You may not know how tired you are

We all yearn for rest. But the gravest danger is not the impact of sleep deprivation -- but the simple fact that we no longer realise how tired we are.

By Mark Wolverton

Published: Fri 12 Jun 2015, 10:04 PM

Last updated: Wed 8 Jul 2015, 3:15 PM

A 2011 CDC analysis found that over 35 percent of adults routinely get less than seven hours of shuteye nightly. There’s no magic number for the perfect amount of sleep, but research suggests that most of us require more—about eight hours—to perform optimally. (Still, a small percentage of people experience no adverse effects on performance with just five hours.) Unfortunately, societal exigencies such as overstuffed work schedules, family stress, and our constantly pinging smart phones conspire against our getting enough sleep.

Our need for sleep “is fairly inflexible, yet modern social and economic systems provoke it constantly,”contends David Dinges, who heads the Sleep and Chronobiology laboratory at the University of Pennsylvania. Rest is too often treated as a disposable option: “It’s a badge of courage to stay up all night to get the job done--we celebrate that in our society,” says Mark R. Rosekind, who studies issues of fatigue and safety at the NTSB.

As a result, everyday sleep deprivation causes cognitive impairments that lead to minor and major disasters in nearly every occupation: truckers falling asleep on highways, doctors making errors in treatment, nuclear power plant operators missing alarms. New research reveals that sleep loss affects the body on a systemic level as well, creating metabolic and immune disruptions that can cause obesity, heart disease, reduced fertility—even cancer.

Fortunately, while studies increasingly underscore the problematic nature of our national sleep debt, a new science of sleep suggests critical steps we can take as individuals and a society to achieve that elusive, all-important shut-eye.


For over a decade, insufficient sleep has been well established as a health-risk factor: A seminal 2002 study revealed a strong relationship between an individual’s reported sleep and mortality.

“People who slept less than seven hours a night—or more than nine--were at increased risk for all-cause mortality,” says University of Pittsburgh psychiatrist Martica Hall. Other studies revealed a similar curvilinear relationship between sleep duration and conditions such as cardiovascular disease and obesity, although it remains relatively unclear just how disturbed sleep affects our health.

New research suggests that the answer is connected to the functioning of our circadian clock, which evolved to follow the roughly 24-hour light-and-dark cycle of the Earth’s daily rotation. The existence of the body’s “master clock,” the suprachiasmatic nucleus (SCN) located in the hypothalamus, has been known for decades.

But only recently have molecular biology and genetics yielded the startling finding that “circadian regulation exists in every cell of the body--the liver, the kidneys, even skin fibroblasts,” Dinges says. “It’s coordinated and entrained internally, and then entrains to the outside world.”

Some researchers compare the system to an orchestra, in which the SCN is the conductor and the other body clocks are the players. The clocks operate all the way down to the genetic level.


Night by sleepless night, we undermine our cognitive functioning, yet the true extent of our cognitive shortcoming goes largely undetected--except by the scientists who study sleep loss.

In 2003, a team including Dinges, lead by his then colleague at Penn, Hans Van Dongen, conducted a major experiment in which participants were divided into three separate groups: one that slept four hours a night, one for six hours, and a control group for eight hours. The study went on for two weeks and each day participants were repeatedly given a memory test and a psychomotor vigilance task, a simple computer-based assessment of attentiveness and response.

Developed by Dinges, the PVT is simplicity itself: Subjects sit for 10 minutes in front of a screen, hitting a button whenever a bright spot appears; meanwhile. reaction times and other sleepiness indicators (such as droopy eyelids) are monitored. The test measures precisely the sort of cognitive and physiological abilities that insufficient sleep dulls or eliminates. A mere half-second delay in response indicates a lapse of wakefulness--or as researchers term it, “microsleep.”

As might be expected, eight-hour sleepers showed no impairment of functioning on the tests. But those getting less sleep did—and performance declined steadily over time, even though participants were getting consistent, if limited, sleep each night.


