The National Sleep Foundation in the United States recommend that teenagers get 8–10 hours of sleep a night and that adults under 65 years of age get 7–9 hours.
However, almost one-third of adults who responded to the 2012 National Health Interview Survey reported that they slept less than 6 hours a night.
Most research into the cognitive and emotional effects of sleep deprivation involves volunteers spending several nights in the unfamiliar surroundings of a sleep laboratory.
Psychologists in Norway wanted to investigate the effects under more natural circumstances, while people were at home and sleeping in their own beds.
They discovered that less sleep led the participants to feel worse the next day, but not in the sense of feeling down or depressed. Rather, they experienced fewer positive emotions.
“They felt less joy, enthusiasm, attention, and fulfillment,” says Ingvild Saksvik-Lehouillier, associate professor of psychology at the Norwegian University of Science and Technology, who led the research.
The psychologists say that their findings indicate that staying up late on work or school nights could impair people’s ability to manage stress and negative life events.
“We already know that fewer positive emotions have a major impact on mental health,” says Saksvik-Lehouillier. “We also know that poor sleep is included in virtually all mental health diagnoses.”
After getting less sleep than normal, study participants also behaved more impulsively and were more prone to making mistakes on a standard test.
The research features in the journal Sleep.
The study tracked 52 healthy adults aged between 18 and 35 years over a period of 11 days.
To monitor sleep, the researchers asked the volunteers to wear motion sensors on their wrists and fill out a “sleep diary” every morning. The diary included questions about what time the person went to bed and got up, how long it took them to fall asleep, and any periods of wakefulness during the night.
After maintaining their normal sleep habits for 7 days, the participants went to bed 2 hours later than usual for the last 3 nights of the study but got up at their regular time.
“In the imposed sleep deprivation phase, participants crawled under their covers 2 hours later than they normally did and had to get up at their usual time,” says Saksvik-Lehouillier.
On the morning of days 1, 4, and 8 during the habitual sleep phase, and days 9 and 11 during the sleep deprivation phase, they performed a test at the lab at about 9 a.m.
The standardized test, called the Conners’ Continuous Performance Test-3, involves pressing the spacebar on a keyboard whenever any letter of the alphabet — apart from the letter “X” — appears at random locations on a screen.
The test is designed to assess an individual’s capacity for sustained attention and vigilance. It lasts 14 minutes, during which time, 360 letters pop up at irregular intervals on the screen.
After the attention test, the participants filled out a standard questionnaire called the Positive and Negative Affect Schedule, which assesses emotional state.
This test required them to score themselves on 10 types of positive emotion, such as excited, determined, and alert, as well as 10 types of negative emotion, such as afraid, guilty, and nervous.
Crucially, the participants were not allowed to consume caffeinated drinks from the time they got out of bed until after they had taken the tests.
On the mornings after the 3 late nights, the participants’ response times decreased on the attention test, which suggests that they were becoming more impulsive.
However, they made progressively more mistakes over the 3 days.
“We didn’t find clear differences when it came to the negative emotions, but there were marked differences for the positive ones,” says Saksvik-Lehouillier. “Positive feelings scored worse after just 1 night of reduced sleep and dropped even more after 3 nights.”
The psychologists write that their findings may be a more accurate reflection of the effects of sleep deprivation on daily life than those that lab-based experiments provide. In the lab, researchers typically restrict participants’ sleep to only 4 or 5 hours a night.
The authors conclude:
“These findings highlight that even 1–2 hours less sleep for a few nights is associated with negative consequences. Also, these findings show that even a small lack of sleep may have important implications for everyday function and quality of life, such as social interaction, work efficiency, and traffic safety, especially in the early morning.”
The authors note that one possible limitation of their study was that 79% of participants were female, which could have introduced a gender bias to the results.
Previous research suggests that females may be more vulnerable than males to the effects of sleep deprivation and that they may also experience more problems with sleep.
