Turns out you may actually need to cut your tired coworker some slack.
In a peer-reviewed paper published in the journal PLoS Biology, researchers from the University of California, Berkeley, said they had found a potential link between disrupted sleep and selfishness.
Aside from reducing our energy levels, sleep deprivation is also known to trigger physical effects like a reduced attention span, poor decision making, and worsened memory—but according to the Berkeley study, it could also be killing our altruistic tendencies.
The study found that losing just one hour of sleep could be enough to destroy our willingness to help others—even family and close friends.
The research team ran a series of experiments to determine a link between sleep and selfishness.
First, they analyzed people’s behavior after a good night’s sleep and a night’s sleep of deprivation, finding that 78% of participants demonstrated “a reduction in the desire to help others” when they had lost out on sleep.
The effect was consistent among all participants, researchers noted, regardless of their mood, energy levels, or whether they were empathetic individuals.
“The withdrawal of helping caused by sleep loss was significant no matter whether the circumstance involved helping a stranger or helping someone familiar (i.e. friends/colleagues),” they added.
“This would suggest that familiarity with the individual in need of help (e.g., a friend versus stranger) does not appear to confer immunity against the sleep loss-associated reduction in the desire to act altruistically.”
They then carried out brain scans, asked participants to fill in behavior surveys, and monitored changes to charitable donations when Americans lost an hour of sleep in the switch to Daylight Savings Time (DST).
MRI scan analyses found a link between sleep loss and reduced activity in the part of the brain associated with engaging in “prosocial behaviors”—behaviors that benefit other people or society as a whole.
The behavioral surveys, where participants self-reported their sleep duration and next-day behavior, found that worse sleep efficiency was associated with decreases in the desire to help others the following day.
Meanwhile, researchers found that the transition to DST, which meant huge swathes of the U.S. population lost an hour’s sleep, “decreases real-world behavioral acts of altruistic helping at a larger societal level.”
Scientists analyzed more than 3 million charitable donations made between 2001 and 2016 in the U.S. during the transition to DST in the spring of each year in states that observed DST.
“The transition to DST was associated with a significant decrease in the altruistic decision to give away money (make donations) compared to the weeks either before or after the transition,” researchers said.
“Findings across all three studies establish insufficient sleep (both quantity and quality) as a degrading force influencing whether or not humans wish to help each other, and do indeed, choose to help each other,” they added.
“The implications of this effect may be non-trivial when considering the essentiality of human helping in the maintenance of cooperative, civil society, combined with the reported decline in sufficient sleep in many first-world nations.”
Sign up for the Fortune Features email list so you don’t miss our biggest features, exclusive interviews, and investigations.