Sleep deprivation can affect people’s unconscious attitudes toward minorities, according to new research published in Scientific Reports.

The study found that chronic sleep restrictions made Americans more hostile to Arab Muslims.

“Lack of sleep is common to most all of us in our society. And it is particularly relevant to first responders and other professionals such as police, firefighters, and military personnel,” said study author William D. “Scott” Killgore, a clinical neuropsychologist and research neuroscientist at the University of Arizona.

“I have been working with the military for about 15 years to understand how lack of sleep affects human judgment and decision making in critical situations,” he told PsyPost. “I have been interested to understand the potential role that sleep loss can play in critical decision making contexts, particularly when dealing with racial minorities or people of different ethnic backgrounds.”

“These kinds of decisions often make headlines in the news, particularly when they involve police or others who interact with groups in highly emotionally charged and potentially hazardous situations.”

In the study, seventeen young healthy adults lived inside an isolated sleep lab for two separate 25-day periods. During one of these periods, the participants were allowed 8 hours of time in bed every night. In the other period, they were only allowed 4 hours a night in bed on weekdays, followed by a weekend of recovery sleep of 8 hours.

On day 21 of each period, the participants completed an Implicit Association Test (IAT), in which they rapidly categorized names that flashed on a computer screen. The well-studied test is commonly used to measure hidden biases, which the participants themselves might not even be aware of. In this case, the test was focused on Arab Muslims.

The researchers found that fully-rested participants had no bias against Arab-Muslim names. But the same participants did display negative bias towards Arab-Muslim names when they were chronically sleep restricted.

“Sleep is more important than we think, and it doesn’t just affect how tired we feel and our work performance,” Killgore told PsyPost. “It also can unmask deep hidden unconscious attitudes that we normally try to keep suppressed and under control.”

“At a minimum, this has the potential to affect the quality our relationships with others, but at worst, it has the potential to affect our split-second responses to others in critical life-and-death situations,” he added. “Getting 7-8 hours of sleep every night is critical, not only for our health and work performance, but also for how we relate to others.”

The study’s longitudinal design allowed the researchers to make inferences about cause and effect — rather than just report a correlation. But the research does have some limitations.

“The study sample was small, so the findings need to be replicated,” Killgore explained. “Also, the Implicit Association Test (IAT), measures unconscious biases toward particular groups, but it is not clear how these biases actually extend to real-life prejudicial behaviors or actions. Further research into whether these biases actually translate into discriminatory behavior still needs to be done.”

The researchers used a racially diverse sample. Seven participants identified as Caucasian, eight as African American, one as Asian and one as Native American.

“There is no substitute for sleep,” Killgore said. “Our research has also shown that many of the emotional deficits that occur during sleep deprivation are not fully reversed by stimulants or wake-promoting agents like caffeine. Caffeine may make you feel awake, but it does not replace sleep and you may still be prone to making errors in judgment.”

The study, “Chronic Sleep Restriction Increases Negative Implicit Attitudes Toward Arab Muslims“, was also co-authored by Anna Alkozei, Ryan Smith, Natalie S. Dailey, Sahil Bajaj and Monika Haack. It was published online June 27, 2017.