Getting a good night's sleep is one of the most important things you can do. Not only is it key to physical health, it also improves mood and overall mental health. But it's not just how much sleep we get; according to new research, getting woken up in the middle of the night will do more to turn you into a sourpuss than staying up late or waking up early.
Around 30 percent of people suffer some symptoms of insomnia, and 10 percent meet the diagnostic criteria for insomnia, which includes feeling distress or some kind of impairment as a result of sleepless nights. Despite those numbers, there's not a whole lot of information out there on how insomnia works. Researchers know people with insomnia often wake up several times a night and generally get less sleep than others, and they know that insomnia leads to depression and poor mood—no surprises there. But what exactly is it about insomniacs' sleep patterns that gets people moody and depressed? So far, scientists who study sleep haven't been able to figure that out.
"Partial sleep loss from sleep continuity disruption is more detrimental to positive mood."
Patrick Finan, a professor of psychiatry and behavioral sciences at Johns Hopkins University, and his colleagues Phillip Quartana and Michael Smith, figured the insomnia-mood link could be more complicated than just lack of sleep at all. Poor mood, they theorized, might result from not getting enough deep sleep (the period that follows dreaming). Because it takes a while to reach that stage after falling asleep, waking up in the night could reduce the amount of deep sleep each person gets, even compared to someone who sleeps the same amount of time but without interruption.
To test that idea, Finan, Quartana, and Smith watched 62 healthy men and women sleep for five nights—except that during three consecutive nights, nurses came in eight times, woke 21 of their charges up, and forced them to stay awake for a total of at least three hours and 20 minutes, meaning those sleepers got at most four hours and 40 minutes of sleep. Seventeen other participants went to bed late and slept for the same amount of time but without interruptions, and 24 people slept eight marvelously uninterrupted hours. To track mood, participants recorded both positive and negative feelings each day.
Compared to eight-hour sleepers, the others reported a worsening mood as the days went on, but the effect was worse for interrupted sleepers—in particular, they reported fewer positive feelings than those who got brief but uninterrupted sleep. A follow-up analysis showed that was at least in part due to limiting how much deep sleep participants got.
"[D]espite comparable reductions in total sleep time, partial sleep loss from sleep continuity disruption ... is more detrimental to positive mood" than simply not sleeping very long, the team writes in the journal Sleep. The results are preliminary for a number of reasons, they add, but could help researchers better understand insomnia in the future.
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