When it comes staying in a good mood, getting a decent chunk of uninterrupted sleep is better than getting woken up repeatedly, according to a new study, something that is well-known to shift workers, insomniacs and many new parents.
The study by researchers at the Johns Hopkins University School of Medicine looked at whether sleep disruption or time of sleep was an indicator of mood changes in people with insomnia, chronic pain or other sleep-related disorders.
So the researchers put volunteers through three nights of seeming hell: getting woken up a random 20 minute period each hour for seven hours, plus a full hour once a night.
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Needless to say, the volunteers self-reported states of positive emotion was pretty slow, according to Patrick Finan. lead author of the paper appearing in the journal Sleep, and an assistant professor of psychiatry and behavioral sciences at JHU.
"It was pretty harsh," Finan admitted. "It was a sledgehammer approach. It would be more severe than clinical insomnia."
The two others groups included people who were allowed to sleep normally, and those who were on a "sleep-restricted" group. That means they were allowed to sleep for the same amount of time as the people who were woken up. The participants were asked to rate how strongly they felt a variety of positive and negative emotions, such as cheerfulness or anger. The differences emerged after the second night: 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.
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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.
Finan said this means that the quality rather than the quantity of sleep is important in maintaining positive mood. He said the forced awakenings, which happens to people who suffer from insomnia, affects their ability to obtain deep "slow-wave" sleep, which is associated with a number of health problems, including depression.
"It was the change in slow-wave sleep that is particularly important," he said. The study "gives us information about the patterns of sleep loss that seem to be particularly important for how we regulate our mood from day to day."
Frequent awakenings throughout the night are common 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.
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A depressed mood is a common symptom of insomnia, Finan says, but the biological reasons for this are poorly understood. To investigate the link, he and his team used a test called polysomnography to monitor certain brain and body functions while subjects were sleeping to assess sleep stages.
Finan says the study also suggests that the effects of interrupted sleep add up over time, since the group differences emerged after the second night and continued the day after the third night of the study.
He says the next phase will be to study people who actually suffer from these night time awakenings.
Daniel Buysse, professor of psychiatry and clinical and translational science at the University of Pittsburgh, said the study answers some important questions about the debate between quality versus quantity of sleep.
"It demonstrates that sleep is important for our emotional health, and two that its not all about sleep duration," Buysse told Discovery News. "There's been a huge amount of information in press about impairments associated with inadequate sleep duration. This article points out its not just the amount, but how consolidated it is that also matters."