"I love sleep. My life has the tendency to fall apart when I'm awake, you know?" —Ernest Hemingway

Everybody enjoys a good night's sleep, which serves essential functions such as purging the brain's toxins, promoting rest and regeneration, and even helping the brain encode new memories

wavebreakmedia/Shutterstock
Source: wavebreakmedia/Shutterstock

For people who don't get the recommended amount of sleep—seven to nine hours each night for adults—the consequences can be severe. We all suffer from the occasional bout of insomnia, but research on total sleep deprivation shows that sleep debt leads to impaired judgment, loss of emotional control, reduced mental flexibility, and (at least in some cases), psychotic symptoms. Around 33 percent of Americans report loss of sleep for various reasons, so it's hardly surprising that sleep deprivation has been linked to industrial and automobile accidents, as well as judgment errors in almost any task you can name. And it's linked to a wide range of mental health problems, including depression and anxiety.

Is lack of sleep also linked to aggression? 

There is no question that aggressive behavior is distressingly common; in 2012, there were almost 7 million reports of violent victimization. But not all aggressive behavior leads to criminal charges. In most cases, episodes of verbal assault, cyberbullying, and road rage go unreported, but they of course still have a negative impact on how people live their lives. Understanding why people act aggressively, and finding ways to prevent the behavior, motivates researchers and lawmakers alike.

A new article in the journal Psychology of Violence suggests that sleep problems play a far greater role in aggression than researchers suspected. Authors Zlatan Krizan and Anne Herlache of Iowa State University point out the different ways that poor sleep can help release aggressive impulses and fuel violence. Along with case studies showing that violent offenders become less aggressive after being treated for sleep problems, brain research indicates that poor sleep can influence our ability to control impulsive behavior; it also appears connected to how we emotionally respond to threats. 

Though animal research has shown increased aggression in rats following REM sleep deprivation, little research has found similar results in humans. Still, as Krizan and Herlache point out, poor sleep can amplify aggressive tendencies in humans in different ways. First, lack of sleep generally increases negative emotions such as fatigue, anxiety, and depression—other research shows that anger and irritability can increase as well. But poor sleep can also lead to greater physical discomfort and pain, including headaches, stomach aches, and flu-like symptoms. As sleep debt increases, we also become more sensitive to pain and emotional triggers that make us more likely to respond aggressively.

Along with the emotional difficulties linked to poor sleep, cognitive problems are common as well. Lack of sleep leads to impaired judgment and impaired ability to make decisions, especially under pressure. We can also become more paranoid and less flexible in how we respond to frustration or to provoking comments. We might ordinarily be able to handle these situations without problems, but a crushing sleep debt generally means we are more likely to lash out aggressively. It probably doesn't help that a lack of sleep also means we become less inhibited and less likely to control what we may see or do when we become annoyed. While sleep can make us more aggressive, Krizan and Herlache suggest that the link can go both ways: Becoming angry or upset generally increases physiological arousal, making us more likely to spend our time ruminating on the things that bother us, which can undermine our ability to sleep. 

To highlight the link between poor sleep and aggression, Krizan and Herlache examined recent research looking at intimate partner violence, bullying in children and adolescents, and aggressive behavior in psychiatric hospitals and prisons. As expected, the research showed a consistent link between poor sleep and aggressive behavior in all three areas. These findings demonstrate the importance of understanding how sleep problems can influence the way that people think and act, not just in terms of aggression, but all kinds of problem social behavior.

More research on this subject is needed, but we can already appreciate that sleep problems can play an essential role in mental and physical health, not to mention the role it seems to play in aggression and violence. Completely eliminating sleep debt may be impossible for many people, but treating ongoing sleep problems can yield results we are just beginning to appreciate.

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