October 14, 2015

Light: Sleep’s Greatest Enemy

A recent article in The New York Times posed a question we ask more than we’d like: Why Can’t We Fall Asleep? 

Author Maria Konnikova begins by explaining what happens when we DO fall asleep:
  • Body temperature falls (though hands and feet warm up).
  • Circadian clocks synchronize.
  • Melatonin (the hormone that sets our sleep/wake cycles) flows through the body.
  • The brain quiets.
  • Blood pressure falls.
  • Pulse rate slows.
  • Breathing evens out.
Finally, sleep.

Not surprisingly, some of the world’s leading sleep experts report disturbing statistics:
  • We now sleep an hour and a half LESS than we did on work nights half a century ago. It used to be eight and a half hours; now it’s under seven.
  • 31% of us sleep less than six hours a night.
  • 69% report not getting enough sleep.
  • Between 1905 and 2008, children have lost about a minute of sleep each year.
Adults… children… this pattern of reduced sleep applies to everyone.

It’s not that we’re just getting up earlier. According to Elizabeth Klerman, head of the Analytic and Modeling Unit in the Sleep and Circadian Disorders division at Boston’s Harvard-affiliated Brigham and Women’s Hospital, “When you go to bed affects how long you can sleep, no matter how tired you are.”

When bedtimes vary significantly from one night to another, normal and important circadian cycles become disrupted. Production of melatonin gets fouled up; key melatonin receptors don't function properly.

Sleep Hygiene Matters
Then there’s the important element of sleep “hygiene.”

What helps? Exercise and regular mealtimes. Yes, once again, we see the key role of diet and exercise.

What doesn’t help? Another familiar list:
  • Nicotine
  • Caffeine
  • Alcohol
  • Being overweight
Light, the Biggest Culprit
Most likely, light has the biggest negative impact on our sleep.

For countless millennia, humans could rely on limited sources of light: the sun, the moon, the cooking fire at night. We evolved with exquisite life-supporting sensitivities to light… sensitivities that helped us remain keenly awake during the day and healthfully asleep at night.

Over the past century, everything has changed.

It’s not just the light bulb. More and more, the culprit is “blue light,” the short-wave variety that comes at us, all the time, from a host of relatively new sources:
  • Televisions
  • Computers
  • Phones
  • E-readers
Blue light “filters” now exist for most electronic devices, but their effectiveness and use are, so far, limited.

Blue Light as Daylight
Ninety percent of all Americans now use electronic devices that emit interfering blue light. Our brains interpret this new blue light as daylight, and thus postpone the signals that induce sleepiness. According to the NYT article, “When ‘dusk’ gets pushed progressively later because of these false light cues, we get a surge of energy rather than the intended melatonin release.”

Harvard circadian neuroscientist Steven Lockley conducted a simple experiment. He had subjects read from either a printed book or a light-emitting e-book about four hours before bedtime for five consecutive evenings. Results were immediate and profound. As the NYT article reported:
Those who’d read an e-book released less melatonin and were less sleepy than those who’d read a regular book; their melatonin release was delayed by more than an hour and a half, and their circadian clocks were time-shifted. It took them longer to fall asleep. The next morning, they were less alert. These resetting effects can result not just from prolonged reading but from a single exposure.

 One Light – Eight Years of Insomnia
I'm well aware of how light can cause insomnia. My longest and worst spell of insomnia occurred when I was in my 60s, and it lasted about eight years. During that time, whenever I tried sleeping in my bedroom, my body would jerk just as I started to doze off, and I'd be awake until 4am or later. I finally discovered that I could get a good night's sleep if I bedded down on the living room couch. Every time I tried to return to the bedroom, the body-jerk insomnia recurred.

It finally occurred to me (d'uh!) that I had no trouble taking my afternoon nap in the bedroom. That led me to wonder if the nighttime culprit might be the streetlight on the other side of the road from my bedroom windows. I installed blackout curtains to replace the Venetian blinds and... Guess what? The body jerking stopped and I could sleep in the bedroom again. Yeah

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