Innumerable studies have documented the ill effects of insufficient sleep, defined as getting less sleep than we need to be our best. Beyond the tiredness, fogginess, and grumpiness we commonly note the next day, less-than-optimum sleep impairs focus, judgment, problem solving, and memory. An international survey of elementary students confirmed what sleep scientists have predicted for years: on average, pupils who got sufficient sleep before taking their exams did better, regardless of what kind of preparation they had received.

Insufficient sleep slows thinking and reaction times, increasing the chance of accidents. It lowers tolerance for frustration and heightens interpersonal sensitivity, making us more likely to fly off the handle over small slights, which may explain why children who do not get enough sleep are often misdiagnosed with attention deficit hyperactivity disorder (ADHD).

Early studies of insufficient sleep focused on these cognitive and behavioral effects. However, research conducted since the turn of the century has made it increasingly clear that sleep loss affects our bodies as much as our brains. In 1999, Karine Speigel at the University of Brussels and Eve Van Cauter at the University of Chicago published a landmark study demonstrating that partial sleep deprivation (four hours of sleep for two nights) increased cortisol levels and reduced glucose tolerance.

Subsequent research indicated that sleep loss (four hours for six nights) altered the levels of hormones that regulate hunger, causing an increase in appetite and a preference for calorie-dense, high-carbohydrate foods, including sweets, salty snacks, and starchy foods. Think of what you eat when you have to pull an all-nighter. Pizza? Coffee and doughnuts? I lived on brownies when I was caring for my dying father.

What Constitutes Enough Sleep?

If insufficient sleep can cause such serious problems, what constitutes enough sleep? Over the years, experts have offered a variety of answers and reasons for the hours we require, often generalizing from common practice or personal observation, like the English proverb that recommends “six hours’ sleep for a man, seven for a woman, and eight for a fool. ” Now sleep scientists are more circumspect, offering ranges to accommodate individual variation.

At present, the Centers for Disease Control and Prevention (CDC) recommend that adolescents get eight and a half hours and adults get seven to nine, based on studies of how they perform the next day. However, longevity studies reveal that people who sleep more than seven and a half hours don’t live as long as those who sleep only seven hours.

Some authorities avoid the numbers trap by suggesting that if you can wake up without an alarm clock, you are getting enough sleep. However, their advice does not consider the fact that many people keep work and school schedules that do not jibe with their internal sleep-wake cycles, requiring the use of alarm clocks.

Others say that if you do not get sleepy during the day, then you are probably getting enough sleep; however, the vast majority of North Americans and Europeans consume caffeinated drinks by day, so most are unable to tell if drowsiness is around the corner. To complicate matters, researchers have also discovered that a small percentage of people are long sleepers requiring nine hours, or short sleepers, who need only four or five to function well. Much as we might like clear guidelines, we may have to rely on our own experiences to arrive at what works best for us as individuals.

Quality vs. Quantity

While the quantity of sleep we get is clearly important, the quality is just as necessary to our physical, mental, and emotional well-being. Poor or fragmented sleep, which involves numerous imperceptible arousals that reduce restorative *SW sleep, typically leave people feeling just as tired in the morning as when they went to bed, and it results in the same cognitive, behavioral, and metabolic problems seen with sleep deprivation.

[*SW or Slow Wave sleep is a deep slumber that is characterized by slow, high-amplitude, synchronized brain waves. It appears to be the most restorative form of sleep. It is hard to wake people from SW sleep, and even when successful, they usually remain groggy (and grumpy!) for some time. ]

It is estimated that up to one-third of adults experience fragmented sleep. The most common causes are disrupted breathing (especially asthma and apnea), restless legs, depression, and aging, though environmental stimuli and autonomic arousal are also implicated.

Many of the symptoms associated with aging, from memory loss to wrinkled skin, can be attributed to reductions in SW sleep that accompany fragmented sleep. I used to wonder, as a child, why “old people” were always asking each other how they slept; now I know.

When we add caffeine to the mix, the task of defining adequate quantity and quality of sleep becomes even more complicated. Coffee is my drug of choice because it boosts my confidence. It does so by increasing levels of dopamine, enhancing pleasure, alertness, and drive—just what we need to be successful in the contemporary global economy. However, it also blocks the ability of adenosine to slow us down with fatigue and drowsiness after long hours of waking activity, masking our tiredness. Neurons fire more rather than less, prompting the pituitary gland to trigger the release of adrenaline, the fight-or-flight hormone. Adrenaline speeds up our heart rates, slows digestion, and tightens muscles to prepare for the emergency.

After six or seven hours, when the caffeine wears off, we feel exhausted and depressed, which leads us to . . . yet another cup. Over time, we sleep less, and less deeply, forgoing many of the restorative functions of our nightly slumber.

Sleep Deprivation Impairs Judgment

While some people do better than others on short sleep, those who believe they do great on four or five hours usually do not. They just think so because sleep deprivation impairs judgment. These facts alone make me want to ask presidential candidates how they sleep. In December 2008, when CNN anchor Anjali Rao asked former president Bill Clinton if he had any advice for incoming President Obama, he answered: “In my long political career, most of the mistakes I made, I made when I was too tired, because I tried too hard and worked too hard. You make better decisions when you’re not too tired. ”

©2014 Kat Duff. Reprinted with permission
from Atria Books/Beyond Words Publishing.
All Rights Reserved. www.beyondword.com

This article was adapted with permission from the book:

The Secret Life of Sleep
by Kat Duff.

The Secret Life of Sleep taps into the enormous reservoir of human experiences to illuminate the complexities of a world where sleep has become a dwindling resource. With a sense of infectious curiosity, award winning author Kat Duff mixes cutting-edge research with insightful narratives, surpris­ing insights, and timely questions to help us better understand what we’re losing before it’s too late.

Click here for more info and/or to order this book on Amazon.

About the Author

Kat Duff is the award-winning author of The Alchemy of Illness. She received her BA from Hampshire College where she pursued a multi-disciplinary concentration in literature, psychology, sociology, anthropology, and neuroscience. Kat’s life-long love of sleep and her friendship with two chronic insomniacs led her to investigate the subject of sleep with her signature multi-disciplinary approach. Visit her website at www.thesecretlifeofsleep.com/

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