Everybody knows people can feel sluggish, maybe even grouchy, when they don’t get enough sleep.

According to new research published in the journal PLOS Biology, people can also become selfish and less likely to help another person when they don’t get enough sleep.

Researchers from the University of California, Berkeley, conducted three sleep studies. They looked at changes in brain activity and behavior benefiting other people. They found a significant drop after the loss of even a small amount of sleep.

"Even just an hour of sleep loss was more than enough to influence the choice to help another," Ben Simon, a postdoctoral fellow of psychology at the University’s Center for Human Sleep Science, told CNN. "When people lose one hour of sleep, there's a clear hit on our innate human kindness and our motivation to help other people in need."

In one study, charitable donations fell 10% after Daylight Savings Time. In another, there was less activity in the part of the brain associated with considering other people’s needs following sleep deprivation. And in the third study of more than 100 people, researchers found that quality of sleep was more important than quantity, when measuring the effects on selfishness.

"Sleep has been consistently shown to affect our mood and our cognitive functioning, and thus, it also likely affects how we relate to others," said Ivana Rosenzweig, MD, a sleep physician and consultant neuropsychiatrist at Guy's and St Thomas' Hospital in the United Kingdom, who was not involved in the study.

"These findings could suggest that once sleep duration rises above some basic nominal amount, then it appears to be the quality of that sleep that is most critical for aiding and supporting our desire to help other people,” she said.

PLOS Biology: “Sleep loss leads to the withdrawal of human helping across individuals, groups, and large-scale societies.”

CNN: “Not getting enough sleep? It could be making you more selfish.”

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