Exposure to even moderate ambient lighting during nighttime sleep, compared to sleeping in a dimly lit room, harms cardiovascular function during sleep and increases insulin resistance the next morning, according to a new study from Northwestern Medicine.
There is already evidence that light exposure during daytime increases heart rate via activation of the sympathetic nervous system, which kicks the heart into high gear and heightens alertness to meet the challenges of the day. So closing the blinds, drawing the curtains and turning off all the lights before bed brings heart rate to normal and relaxes the whole body.
The study tested the effect of sleeping with 100 lux (moderate light) compared to 3 lux (dim light) in participants over a single night. The investigators discovered that moderate light exposure caused the body to go into a higher alert state. In this state, the heart rate increases as well as the force with which the heart contracts and the rate of how fast the blood is conducted to blood vessels for oxygenated blood flow.
“The results from this study demonstrate 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. It’s important for people to avoid or minimize the amount of light exposure during sleep.”
Researchers found insulin resistance occurred the morning after people slept in the lightroom. Insulin resistance is when cells in muscles, fat and liver don’t respond well to insulin and can’t use glucose from the blood for energy. To make up for it, the pancreas makes more insulin. Over time, blood sugar level goes up.
An earlier study published in JAMA Internal Medicine looked at a large population of healthy people who had exposure to light during sleep. They were more overweight and obese, Ms. Zee said.
Exposure to artificial light at night during sleep is common, either from indoor light-emitting devices or from sources outside the home, particularly in large urban areas. A significant proportion of individuals, up to 40 percent, sleep with a bedside lamp on or with a light on in the bedroom and/or keep the television on.
Ms. Zee’s top tips for reducing light during sleep include;
- Don’t turn the lights on. If you need to have a light on, make it a dim light that is closer to the floor.
- Color is important. Amber or a red or orange light is less stimulating for the brain. Don’t use white or blue light and keep it far away from the sleeping person.
- Blackout shades or eye masks are good if you can’t control the outdoor light. Move your bed so the outdoor light isn’t shining on your face.