When turning in for the night, a surprising number of people aren’t in the dark.
That may lead to less restful Zzz’s and, eventually, bigger health troubles.
New research finds that even a single night spent in a too-bright room can impair glucose and cardiovascular regulation. This can raise the risk of developing heart disease, diabetes and metabolic syndrome.
“We talk about light a lot in sleep medicine because it’s what drives wakefulness in the daytime,” said Kelly Waters, MD, a neurologist specializing in sleep medicine at Spectrum Health.
“Bright lights cue your brain to say, ‘It’s daytime–time to be awake,'” she said.
But at night, exposure to the blue-light spectrum—TVs, computer screens and smartphones—can inhibit melatonin release.
“And that interferes with sleep,” she said.
The nervous system
A review of the sympathetic nervous system shows why too much light creates problems.
At its extreme, this system governs our fight-or-flight response. Even when we’re asleep, the nervous system is always paying attention.
That vigilance is why your alarm clock works, Dr. Waters said.
Too much light seems to keep the sympathetic nervous system more active, rather than letting you rest and get the necessary restorative qualities of sleep, Dr. Waters said.
“Even asleep, your brain is capturing data,” she said.
In deeper stages of sleep, however, the parasympathetic nervous system rules our “rest and restore” mode, she said.
There are different stages and types of sleep, all necessary for a good night’s rest. A complete sleep cycle lasts between 90 and 120 minutes. Most people cycle through all stages three to four times a night.
They include rapid eye movement, or REM sleep, which is associated with memory processing and accounts for about 10% to 20% of sleep time. It’s also associated with dreaming.
Non-REM sleep is divided into three stages. The first is drowsy, light sleep. This should account for no more than 5% of sleep time. The next is mid-level non-REM sleep, where we spend between 60% to 80% of our sleeping time. And then there’s the deepest non-REM sleep, which accounts for 10% to 20% of sleep time.
These deeper, non-REM stages make us feel refreshed.
“It’s very restorative. That’s where you get growth hormone release,” Dr. Waters said. “It’s a little like opening up lymphatic channels and recycling used nutrients so that you start your day fresh.”
Tame those electronics
While changing sleep patterns and habits is especially important for those battling insomnia or other sleep problems, everyone can benefit from more restful sleep.
Dr. Waters suggests people start by turning off their TV set or removing it from the bedroom entirely.
A poll from the Sleep Foundation reports that 53% of adults watch TV just before bed, often falling asleep while it’s still on.
That’s problematic, she said. First, a television emits the blue-light spectrum, sending confusing “Hey, it’s daytime!” messages to the brain.
Second, the flickering from scene to scene arouses the sympathetic nervous system.
“Your brain is paying attention, even when you’re asleep,” she said. “It’s disruptive.”
Blackout curtains can help, as they shut out streetlights and early morning sunrises. But be aware that prices and effectiveness can vary widely.
Bright clocks and flashing alarm clocks can also trigger alertness.
Dr. Waters said she’s a fan of alarm clocks that simulate sunrise.
“That starts to give people wakeful cues, just when they need them,” she said. “Morning is when you want to activate the brain and give it wakeful cues.”