Why We Sleep's Matthew Walker on the Reasons to Swap Your iPad for a Book at Bedtime
Reading can help you relax and prepare your body for a good night’s sleep. Mathew Walker, author of our Non-Fiction Book of the Month for January, Why We Sleep, explains why reading in print is best at bedtime.
Many of us are beyond tired. Why? What, precisely, about modernity has so perverted our otherwise instinctual sleep patterns, eroded our freedom to sleep, and thwarted our ability to do so soundly across the night? For those of us who do not have a sleep disorder, the reasons underlying this state of sleep deficiency can seem hard to pinpoint.
Beyond longer commute times and “sleep procrastination” caused by late-evening television and digital entertainment—both of which are not unimportant in their top-and-tail snipping of our sleep time—one of the five key societally engineered forces that has powerfully changed how much and how well we sleep is constant electric light.
We are a dark deprived society. Before Thomas Edison, and before gas and oil lamps, the setting sun would take with it the full stream of daylight from our eyes. The loss of daylight informs our suprachiasmatic nucleus (the brain’s twenty-four-hour clock) that nighttime is now in session; time to release the brake pedal on our pineal gland, allowing it to unleash vast quantities of melatonin that signal to our brains and bodies that it is time for bed. Appropriately scheduled tiredness, followed by sleep, would normally occur several hours after dusk across our human collective, somewhere between eight and ten p.m., just as we observe in hunter-gatherer tribes.
Electric light put an end to this natural order of things. It redefined the meaning of midnight for generations thereafter. Artificial evening light, even that of modest strength, or lux, will fool your suprachiasmatic nucleus into believing the sun has not yet set. The brake on melatonin, which should otherwise have been released with the timing of dusk, remains forcefully applied within your brain under duress of electric light.
One hundred years post-Edison, we now understand the biological mechanisms by which the electric lightbulbs managed to veto our natural timing and quality of sleep. The visible light spectrum—that which our eyes can see—runs the gamut from shorter wavelengths (approximately 380 nanometers) that we perceive as cooler violets and blues, to the longer wavelengths (around 700 nanometers) that we sense as warmer yellows and reds. Sunlight contains a powerful blend of all of these colors, and those in between (as the iconic Pink Floyd album cover of Dark Side of the Moon illuminates [so to speak]).
Sleep in modern humans is delayed from taking off the evening runway, usually by two to three hours each evening, on average. Artificial evening and nighttime light can therefore masquerade as sleep-onset insomnia—the inability to begin sleeping soon after getting into bed.
Just when things looked as bad as they could get for the suprachiasmatic nucleus with incandescent lamps, a new invention in 1997 made the situation far worse: blue light–emitting diodes, or blue LEDs. For this invention, Shuji Nakamura, Isamu Akasaki, and Hiroshi Amano won the Nobel Prize in physics in 2014. It was a remarkable achievement. Blue LED lights offer considerable advantages over incandescent lamps in terms of lower energy demands and, for the lights themselves, longer life spans. But they may be inadvertently shortening our own.
The light receptors in the eye that communicate “daytime” to the suprachiasmatic nucleus are most sensitive to short-wavelength light within the blue spectrum—the exact sweet spot where blue LEDs are most powerful. As a consequence, evening blue LED light has twice the harmful impact on nighttime melatonin suppression than the warm, yellow light from old incandescent bulbs, even when their lux intensities are matched. Of course, few of us stare headlong into the glare of an LED lamp each evening. But we do stare at LED-powered laptop screens, smartphones, and tablets each night, sometimes for many hours, often with these devices just feet or even inches away from our retinas. It has a very real impact on your melatonin release, and thus ability to time the onset of sleep.
One of the earliest studies found that using an iPad—an electronic tablet enriched with blue LED light—for two hours prior to bed blocked the otherwise rising levels of melatonin by a significant 23 percent. A more recent report took the story several concerning steps further. Healthy adults lived for a two-week period in a tightly controlled laboratory environment. The two-week period was split in half, containing two different experimental arms that everyone passed through: (1) five nights of reading a book on an iPad for several hours before bed (no other iPad uses, such as email or Internet, were allowed), and (2) five nights of reading a printed paper book for several hours before bed, with the two conditions randomized in terms of which the participants experienced as first or second.
Compared to reading a printed book, reading on an iPad suppressed melatonin release by over 50 percent at night. Indeed, iPad reading delayed the rise of melatonin by up to three hours, relative to the natural rise in these same individuals when reading a printed book. When reading on the iPad, their melatonin peak, and thus instruction to sleep, did not occur until the early-morning hours, rather than before midnight. Unsurprisingly, individuals took longer to fall asleep after iPad reading relative to print-copy reading.
But did reading on the iPad actually change sleep quantity/quality above and beyond the timing of melatonin? It did, in three concerning ways. First, individuals lost significant amounts of REM sleep following iPad reading. Second, the research subjects felt less rested and sleepier throughout the day following iPad use at night. Third was a lingering aftereffect, with participants suffering a ninety-minute lag in their evening rising melatonin levels for several days after iPad use ceased— almost like a digital hangover effect.
LED devices at night impacts our natural sleep rhythms, the quality of our sleep, and how alert we feel during the day. Due to its omnipresence, solutions for limiting exposure to artificial evening light are challenging. A good start is to create lowered, dim light in the rooms where you spend your evening hours. Avoid powerful overhead lights. Try turning off half of the lights in your home in the last 2 hours before bed can make a real difference. Mood lighting, or should I say, melatonin-encouraging lighting, is the order of the night. Maintaining complete darkness throughout the night is equally critical, the easiest fix for which comes from blackout curtains. Finally, you can install software on your computers, phones, and tablet devices that gradually de-saturate the harmful blue LED light as evening progresses.
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