We all get cranky after a poor night’s sleep. Some of us even experience digestive issues, cravings, and weakened immunity. Sleep regulates everything from our mood to our appetite, our ability to heal and manage our weight. Now, new research suggests that lack of sleep may also contribute to selfish behavior.

At the University of California, Berkeley, researchers performed three studies examining the phenomenon. They discovered that most people did not want to help others after a bad night’s sleep, even if the sleep loss was minimal.

Ben Simon, a postdoctoral fellow of psychology at the Center for Human Sleep Science said about the findings: “Even just an hour of sleep loss was more than enough to influence the choice to help others.”

There were three studies in total. For the first, researchers reviewed a database of 3 million charitable donations that took place between 2001 and 2016. Just after Daylight Savings Time, donations dropped by 10%, yet this drop only happened in states that observe Daylight Saving Time.

Researchers did a second study in which they used imaging to record brain activity in people after eight hours of sleep vs. no hours of sleep. The part of the brain that controls theory of mind (the ability to consider the needs of others, as well as other’s emotions) was less active in those right after sleep deprivation.

For the third study, over 100 participants were monitored over the course of 3-4 nights. The data showed that over the course of these 3-4 nights, the quality of sleep mattered more than quantity as it relates more or less to selfishness.

What these studies suggest is that lack of sleep and good sleep quality has impacts far beyond the individual. Sleep is necessary for “balanced social and cognitive functioning, including altruism.”