A new study has found that awakening several times throughout the night is more detrimental to people’s positive moods than getting the same shortened amount of sleep without interruption.
For the study, researchers at Johns Hopkins Medicine recruited 62 healthy men and women and randomly subjected them to three experimental sleep conditions in an inpatient clinical research suite: Three consecutive nights of either forced awakenings, delayed bedtimes, or uninterrupted sleep.
The volunteers subjected to eight forced awakenings and those with delayed bedtimes showed similar low positive mood and high negative mood after the first night, as measured by a standard mood assessment questionnaire administered before bedtimes. The questionnaire asked the volunteers to rate how strongly they felt a variety of positive and negative emotions, such as cheerfulness or anger.
Those similarities ended after the second night, according to the researchers.
The forced awakening group had a reduction of 31 percent in positive mood, while the delayed bedtime group had a decline of 12 percent compared to the first day.
Researchers add they did not find significant differences in negative mood between the two groups on any of the three days, which suggests that sleep fragmentation is especially detrimental to positive mood.
“When your sleep is disrupted throughout the night, you don’t have the opportunity to progress through the sleep stages to get the amount of slow-wave sleep that is key to the feeling of restoration,” explained lead author Patrick Finan, Ph.D., an assistant professor of psychiatry and behavioral sciences at the Johns Hopkins University School of Medicine.
Frequent awakenings throughout the night are common among new parents and on-call health care workers, he says. It is also one of the most common symptoms among people with insomnia, who make up an estimated 10 percent of the U.S. adult population.
“Many individuals with insomnia achieve sleep in fits and starts throughout the night, and they don’t have the experience of restorative sleep,” Finan said.
Depressed mood is a common symptom of insomnia, but the biological reasons for this are poorly understood, according to Finan.
To investigate the link, he and his team used a test called polysomnography to monitor certain brain and body functions while volunteers were sleeping to assess sleep stages.
Compared with the delayed bedtime group, the forced awakening group had shorter periods of deep, slow-wave sleep. The lack of sufficient slow-wave sleep had a statistically significant association with the volunteers’ reduction in positive mood, the researchers said.
They also found that interrupted sleep affected different domains of positive mood. For example, it not only reduced energy levels, but also feelings of sympathy and friendliness.
The study also suggests that the effects of interrupted sleep on positive mood can be cumulative, since the group differences emerged after the second night and continued the day after the third night of the study, according to Finan.
“You can imagine the hard time people with chronic sleep disorders have after repeatedly not reaching deep sleep,” he said.
He notes that further studies are needed to learn more about sleep stages in people with insomnia and the role played by a night of recovering sleep.
The study was published in the journal Sleep.