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A study found losing just one hour of rest could kill people’s desire to help others, even relatives and close friends. The team noted that a bad night appeared to dampen activity in the part of the brain that encouraged social behavior. “We discovered that sleep loss acts as a trigger of asocial behavior, reducing the innate desire of humans to help one another,” said Prof Matthew Walker, co-author of the study at the University of California, Berkeley. “In a way, the less sleep you get, the less social and more selfish you become.” Writing in the PLoS Biology journal, the team suggest that a chronic sleep deficit could harm social bonds and compromise the altruistic instincts that shape society. “Considering the essentiality of humans helping in maintaining cooperative, civilized societies, together with the robust erosion of sleep time over the last 50 years, the ramifications of these discoveries are highly relevant to how we shape the societies we wish to live in,” said Walker.

The team examined the willingness of 160 participants to help others with a “self-reported altruism questionnaire”, which they completed after a night’s sleep. Participants responded to different social scenarios on a scale from “I would stop to help” to “I would ignore them.” In one experiment involving 24 participants, the researchers compared answers from the same person after a restful night and after 24 hours without sleep. The results revealed a 78% decline in self-reported eagerness to help others when tired. The team then performed brain scans of those participants and found a short night was associated with reduced activity in the social cognitive brain network, a region involved in social behavior. Participants were as reluctant to assist friends and family as strangers, the researchers said. “A lack of sleep impaired the drive to help others regardless of whether they were asked to help strangers or close relatives. That is, sleep loss triggers asocial, anti-helping behavior of a broad and indiscriminate impact,” said Walker.

To determine whether altruism takes a hit in the real world, the team then tracked more than 3m charitable donations in the US before and after clocks were shifted an hour forward to daylight saving time, suggesting a shorter period of sleep. They found a 10% drop in donations after the transition. “Our study adds to a growing body of evidence demonstrating that inadequate sleep not only harms the mental and physical wellbeing of an individual but also compromises the bonds between individuals, and even the altruistic sentiment of an entire nation,” said Walker. Luckily, we can catch up on sleep. Walker said: “The positive note emerging from all our studies is that once sleep is adequate and sufficient the desire to help others is restored. But it’s important to note that it is not only sleep duration that is relevant to helping. We found that the factor that was most relevant was actually sleep quality, above and beyond sleep quantity,” he added.