Not getting enough sleep is bad for you in many ways. It increases the risk of several serious health problems, from cardiovascular disease to diabetes to depression. But according to a new study, it could also be bad for those around you. According to the study, not getting enough shut-eye could make you significantly less generous.

Bad sleep, bad relationships

Generosity is one of humanity’s most underrated features. In fact, UC Berkeley researchers Eti Ben Simon and Matthew Walker argue that it’s part of what makes us human.

“Humans help each other. Helping is a defining feature of Homo sapiens, and through such cooperative helping, modern civilization has been made possible. But what determines whether individuals, groups, or entire societies decide to help each other, or choose to look away?”

The two scientists have been studying sleep for quite some time, and they suspected sleep has something to do with it. They linked a lack of sleep to loneliness and social withdrawal — and probably everyone has experienced something of this sort. When you’re tired and haven’t slept well, the last thing you want to do is go meet other people. But could there be more to this story, and could sleep actually impact other social behaviors as well?

Previous research has linked lack of sleep to impaired activity in a region within the brain called the social cognition network. This network is important for understanding other people’s emotions and empathizing with them.

“That led us to pose the logical question and hypothesis: if a lack of sleep impairs the activity of the prosoccial brain network, does that result in a withdrawal of our desire to help other people in the world, and can you see this under tight laboratory experiment conditions, AND can you see it played out in the real world, with real-world, global consequences?”

Their new study actually contains three separate studies that assessed how sleep (or lack of sleep) affects people’s willingness to help others. The first one involved 24 healthy volunteers who were placed in an fMRI and had their brains scanned after a night of sleep versus no sleep. The scans showed that indeed, the part of the brain responsible with empathy was less active after less sleep.

The second study involved tracking 100 people online over 3-4 nights. During this time, researchers measured how much these people slept (and how well), and then measured how much they wanted to help others directly (they looked at things like holding an elevator door open for someone else or helping someone on the street). Here too, a connection was observed between a lack of sleep and a lack of generosity.

Lastly, they mined a database of 3 million charitable donations in the US between 2001 and 2016 to see whether the number of donations changed after transitioning to Daylight Saving Time, when people would have one less hour of sleep.

“What we found was overwhelming support for the hypothesis that even surprised us: when you are under-slept, you become more selfish, you withdraw from society, and you choose not to help other people. We replicated this in three independent studies, described in the next response below.”

Remarkably, the researchers found a 10% decrease in donations in parts of the US that kept Daylight Savings — but this dent wasn’t observed in regions that didn’t change their clocks. “This finding was perhaps the most surprising to us,” the researchers note.

No sleep makes people more selfish

“Sleep loss (both total deprivation and even modest night-to-night reductions) leads individuals to withdraw their choice to help others, relative to the very same individuals’ helping desire following a rested night of sleep. This was true even when taking into account the negative impact of sleep loss on mood and motivation,” the researchers tell ZME Science.

Perhaps even more surprising is that when people were sleep-deprived, they were less likely to help others regardless of whether they were close to them (friends or family) or people they didn’t know. Again, it didn’t need to be something extreme — just 1 hour was enough to make a notable difference.

“In this study, we demonstrate that insufficient sleep represents a causal, yet previously unrecognized, factor dictating whether or not humans choose to help each other, triggered by a breakdown in the activity of key prosocial-brain networks.”

The findings show that sleep loss can act as a trigger of asocial behavior, and seems to reduce people’s innate desire to help others. Considering how essential human generosity is for maintaining cooperative and civilized societies (and with the serious erosion of sleep time over the past 50 years), the ramifications of this study are serious. If people are sleeping less, we could see societal breakdowns because of this; donations are one aspect, but there are plenty of more subtle examples. A lack of sleep could even affect the sentiments of entire nations, the researchers note. Furthermore, the results suggest we may need to look at this more closely, especially in communities suffering from worse sleep.

“Considering that more than half of all people in developed countries report getting insufficient sleep during the work week, this proposition may warrant greater investigation at a societal level. If found to be true, it may necessitate methods to enhance sleep awareness and the development of policies that improve sleep opportunities for individuals within affected communities.”

Sleeping is social lubricant

Alcohol is sometimes regarded as a social lubricant, but judging by the results of the study, sleep could be an even better lubricant.

Ironically, sleeping a lot is seen as something that takes away from our rich social lives, but in fact, adequate sleep does the opposite, it helps promote healthy, generous relationships between humans. Promoting sleep, rather than shaming people for sleeping enough, could shape the social bonds we experience on a day to day basis. It could even be a social necessity, given the way modern society is shaping up.

Ultimately, the bottom line is that sleep is severely undervalued at the moment — and we’re paying a heavy price for it. Most if not every disease that’s killing us is linked to cancer — from Alzheimer’s to cancer and stroke to diabetes, they’re all linked to insufficient sleep. Sleep deprivation is making us less healthy, less smart, and as this new work suggests, less willing to conduct an activity that makes us human.

“Sleep is essential for all aspects of our physical, mental, and emotional lives,” Ben Simon said. “When sleep is undervalued in society, not only do we get sleep-deprived doctors, nurses, and students, but we also suffer from unkind and less empathic interactions on a daily basis.”

“It is time as a society to abandon the idea that sleep is unnecessary or a waste and, without feeling embarrassed, start getting the sleep that we need,” she added. “It is the best form of kindness we can offer ourselves, as well as the people around us.”

The study was published in PLoS.