For modern Americans, the type of work we do--and the increasing hours we’ve spent doing it since the recession began--is a major reason we’re not getting the sleep we need. While some occupations are associated with more sleep loss than others, none is exempt. A recent CDC report noted that about 27 percent of people in the financial and insurance businesses are sleep-deprived, with the figure rising to 42 percent among mine workers. “The challenges of schedules cut across many occupations and industries,” confirms Roger Rosa, a researcher at the National Institute for Occupational Safety and Health. Still, he observes, “certain ones seem to be more prone to demanding work schedules.”

He singles out manufacturing, which uses a lot of shift work schedules, and anything involving continuous processes, like oil refineries. He also notes that sleep loss is a frequent problem for people in seasonal industries, such as construction. “It’s not only night versus day work, it could be long hours that people experience, trying to meet deadlines or take advantage of weather or things like that,” he says. “Emergency response is another example where often what needs to get done will take a lot of staff working many hours.”

Another career notorious for chronic sleep deprivation is medicine, particularly during residency, when fledgling doctors routinely work up to 28-hour shifts.


Even if we can’t fully overcome the effects of not getting enough shut-eye, it’s possible to balance our biology with the demands of our society. The first step is to admit that sleep loss is a problem that must be faced individually and culturally.

Fortunately, there are signs that attitudes about sleep’s importance are changing. Commercial airline rules now require a 10-hour minimum rest period for pilots prior to flight duty—and mandate pilots be given the opportunity to sleep uninterrupted for eight of those hours.) Similarly, 2011 ushered in revised regulations for medical residents, limiting first-year residents to 16-hour shifts prior to an eight-hour break. Second- and third-year residents may still work up to 28-hour shifts,

The shifting cultural tide may also aid an important group of workers who need to stay alert for long, unpredictable hours under significant amounts of stress: soldiers in combat. Modern warfare and technology have heightened the effects of sleeplessness in the military. Researchers Thomas Balkin, Sharon McBride, and Nancy Wesensten of Walter Reed are currently developing an alertness/performance management system, which includes a wrist actigraph device that monitors the wearer’s movements with an accelerometer and displays information on recent sleep history and its implications.


Although the problem of sleep deprivation cuts across all occupations, it’s a particular concern for those who work the night shift. “Humans evolved in a world where there wasn’t electricity to make shift work possible. We’re forcing people to live under conditions that we’re not suited for,” says Charmane Eastman, director of the biological rhythms research laboratory at Rush University Medical Center. “Even when workers use melatonin or sleeping pills to sleep during the day, they’re still going to become sleepy at night because their circadian clock says, ‘Okay, it’s night.’”

Contrary to popular belief, melatonin isn’t required for sleep, though it definitely has a sedative effect. Eastman explains: “It’s the way the internal circadian clock tells the body what time it is. Melatonin is the ‘dark signal.’” Through careful adjustment of light exposure (the main signal that the SCN uses to “set” the body’s internal clock by controlling the flow of melatonin from the pineal gland) and sometimes administering extra melatonin with pills, Eastman has demonstrated that it’s possible to phase-shift night workers’ circadian clock to a new rhythm--which can help them get the sleep they so critically need.

Strategies include exposing shift workers to controlled amounts of bright light with the use of light boxes at work, then limiting their light exposure after their shift by having them wear sunglasses on their commute home.


Often, the most difficult step toward improving your sleep is realizing that not sleeping enough is indeed a real problem. With some relatively simple shifts in habit, we can all help ourselves to get better rest.

For example, while you may have stopped keeping a regular bedtime decades ago when your mother stopped tucking you in, sticking to a sleep schedule—one in tune with your natural proclivity towards being a night owl or an early bird--in which you hit the sack at the same time each night, is important.

If you find that your schedule is at odds with your natural sleep preferences (say you must leave for work by 6 a.m. but don’t become sleepy until midnight) you can help prime your body to drift off on the earlier side by manipulating the sleep homeostat. Our bodies naturally experience a sharp drop in temperature at the onset of sleep, and you can recreate this process by taking a hot bath or shower just before you get into bed. As your body cools off afterward, it will help usher in a feeling of sleepiness.

Simply unplugging is also wise. The thought of leaving your laptop at the office or not checking your iPhone before bed might make you anxious, but limiting technology use after dark--particularly in the bedroom--is critical. “Just getting light from computer and other screens before bed can throw off your circadian cycles,” notes fatigue researcher Mark. R. Rosekind.

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