Why getting just two hours less sleep a night can make you an angrier person

Rosie Fitzmaurice
Photo by Alexandra Gorn on Unsplash

A new study published in the Journal of Experimental Psychology: General has found evidence to suggest that a lack of sleep really does make you an angrier person.

But that’s obvious, right?

Researchers from Iowa State University asked 142 participants to either maintain their normal sleep pattern or restrict it by between two and four hours over the course of two nights. The former got on average almost seven hours of sleep each night, while the latter got about four and a half hours.

The respondents were required to perform tasks – rating products – in a lab before and after their kip while listening to brown noise (which sounds a bit like spraying water) or a more irritating white noise (which sounds like static signal).

The idea was to create an uncomfortable scenario by adding these sounds, which might make people feel angry. And, unsurprisingly, they found that sleep restriction “universally intensified anger."

"In general, anger was substantially higher for those who were sleep restricted," says study co-author Zlatan Krizan, professor of psychology at Iowa State.

"We manipulated how annoying the noise was during the task and as expected, people reported more anger when the noise was more unpleasant. When sleep was restricted, people reported even more anger, regardless of the noise."

The results suggest people are less able to cope with irritating or frustrating situations when they're tired, the authors concluded.

While previous research has found a link between sleep and anger, questions persisted over whether a lack of sleep was the cause, or if anger was to blame for disrupted sleep, says Krizan.

"Despite typical tendencies to get somewhat used to irritating conditions – an uncomfortable shirt or a barking dog – sleep-restricted individuals actually showed a trend toward increased anger and distress, essentially reversing their ability to adapt to frustrating conditions over time. No one has shown this before," Krizan added.

The authors are now working on another study, with a slightly larger sample over a month, to determine whether their findings extend to everyday life.