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how did you sleep last night Your answer may depend on how long you’ve been in bed, how long you’ve spent tossing and turning, or whether you rest at all. But you may or may not have exercised today, depending on what your wearable device says or what you’re asked.
This article is part of a special series investigating key questions about sleep. Read more here.
“Everyone has their own definition of sleep quality, and that’s the problem,” says the sleep researcher Nicole Tang at the University of Warwick, UK.
Although scientists are still figuring out the puzzle of sleep quality and what defines it, we do know that a good night’s rest involves sleep cycles, the different sequences of phases of brain activity we experience during sleep (see diagram below). And for most of us, each stage of these cycles is necessary to wake up refreshed. The average person experiences four or five full cycles a night and disrupting these can have both short-term and long-term health consequences.
“Poor sleep quality is associated with many adverse physical health outcomes,” he says Jean-Philippe Chaput at the University of Ottawa in Canada. Similar to what you might expect from not getting enough sleep (see “Why Your Chronotype Is Key to Knowing How Much Sleep You Need”), among them there is a greater risk cardiovascular disease, the stroke, hypertension, type 2 diabetes and weight gain.
Although there is no definitive consensus on what defines sleep quality, researchers and doctors often study sleep with an electroencephalogram (EEG), which tracks brain activity during sleep…
