Kill the lights to keep melatonin flowing
Blame Thomas Edison for bad sleep. Too much light before bed is playing tricks on an important sleep hormone.
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On a typical night, you may be staring at a bright computer screen or perhaps glued to your iPad. You eventually stand under the bathroom overhead lights to brush your teeth and then climb into bed with a book as a reading lamp beams over your shoulder.
After awhile you turn off the lights — well, except for the digital alarm clock’s glow, the Internet router’s beacon and the street lamp’s shine seeping through the curtains — and you expect to get a good night’s sleep.
Good luck. You may have messed up your melatonin.
While we know too much light at night disturbs sleep, a new study shows that too much brightness before bed can also suppress the flow of melatonin, the hormone that helps regulate the sleep/wake cycle.
“It’s the biochemical signal of darkness, telling the body it’s a good time to sleep,” explains body clock expert Steven Lockley, author of a study published in the March edition of Journal of Clinical Endocrinology & Metabolism.
Melatonin is secreted in the evening by the brain’s pineal gland, usually starting several hours before sleep occurs. Bright light stops production.
While melatonin isn’t required for sleep — you can doze off on a sunny beach — you have a more natural sleep cycle, and potentially better-quality shut-eye, when you’re in sync with your body clock, explains Lockley.
For hundreds of thousands of years, humans kept a simple schedule, rising in the light and sleeping in the dark. When Thomas Edison invented a long-lasting incandescent bulb a mere 132 years ago, man began seriously illuminating the night. No one questions the benefits of electricity, but sound sleep is not likely one of them.
“We don’t yet understand the full down side of living under this artificial light cycle,” says Lockley, an assistant professor at Harvard Medical School.
Now add the glow of technology. In a U.S. survey of 1,508 people released this week, 95 per cent reported using an electronic device, such as computer, television, video game or cell phone, within an hour of bed at least a few nights a week, according to the National Sleep Foundation.
In addition to the screen light exposure, these interactive devices may over-stimulate the brain before bed — and tempt the user to stay up too late.
Not enough sleep over the long term is associated with bad health, including increased risk of cardiovascular disease and diabetes. Studies have shown that women who work the graveyard shift have increased breast cancer risks. The World Health Organization in 2007 declared that shift work disrupting the body’s internal clock was a probable carcinogen.
While the exact mechanisms causing the health risks still aren’t clear, one promising avenue of research is the study of melatonin interruption from too much light. In animal studies, suppressing melatonin increased the rate of tumour growth, says Lockley, an associate neuroscientist at Brigham and Women’s Hospital in Boston.
But how much light is too much?
In Lockley’s recent study, 116 volunteers were exposed to normal room light or dim light (the equivalent of about three candles) for eight hours before bed over five consecutive days. Blood was continually collected to measure melatonin.
Results showed that exposure to room light shortened the duration of melatonin production by about 90 minutes, compared to the dim light.
“So light in the evening at levels found in homes does suppress melatonin,” explains Lockley. “Just as shift workers have greater health risks, we think this potentially increases health risks, although not as severely as with the shift workers.”
While melatonin supplements are sold over the counter, sleep experts advise against popping the hormone of darkness. “Unfortunately people start using melatonin as if it were a sleeping pill,” explains Colin Shapiro, director of the Sleep and Alertness Clinic at Toronto Western Hospital. “While it might help short term, often the consequence is to shift the body clock in an undesirable way.”
At Rensselaer Polytechnic Institute in Troy, N.Y., scientists found that sitting for two hours in front of a bright computer screen with a white background could potentially suppress melatonin, says Mariana Figueiro, director of the Light and Health program.
Television has less potential to affect the light-sensitive hormone because the viewer sits at a distance, she explains. Most small electronic devices, such as cellphones, tend to emit light below the activation threshold of the circadian system, which regulates biological cycles. But it’s murky: The activation threshold for the circadian system varies by individual. “We cannot make general statements, only potential statements,” she explains.
The iPad, she says, tends to give off somewhat more light and the user could potentially be slightly impacted. “The question is: How much does a little bit of melatonin suppression do to you? Nobody really knows. To be on the safe side, try not to suppress it at all,” advises Figueiro.
The circadian system is most sensitive to short-wavelength, or blue, light. Daylight is saturated with short-wavelength rays. “We are blue-sky detectors. Our sensitivity to low levels of warmer light sources, such as fire, is much lower,” explains Figueiro. “This seems to be a natural adaptation from before the electric light.”
Our cavemen ancestors, snug by the fire, must have slept well.
Expert sleep tips
Sleep researchers offer these suggestions for taking back the night:
• Dim the lights before bed — two hours ahead if possible, but at least a half-hour — while you do something relaxing, such as listen to music or take a hot bath, says Harvard Medical School’s Steven Lockley. “The melatonin will come up earlier, help you fall asleep and have a better quality of sleep.”
• Keep a regular wake-up and bedtime schedule.
• Make sleep a priority. Banish all electronics — the television, computer, smart phone — from the bedroom.
• When you get up during the night, do not turn on the overheads or a bright bulb. If the light that shines through the window isn’t enough for navigating, keep a low-wattage night light, preferably with a red-tinted bulb, which doesn’t disrupt the body clock as much.
Nancy J. White
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