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Study: Curtains or blinds should ALWAYS be closed to get a healthy night’s sleep

The research team discovered that moderate light exposure caused the body to go into a higher alert state.

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By Stephen Beech via SWNS

People wanting a healthy night's sleep should ALWAYS close the curtains or blinds and switch off the bedroom light, according to a new study.

Researchers found that even sleeping in a moderately light room increases the risk of heart disease and diabetes.

Heart rate rises and the body can’t rest properly in a light bedroom at night, say scientists.

Their findings show that 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 following morning.

Senior study author Dr. Phyllis Zee said: “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.”

She says 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.

Dr. Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine said: “Our results indicate that a similar effect is also present when exposure to light occurs during nighttime sleep."

Co-first author Dr. Daniela Grimaldi said: “We showed your heart rate increases when you sleep in a moderately lit room.

“Even though you are asleep, your autonomic nervous system is activated. That’s bad. Usually, your heart rate together with other cardiovascular parameters are lower at night and higher during the day.”

She explained that there are sympathetic and parasympathetic nervous systems to regulate our physiology during the day and night. Sympathetic takes charge during the day while parasympathetic is supposed to at night, when it conveys restoration to the entire body.

The research team found that insulin resistance occurred the morning after people slept in a light room. Insulin resistance is when cells in muscles, fat and liver don’t respond well to insulin and can’t use glucose from blood for energy. To make up for it, the pancreas makes more insulin. Over time, blood sugar goes up.

Dr. Zee said that an earlier study looked at a large group of healthy people who had exposure to light during sleep. They were more overweight and obese.

She said: “Now we are showing a mechanism that might be fundamental to explain why this happens.

“We show it’s affecting your ability to regulate glucose.”

The participants in the study weren’t aware of the biological changes in their bodies at night.

“But the brain senses it,” said Dr. Grimaldi.

“It acts like the brain of somebody whose sleep is light and fragmented. The sleep physiology is not resting the way it’s supposed to.”

The researchers explained that 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.

Up to four in 10 people sleep with a bedside lamp on or with a light on in the bedroom or keep the television on.

Dr. Zee said: “In addition to sleep, nutrition and exercise, light exposure during the daytime is an important factor for health, but during the night we show that even modest intensity of light can impair measures of heart and endocrine health."

The study tested the effect of sleeping with 100 lux (moderate light) compared to three lux (dim light) in participants over a single night.

The team discovered that moderate light exposure caused the body to go into a higher alert state. In that 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.

Dr. Zee said: “These findings are important particularly for those living in modern societies where exposure to indoor and outdoor nighttime light is increasingly widespread."

She gave three top tips for reducing light during sleep:

  • Don’t turn lights on. If you need to have a light on, which older adults may want for safety, make it a dim light that is closer to the floor.
  • Color is important. Amber or a red/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.

Dr. Zee added: “If you’re able to see things really well, it’s probably too light."

The findings were published in the journal Proceedings of the National Academy of Sciences (PNAS).

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