Could your anger be linked to lack of sleep?
New US research has found that even missing out on just a couple of hours sleep a night could make you angrier and diminish your ability to adapt to certain situations.
Carried out by researchers at Iowa State University, the new study looked at 142 participants who were randomly assigned to two groups.
One group was asked to maintain their normal sleep routine for a period of two days, while the other was asked to restrict their sleep by two to four hours each night for two nights.
Participants also rated their feelings of anger before and after sleep during a test in the lab, in which they were asked to rate products while listening to different background noises, designed to create frustrating situations which could provoke anger.
The findings, published in the Journal of Experimental Psychology: General, showed that those who maintained their regular sleep pattern got on average almost seven hours of sleep a night, while those in the restricted group got about four and a half hours each night, which the researchers say reflects the amount of sleep loss we regularly experience in everyday life.
In addition, the researchers also found that sleep restriction universally intensified feelings of anger, with co-author Zlatan Krizan adding that sleep loss was found to uniquely impact anger, rather than simply resulting from feeling more negative in that moment.
The study is one of the first to provide evidence that a lack of sleep can spark feelings of anger, with previous research finding a connection but not showing a causal relationship according to the researchers. Sleep loss has also been linked to an increase in negative emotions, such as anxiety and sadness, and a decrease in positive emotions, such as happiness and enthusiasm.
"In general, anger was substantially higher for those who were sleep restricted," Krizan said. "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."
"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."
Preliminary results from a separate study by the team also suggest that the experiments in the lab could also apply to real life, with the researchers finding that college students participating in the research also consistently report more anger than usual on the days when they are more sleep deprived.
The researchers are now beginning to collect data to see if sleep loss could even cause aggressive behaviour toward others.