Loneliness and the Evolution of Sleep

A 2025 report by the World Health Organization defined loneliness as “a negative, subjective emotional state resulting from a discrepancy between one’s desired and actual experiences of connection."

Yet a definition doesn’t necessarily help with making sense of it, as Nobel (2023) noted. He viewed loneliness as a “natural biological signal,” akin to thirst or hunger or a flashing light on a mental dashboard signaling a problem.

The sleep light may be simultaneously blinking. In a meta-analysis of 27 articles, Griffin et al. (2020) found an association between loneliness and sleep disturbance, defined as “insomnia symptoms and subjective sleep quality.”

Another meta-analysis of 84 articles found a significant medium correlation between loneliness and sleep difficulties as well as loneliness and certain sleep complaints, such as poor sleep efficiency and loneliness (Hom et al., 2020). In their review of the literature, the authors discussed the idea that poor sleep may be attributed to hypervigilance to social threats in people feeling lonely. “This hypervigilance, in turn, may result in poor sleep quality and restless sleep because the brain remains vigilant even when an individual is asleep,” they added.

This notion is conceivable, given that human sleep has evolved from its start as a communal venture. Samson (2026) related that, until the mid-nineteenth century, it was normal for sleepers to share beds with others, including friends, family, and even strangers.

“From an evolutionary perspective, solitary sleep is unusual because sleep likely evolved within a social safety net,” he shared via email. “When that social context is absent or uncertain, the sleeping brain may remain more vigilant, making loneliness and poor sleep mutually reinforcing.”

Previous research by Simon and Walker (2018) examined if sleep deficit related to loneliness. In the first part of the study, the researchers studied 18 healthy adults who, in subsequent evenings, got either good and bad sleep. Through a social distancing task, the participants then indicated how close they wanted others to get to them. A brain scan of the participants followed, during which they viewed videos of people and objects approaching the camera. After that, participants were recorded answering additional questions.

In the second part of the study, 138 participants kept track of their sleep—specifically their sleep quality—for two nights along with their daytime feelings. In the third part, Simon and Walker asked another 1033 people to view the recorded interviews from the initial segment of the study and rate the participants on behavior and appearance when both well rested and sleep-deprived.

The results were intriguing: When participants got insufficient sleep, they wanted to keep more of a distance from other people. When sleep quality worsened, loneliness was experienced the next day. Finally, the judges in the third part perceived that sleep-deprived participants were lonelier and would be less desirable to have contact with. On top of that, the judges themselves felt lonelier after viewing the videos.

Simon and Walker summarized two key findings from their study: a) the state of sleep loss should be seen as “a social repellent” and b) the asocial effects of sleep deprivation can spread even through brief interactions.

Their findings, according to Samson, are significant. “They suggest sleep loss does not simply make people feel worse internally,” he said. “It may also change social behavior in ways that push others away, creating a feedback loop between poor sleep and loneliness.”

In his view, loneliness interventions can be aided by sleep considerations, not as a cure-all, he added, “but as a modifiable physiological context that shapes vigilance, mood, and willingness to seek connection.”

The connection between slumber and loneliness isn’t one that naturally comes to mind. It is one, however, to sleep on.

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