Screen Light at Night—Distrupts Your Sleep, Worse for Your Health

With Kathryn L.G. Russart, PhD, and Elena A. Christofides, MD

Exposure to light in the hours leading up to bedtime, in particular, the light from electronic devices and television, may be affecting your health, including your weight and blood sugar levels,1 according to study published in Physiology & Behavior.

Even at levels you may think harmless, light exposure at night can trigger a number of health problems, says Kathryn L.G. Russart, PhD, a postdoctoral researcher at Ohio State University Wexner Medical Center in Columbus. She recently reviewed numerous scientific studies that looked at the effects of light at night on human health.1

Difficulty falling asleep at night might be caused by too much blue light from screens.Blue light from computers, smartphones, iPads, and TV add up to poorer sleep, and other health risks.

Time to Tone Down Blue Light from Electronics  

Light at night, she says, is an ''environmental endocrine disrupter.'' While many are familiar with chemical endocrine disrupters, such as PCBs, pesticides, and bisphenol A, all of which have been linked to health problems as well as increased cancer risk, Dr. Russart is focusing on non-chemical endocrine disrupters. And the light at night, emitted from our electronics, unfortunately, plays a starring role.

Our circadian rhythm is geared to 24-hour solar days, and we use environmental cues, such as light, to keep our body clock in sync, Dr. Russart says. Among the tasks guided by our circadian clock is to manage a regular hormonal rhythm in endocrine tissues, which seems to be thrown off by too much exposure to light at night, making it harder to fall asleep. The net result, not enough sleep, but that’s not all.

More worrisome, she tells EndocrineWeb, is a negative impact on blood glucose levels.1 For example, we see from the research that light at night ''can cause weight gain, without an increase in calories, and it can interfere with metabolic function."

Our circadian rhythm is also influenced by the nightly secretion of the hormone melatonin, and light at night inhibits the production of this sleep-promoting hormone, Dr. Russart says. That, in turn, could affect the hormone leptin,3 otherwise known as the satiety hormone that signals your brain that you are full, so when this hormone messaging is thrown off, you gain weight.

As long ago as 1987, some experts also suspected a link between light at night and cancer risk. Since then, several studies have found links between night shift workers and various cancers, including breast, prostate and many others, Dr. Russart says.

How Much Screen Light is Too Much?

"As low as 5 lux of light [the unit of measure scientists use for light] at night can disrupt your circadian rhythm," Dr. Russart says, at least from research in animals.  To put that in perspective, a TV or a cell phone held about a foot away from your face can emit 40 lux. A full moon gives off about 2 lux.

Whatever the sources of light at night—your TV, other electronics, working the night shift—it's a potential long-term health hazard, Dr. Russart says.

The research findings that “light at night is disruptive is dead on accurate," Elena A. Christofides, MD, FACE, an endocrinologist in private practice in Columbus, Ohio, told EndocrineWeb. "These disruptions have been well known for some time." 

These days, she feels that the evidence is so strong about the downsides of night light that she advises all patients, not just those with diabetes, to reduce or avoid light at night.

Dr. Christofides says she especially worries when she sees young children lost in their screens—often a smartphone and their computer, even the TV, simultaneously—getting high levels of light exposure, sometimes well into the night.

Study after study has pointed to the health harms of nighttime light exposure. "It is consistently showing us the same pattern," she says of this latest study.

Tips to Create a Low-Light Action Plan

Dr. Christofides suggests that you use blue light blocking glasses, widely sold online, to reduce the exposure to the blue light from electronics (it also naturally comes from sunlight, which keeps us going during the day).

"My advice is to put the special glasses on around dinner time and keep them on as long as you (and your kids) are using the computer, using your smartphone, on the iPad, and watching TV. The aim is to block out the bluewave-type light, which can make it harder to get to sleep,” she says.

If you go out to dinner, you can leave the glasses behind, she explains. The greatest need is at home when people are typically on the computer, on their handheld devices, and watching television, in the hours leading up to bedtime, she says.

Not everyone agrees the blue light-blocking glasses work, but the data is growing and experts do say health problems can result from too much exposure to blue light before bed.

The effects of the light exposure on your health happen slowly, and are cumulative, Dr. Christofides says, so the effects may not be readily apparent. Nor do people connect light exposure with their health problems.

“When they gain weight or their blood sugar goes up, and she suggests it might be the light at night and impact on sleep; 'they cannot imagine their lifestyle is to blame," she says.

"Disruption of the normal nocturnal rhythm will end badly," she tells her patients.

Based on the evidence, Dr. Russart adds:  "I do think if someone already has diabetes or prediabetes, they should be particularly interested [in the research] and take particular precautions."

Choosing your electronics carefully also may help, Dr. Russart says. "The part of the eye that is affected by light is stimulated in particular by the blue wavelength," she says. "Many phones have built-in apps to lessen some of the blue light."

And try to limit screen exposure in the 2 to 3 hours right before bedtime.

To improve sleep, experts also suggest:

  • Avoid using electronics in the hours before bed.
  • Be sure your bedroom is dark; use heavy window shades if necessary.
  • Consider a sleep mask.

Dr. Russart and Dr. Christofides report no relevant financial disclosures.

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