Good Sleep Guide woman wearing eye shades and sleeping in bed
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Why You Should Sleep with the Lights Off

By Christine Macahilig
February 25, 2023

Reviewed by Susan Ko, Ph.D.

Creating the optimal bedtime routine is important for getting a good night’s sleep. Eliminating distractions or queuing up your playlist are all ways to gently send you off to dreamland. But there’s another thing you should make a part of your regular nightly ritual: turning out the lights. Being exposed to light, whether from lightbulbs or the television, while sleeping may impair heart health and increase insulin resistance, suggests one study.

In the study, conducted by researchers at Northwestern University Feinberg School of Medicine, 20 young adults were split into two groups. Half slept with dim lighting one night and overhead lighting the second night; the other half slept in dim lighting for consecutive nights. The results showed that participants who were exposed to light while sleeping experienced an increase in heart rate and higher blood sugar levels than those who only slept in dim lighting.

The researchers say this suggests that even moderate light exposure at night may negatively affect our overall health for a few reasons. When we're exposed to light in the daytime, it may cause our heart rate to increase as the sympathetic nervous system becomes activated. As a result, we feel alert throughout the day. However, there may also be a similar effect on heart rate when we're exposed to light at night—even artificial light and even while we're asleep.

Furthermore, the researchers posit, nighttime light exposure may affect the body’s ability to regulate glucose levels, which may lead to insulin resistance. With insulin resistance, the cells in the body don't respond to insulin and can’t use the glucose in the blood for energy, causing the pancreas to make more insulin, spiking blood sugar levels over time. A 2020 Japanese study of 678 older adults suggests that low-level nighttime light exposure increases the risk of diabetes.

To avoid the negative health effects of nighttime light exposure, researchers suggest keeping the lights off when you sleep, using blackout shades to keep any outdoor light from coming in, or wearing an eye mask to bed. If you really need to sleep with a light on, keep it dim and closer to the floor.

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