Sleeping with even a small amount of light can harm your health, study finds
The dim light penetrated the eyelids and disrupted sleep despite participants sleeping with their eyes closed, said study author Dr. Phyllis Zee, director of the Center for Circadian and Sleep Medicine at Northwestern University Feinberg. School of Medicine.
High blood sugar is a sign of insulin resistance, where the body stops using glucose properly and the pancreas goes into overdrive, flooding the body with extra insulin to overcompensate until it finally loses its ability to do so. Over time, insulin resistance can eventually lead to type 2 diabetes.
“Why would sleeping with your lights on affect your metabolism? Could this explain why there is a higher prevalence of diabetes or obesity (in society)?” Zee asked.
Zee and his team took 20 healthy people in their twenties and put them through two nights in a sleep lab. The first night was spent in a dark room where “you wouldn’t be able to see much, if anything, when your eyes were open,” Zee said.
All study participants were connected to devices that monitored a number of objective measures of sleep quality. To ensure data could be collected with minimal interference, they slept with an IV with long tubes that snaked across the room and through a hole to the researcher’s side of the lab. Blood was drawn without ever touching the sleeping participants.
“We recorded the brain waves and could tell what stage of sleep the person was in,” Zee said. “We recorded their breathing, heart rate, electrocardiogram, and also took blood samples from them to measure melatonin levels while they slept.” Melatonin is a hormone that regulates the body’s circadian rhythm, or biological clock for sleep and wakefulness.
A random portion of the group repeated the same light level for a second night in the lab, while another group slept in dim overhead light with a glow roughly equivalent to “a very, very dark, cloudy day. or streetlights coming in through a window,” Zee said.
“Now these people were sleeping with their eyelids closed,” she explained. “In the literature, the estimate is that about 5-10% of the light in the environment would pass through the closed eyelid to the eye, so that’s really not a lot of light.”
Yet even that tiny amount of light created a deficit in slow-wave and rapid-eye-movement sleep, the stages of sleep during which most cell turnover occurs, Zee said.
What to do?
What advice would Zee give people based on her study and existing research in the field? Close your blinds and curtains, turn off all lights, and consider using a sleep mask.
“I think the strength of the evidence is that you clearly have to be careful with the light in your bedroom,” she said. “Be sure to start dimming your lights at least an hour or two before you go to bed to prepare your environment for sleep.”
Check your bedroom for light sources that aren’t needed, she added. If a night light is needed, keep it low and level with the floor, “so it’s more reflective rather than right next to your eyes or level with your bed,” she suggested.
Also be aware of the type of light you have in your bedroom, she added, and banish all lights in the blue spectrum, such as those emitted by electronic devices such as televisions, smartphones, tablets and laptops.
“Blue light is the most stimulating type of light,” Zee said. “If you must have a light on for safety reasons, change the color. You want to choose lights that have more reddish or brownish tones.”
LED lights can be purchased in any color, including red and brownish tones.