Even Moderate Ambient Light During Sleep Is Harmful – Increases Risk for Heart Disease and Diabetes

Bad Sleep Concept

Close the Blinds During Sleep To Protect Your Health

  • Exposure to artificial light at night during sleep is common
  • Sleeping in a moderately light room increases risk for heart disease and diabetes
  • Your heart rate rises, and body can’t rest properly in light bedroom at night

Close the blinds, draw the curtains and turn off all the lights before bed. Exposure to even moderate ambient lighting during nighttime sleep, compared to sleeping in a dimly lit room, harms your cardiovascular function during sleep and increases your insulin resistance the following morning, reports a new Northwestern Medicine study.

“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,” said senior study author Dr. Phyllis Zee, chief of sleep medicine at Northwestern University Feinberg School of Medicine and a Northwestern Medicine physician. “It’s important for people to avoid or minimize the amount of light exposure during sleep.”

There is already evidence that light exposure during daytime increases heart rate via activation of the sympathetic nervous system, which kicks your heart into high gear and heightens alertness to meet the challenges of the day.

“Our results indicate that a similar effect is also present when exposure to light occurs during nighttime sleep,” Zee said.

The study was published on March 14, 2022, in PNAS.

Heart rate increases in light room, and body can’t rest properly

“We showed your heart rate increases when you sleep in a moderately lit room,” said Dr. Daniela Grimaldi, a co-first author and research assistant professor of neurology at Northwestern. “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.”

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

How nighttime light during sleep can lead to diabetes and obesity

Investigators found insulin resistance occurred the morning after people slept in a light room. Insulin resistance is when cells in your muscles, fat and live don’t respond well to insulin and can’t use glucose from your blood for energy. To make up for it, your pancreas makes more insulin. Over time, your blood sugar 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, Zee 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,” Zee said.

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

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

Exposure to artificial light at night during sleep is common

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%) sleep with a bedside lamp on or with a light on in the bedroom and/or keep the television on.

Light and its relationship to health is double-edged.

“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,” said co-first author Dr. Ivy Mason, who at the time of the study was post-doctoral fellow at Northwestern and now is a research fellow at Harvard Medical School.

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 called sympathetic activation. 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 your blood vessels for oxygenated blood flow.

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

Zee’s top tips for reducing light during sleep

  1. 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.
  2. 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.
  3. 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

Is my room too light?

“If you’re able to see things really well, it’s probably too light,” Zee said.

Reference: “Light exposure during sleep impairs cardiometabolic function” by Ivy C. Mason, Daniela Grimaldi, Kathryn J. Reid, Chloe D. Warlick, Roneil G. Malkani, Sabra M. Abbott and Phyllis C. Zee, 14 March 2021, Proceedings of the National Academy of Sciences.
DOI: 10.1073/pnas.2113290119

Other Northwestern authors are Kathryn Reid, Chloe Warlick, Roneil Malkani, and Sabra Abbott.

The title of the article is “Light exposure during sleep impairs cardiometabolic function.”

The research was supported, in part, by the National Center for Advancing Translational Sciences grant 8UL1TR000150-05, National Heart, Lung, and Blood Institute grant R01 HL140580, National Institute of Aging grant P01AG11412, all of the National Institutes of Health, and the American Heart Association.

10 Comments on "Even Moderate Ambient Light During Sleep Is Harmful – Increases Risk for Heart Disease and Diabetes"

  1. Paul Schwartz | March 15, 2022 at 4:35 pm | Reply

    What lies. If this were true, Alaska woulds have the highest rates of disease in the nation. It doesn’t.

    • You need to stop the lies on lying. Get an education on reading comprehension. First the article states getting sleep is the priority not where you live, which is blacken the room where you sleep.
      They are correct on keeping the eyes covered with no lights in the room. I read everything on trying to get to sleep and getting a few more hours of sleep. I sleep on average 4-4.5 hours a night and that doesn’t count at what time I go to sleep. I have experimented for over 70 years on how I can get to sleep and get more sleep.
      I already knew half of this stuff already. Not the ramifications of the lack of sleep pointed out here in this article. I’ll will point out that it’s very hard for me to sleep during the day with the light pressure on my body.

