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Sleeping With Even a Little Ambient Light Could Harm Your Health: Study

Young Black woman using her phone with light on while relaxing in bed

Do you like to fall asleep to the flickering glow of your favourite shows on the TV? Sadly, it may be better to limit your viewing time (and light exposure) to your waking hours. While it may be comforting to go to sleep with a little ambient light — according to a new study from Northwestern Medicine — even a moderate amount of light exposure while sleeping can be harmful to your health.

Related: Why a good night’s sleep may be good for your heart.

Can light affect your sleep cycle — and health?

The parallel-group laboratory study — which tested different sleep conditions on a small sample of 20 healthy young adults — found that just one night of exposure to light during sleep could have negative implications for a variety of health factors. One night of moderate room lighting exposure (of 100 lx), the study found, could increase your nighttime heart rate while lowering your heart rate variability, compared to sleep in a dimly lit sleep environment (of <3 lx). Moreover, a single night of moderate room lighting exposure could also increase your next-morning insulin resistance in comparison to a dimly lit environment.

As senior study author Dr. Phyllis Zee — chief of sleep medicine at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician — explained in Northwestern Now, the study’s results show that “just a single night of exposure to moderate room lighting during sleep can impair glucose and cardiovascular regulation, which are risk factors for heart disease, diabetes and metabolic syndrome.” 

See also: 10 reasons you can never get enough sleep.

What can you do to keep light out from your sleep time?

The good news? There are some simple steps you can take to optimize your bedroom space for better sleep by minimizing potential light exposure. Some tips, which we adapted from the Northwestern Now, include:

  • Keep the lights off — or, at the very least — low. If you can turn off all lights at bedtime, this could be great for your sleep. However, if you need a small light on for safety reasons, opt for a dim light that’s close to the floor and not at eye level.
  • Consider colour. Think carefully about the colour of light in your sleep space. White or blue light, for example, may disrupt your sleep cycle — so opt for amber or red or orange light around your bedtime area, where possible.
  • Look for ways to shut out the light (literally). If natural light is creeping in (for example, if you sleep during the day because of shift work), consider finding ways to block out the light, such as blackout curtains or a sleep-time eye mask.

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