You’ve heard the warnings: Stare at your cell phone or tablet too long before bed and you might miss out on precious sleep. But could that artificial glow also boost your risk of cancer, obesity, depression, and other problems?
Studies have long suggested that exposure to excess artificial light at night throws off our circadian rhythm, or biological clock. Now research is finding that so-called blue light may have the potential to do damage beyond robbing you of a good night’s sleep. “It is a looming public health crisis,” says Charles Czeisler, PhD, MD, chief of the division of sleep and circadian disorders at Brigham and Women’s Hospital in Boston. Here’s what you need to know.
Why blue light matters
Open your blinds in the morning and, the instant the light streams in, a complex series of physiological processes ensue. Specialized cells in your eyes detect this light and tell your brain to shut off production of sleep-inducing melatonin. Cells crank up production of the stress hormone cortisol and the hunger-promoting hormone ghrelin. Body temperature and heart rate rise. In essence, your body clock resets every cell to “daytime physiology,” explains Richard Stevens, PhD, a cancer epidemiologist at the University of Connecticut.
That’s great when it’s actually morning, but get too much light at night and things start to go awry. Research shows that people exposed to blue-enriched light (the kind that emanates from electronics, eco-friendly compact fluorescent lights, and LEDs) at night are hungrier and eat more than those who aren’t. One landmark study, co-authored by Czeisler in the journal PNAS, found that people who read from an e-reader before bedtime took longer to fall asleep, experienced less restorative REM sleep, and were sleepier the next morning than those who read from a paper book. Over the course of just 5 days, they also saw their nighttime melatonin levels drop by 55%. (Boost your memory and age-proof your mind with these natural solutions.)
That last bit is particularly worrisome, researchers say, because the hormone melatonin does more than make you feel sleepy; it’s been shown in numerous animal studies to be a potent anti-cancer agent. “When we subject laboratory animals to light at night and knock out the melatonin signal, the tumors develop sooner, grow faster, are more active, and are more likely to metastasize,” says David Blask, PhD, MD, associate director of the Tulane University Center for Circadian Biology.
Meanwhile, researchers at Ohio State University have found that when they expose rodents to even dim light at night—like a street light shining in the window or a TV glowing in the corner—for 8 weeks, their brain becomes inflamed and they act depressed (which is also a thyroid symptom that you should watch out for). They also store more fat and become glucose intolerant (a risk factor for diabetes).
What does all of this mean to humans long-term?
The science is too young to say for sure. But some recent studies suggest that those whose nights are more illuminated are more likely to be obese or suffer from heart disease. Many well-regarded studies also show that night shift workers are 50 to 80% more likely to develop breast cancer and up to three times as likely to develop prostate cancer. And with our late-night email checking and Facebook browsing, “in a sense, we are all night shift workers to a degree now,” says Blask.
What to do about it
Should you throw out your laptop and start lighting your home with candles? Absolutely not, says Stevens. But making some simple changes may help you protect your health.
Power down. Shut off all of your electronics at least 1 hour before bedtime.
Read a real, paper book. Studies show e-readers disrupt sleep and melatonin production. If you must go with an e-reader, invest in a screen protector such as iLLumiShield, which filters out some of the troublesome wavelengths.
Get the app. The f.lux app automatically prompts your laptop or smartphone to emit blue light by day and shift to warmer wavelengths by night.
Customize your lights. Companies like Phillips and Lighting Science make energy-efficient bulbs that change hue depending on the time of day.
Black it out. If you live in an urban area where ambient light from the streets comes in your window, invest in blackout curtains and a sleep mask.