Psychology: General, 148(7), 1239–1250.

Haobo Zhang and Xu Lei. (2023). Effect of subjective sleep quality on aggression: A two-year longitudinal and fMRI pilot study. Biological Psychology, Vol. 176, 108454

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