Sleep loss, ranging from the individual level of missing a night's sleep to a societal level of losing an hour's sleep because of Daylight Saving Time, is associated with reduced altruism or an inclination to help others, new research suggests.
These effects were observed even at the neurologic level on brain MRIs, investigators report.
"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," lead author Eti Ben Simon, PhD, Center for Human Sleep Science, Department of Psychology, University of California, Berkeley, told Medscape Medical News.
"The study adds to a growing body of evidence demonstrating that inadequate sleep not only harms the mental and physical well-being of an individual, but also compromises the bonds between individuals — and even the altruistic sentiment of an entire nation," Ben Simon said.
The findings were published online August 23 in PLOS Biology.
Decreased Desire to Help
With previous research showing that brain changes such as lesions can affect the social cognition network in the brain and, consequently, even levels of empathy and compassion, the current investigators sought to examine how another known detrimental factor (sleep loss) might affect that region — specifically in terms of altruistic decision-making.
In the first of their three studies, 23 individuals (mean age, 20 years; 54% women) were assessed with a 40-item questionnaire from the Self-Report Altruism Scale following two conditions: one after a rested night of sleep and one after 24 hours of sleep deprivation.
The two sessions were separated by at least 7 days. Participants were randomly assigned to start either with the sleep deprivation or full night's sleep session.
Items on the questionnaire included scenarios such as, "If I was in a hurry to get to work and someone stopped me to ask for directions I would…" or "I would help a stranger struggling with her grocery bags to carry them." The scale of possible responses ranged from "I would definitely help" to "I would ignore them."
Results showed significant decreases in the altruistic responses after the night of sleep deprivation among as many as 78% of participants compared with their responses after a full night's sleep (P = .011).
Reductions in altruism were independent of the confounders of fatigue-related mood changes or reductions in motivational effort (P < .01), and the effect was also independent of differences in individual levels of empathy.
Surprisingly, the reduced altruism after sleep impairment did not only apply to strangers, but also in scenarios of helping friends or colleagues — with no significant differences between the two.
"Interestingly, and contradicting classical theories that posit individuals are more likely to help their closest kin, a lack of sleep impaired the drive to help others regardless of whether they were asked to help strangers or close relatives," Ben Simon said.
"That is, sleep loss triggers a phenotype of asocial behavior with a broad and indiscriminate impact," she added.
Changes Reflected on MRI
In further analysis, functional MRI (fMRI) evaluation of the 23 participants showed the night of sleep impairment was associated with a significant reduction in task-evoked activity within the social cognition network, known to be involved in prosocial behaviors (P = .02).
Furthermore, the magnitude of impairment in the social cognition network on fMRI caused by sleep loss corresponded with the decrease in altruism (P = .046).
Similar changes were not observed in any other standard functional brain networks, such as in the salience network, associated with empathy and social-emotional functioning.
The changes on MRI were also not associated with positive and negative moods relating to sleep loss or reduction in motivational efforts.
"These neural data highlight a central neural pathway underlying the profile of asocial behavior caused by sleep loss," Ben Simon said.
In a second study, the investigators evaluated the role of sleep efficiency over time in 171 participants (mean age, 37 years), with a total of 136,441 observations.
Results showed that worse self-reported sleep efficiency from sleep diaries was again associated with next-day decreases in the expressed desire to help others (P < .05), with those findings also independent of trait empathy scores and sleep-related changes in mood.
"Such findings suggest that poor sleep, either across individuals or relative to one's own habitual sleep profile, significantly and robustly reduces prosocial helping," the researchers write.
"Spring Forward" Effects
In the third study, the investigators sought to examine the effect on a macro level by assessing patterns of charitable donations following Daylight Saving Time, when the population in most US states loses an hour of sleep during the "spring forward" transition.
The analysis included more than 3 million charitable donations that were made between 2001 and 2016. To avoid the influence of seasonal changes on donation patterns, average donations were compared between the Daylight Saving transition and those in the month before and after the time change.
Its findings showed a significant decrease in donations in the period around the Daylight Saving shift compared with the other two periods, with an approximately 10% reduction in donations during the time change (P < .005).
Further analysis evaluated whether the lower donations could represent not the loss of an hour's sleep, but the loss of an hour during the day available to make donations. However, adjustment for that lost hour showed similar results.
Importantly, the same reduction of compassionate gift-giving was not observed in regions of the US that did not observe Daylight Saving Time.
"This latter finding was perhaps the most surprising to us," Ben Simon said.
"Even just 1 hour of sleep loss was more than enough to influence the choice to help another," she added.
With data from the National Sleep Foundation indicating that more than 50% of individuals in first-world nations report not getting sufficient sleep during workdays, the findings may have broad implications, the investigators note.
However, while showing negative effects of impaired sleep, "the findings also conversely highlight adequate sleep as a modifiable factor to promote greater helping," they write.
"This is in contrast to more fixed features, such as personality traits or broader cultural edicts that are likely to be challenging to target as interventional methods for promoting prosocial helping," they add.
Commenting for Medscape Medical News, Andrew Coogan, PhD, professor of Behavioral Neuroscience, Department of Psychology, Maynooth University, Kildare, Ireland, said the study represents a "valuable addition to our understanding of the importance of sleep" for a whole range of behaviors.
"Short/insufficient sleep is a societal issue and, as such, appreciating the social and interpersonal aspects of sleep loss is key to understanding the broader societal and social impacts of poor sleep in the general population," said Coogan, who was not involved with the research.
He noted the changes observed with Daylight Saving Time are especially resonant.
"The switch to Daylight Saving Time increases something called social jetlag, which is in essence the mismatch between the internal time of our body's circadian clock and the social schedules that we keep," Coogan said.
Previous research has shown that living in western parts of time zones, which is associated with greater social jetlag and therefore shortened sleep, is also associated with "less prosocial behavior," he noted.
"The current real-world data showing a decrease in charitable donations around the DST transition is consistent with previous findings," said Coogan.
The investigators and Coogan have reported no relevant financial relationships.
PLOS Biology. Published August 23, 2022. Full text
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Cite this: Sleep Loss Linked to Reduced Generosity, Even at a Neuronal Level - Medscape - Aug 30, 2022.