  2. This is alarmist, my bed is 5 feet from my computer monitor, it receives about 3 Lux with the meter facing the screen. They are defining moderate light as a well lit area. With 2 reading lamps and the computer monitor on the light at the bed ( within 5 ft of all three light sources) still only reads at 13 lux, directly under a reading lamp I read 366 Lux. Too much light may be bad for you but 100Lux is a lot of light.

  3. How many people in this study? If it’s 500 or more, I might consider it. If it’s 10 or 20, there’s no value to the study at all. Why don’t they state the parameters of the study?

    • The study involved 20 students. Not once was that number mentioned in this article. For balance, the article should have included reactions from experts not involved in the study.

  4. From the publication: “A total of 20 healthy adults were randomized into the room light condition (n = 10, one night in dim light < 3 lx followed by one night with room light at 100 lx) and the dim light condition (n = 10, two consecutive nights in dim light < 3 lx)" Even with this small sample size, there were some significant differences in physiologic parameters the next day for sleeping in dim light or moderate light the night before. Many of these parameters are associated with poor health outcomes. However, in the case of this study these parameters are all surrogate markers of risk of poor health outcomes. A much larger epidemiologic study would be the way to go, if even feasible. The study itself appeared to be rigorously done, and the methodology looks fairly standard for measuring insulin resistance, insulin, blood glucose, heart rate variability, etc.

  5. Daytime Naps will now kill you!
    Fall asleep at the beach AND DIE!!!

  6. This all makes sense. I don’t have blinds, I live deep in a forest clearing with giant windows, floor to ceiling but nights are dark enough. No street lights and city lights brightening the sky. Only problem bright moons full or otherwise make me moody and tired next day. If there is even a crack of artificial light the same, I just cannot get to sleep properly. Hotel lighting is the bane of my existence. I travel with block out tape to cover light switches, air-con switches, every on off button is illuminated, a galaxy of irritating light. The tape also comes in useful for flying, those lights are a couple of feet from your face. Business class seats are the worst as every position of the seat has an illuminated switch……..I cant sleep with those eye mask they give you in the kits. At times I have had to make a tent out of the blanket the ambient light has been so bad. An ideal long haul for me would be in complete darkness with maybe just a few passage lights set very low and dim. People read and fall asleep leaving their lights on which is incredibly anti-social.. You have to call the hostess to put them all off. Airways should definitely start appreciating how much we need light free sleep.
    I think some people have a lower tolerance for light, though. Children also manage to sleep through broad daylight no problem. I think if bright light was a constant it would certainly affect my health badly, pure stress.

  7. In Alaska people won’t sleep in the open to get exposed to light for 6 months in the year.

  8. Very Interesting Research.

    Some thoughts.
    1. Light is a source of energy. It is perceived vide the sense of sight.
    2. Light Iluminates and enables us to see the world.
    3. We too are objects with consciousness and perceptual abilities.
    4. Light from the sun provides us the suns rays which includes the rays of the visble spectrum and infra red as heat. The Ultra Violet is mostly filtered out thanks to the Ozone Protectve layer.
    5. These rays are absorbed by our skin and is another method of directly providng energy required by the bodies cells. How deep these rays penetrate depends on how thick skinned we are and the colour of the skin. Dark Skinned people probqably have the superior ability to handle the suns rays.
    6. Sample size of 20 for the study is insufficient.
    7. Sleep cycles and lighting or lack of it, needs to be re-examined in light of (1) to (5).
    8. Different individuals have different abilities to get sleep [REM Sleep, Deep Sleep, Unconscious (like a log) Sleep, dreamless sleep].
    9. You can see lots of people dozing off under the shade of trees, in all parts of the world incuding India.

    Views expressed are personal and not binding on anyone

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