5 reasons you can’t sleep

We face many obstacles in our search for shut-eye, from bad beds to faulty genes. Fortunately, wrapping our heads around what keeps us awake can help us catch those z’s.

DESPITE OUR NEAR-CONSTANT WORRYING over restlessness, Americans log about the same amount of sleep today as they did 50 years ago. But that doesn’t mean we’re snoozing enough. Approximately one in three US adults isn’t getting the seven or more daily hours of shut-eye recommended by the Centers for Disease Control and Prevention, according to a 2020 poll from the National Sleep Foundation. And even among those who log good rest at least six nights a week, one-quarter say drowsiness still regularly interferes with daily life.

That’s a lot of time lost to lethargy, but the consequences of chronic sleeplessness can be even more serious. Those who average less than six hours an evening have an increased risk of accidents, cardiovascular disease, and diabetes. Yet our quest for slumber meets so many intersecting obstacles, from the glow of screens down to our DNA.

Like a fast-fading dream, the full scope of the problem is difficult to comprehend. Decades of research has homed in on five key challenges we face in our race to REM. Understanding the factors that keep us from dozing off might mean lulling ourselves into peaceful repose in spite of the struggle.

Coffee mug, sun, clock, book, smartphone, head
Coffee can fill your natural flow of melatonin. Illustration: Raul Urias

Life gets in the way

In 1964, midwife Josiane Laures and furniture maker Antoine Senni volunteered for a NASA study on the effects of isolation intended to inform future space missions. That December, they descended into caves, a few hundred yards from each other, and stayed inside for as long as they could stand it. When the two emerged—Laures after 88 days and Senni after 126—their guesses about how much time had passed were off by weeks, and their sleep schedules were seriously disturbed. Senni, for example, could easily snooze for 30 hours at a stretch.

Like those of all humans, Laures’ and Senni’s bodies ran according to the circadian rhythm, an innate clock regulated by the brain and built to respond to the sun. At daybreak, those celestial rays signal the body to produce more of the hormone cortisol, which helps wake us up and get us moving. As light recedes, glands shift to manufacturing melatonin, the chemical that sets us on a path toward hitting the sack. But shielded from sunlight by the jagged cavities of the French Alps, Laures’ and Senni’s internal timekeepers grew untethered from the environment. In the absence of such stimuli, researchers have found that humans can slip into sleep-wake cycles that stretch as long as 48 hours.

Few people will ever live like Laures and Senni—even for a short time. But many modern habits can similarly disrupt our evolutionary rhythms in subtle ways. Devices like smartphones, computers, and LED bulbs emit “blue light,” a high-energy wavelength that can shut down the melatonin factory and send your inner timepiece spinning. Instead of sleeping, your brain is dazzled into thinking it’s time to get peppy. In one early trial, published in 2015 in Proceedings of the National Academy of Sciences, researchers found that people who read an e-book on an iPad before bed took longer to drift off, showed lower levels of melatonin, experienced less and later REM sleep, and had less alertness the next morning than those who read a print book.

Our morning routines also curb our z’s. When we wake up tired or feel sluggish midday, we tend to reach for coffee. Those beans can offer a temporary reprieve from grogginess (caffeine stimulates the central nervous system), but they also make it harder to drift off that night (it suppresses the production of melatonin and binds to receptors for adenosine, a neurotransmitter that helps to initiate z’s). In one study in Journal of Clinical Sleep Medicine, consuming the equivalent of a grande dark roast from Starbucks a full six hours before bed reduced sleep time by more than an hour.

Sitting all day doesn’t help either. Regular exercise can make it easier to go to bed, and deepen what rest you get. Working out elevates your core temperature, which signals to your body to stay awake; when it begins to fall, between 30 and 90 minutes after you hit the gym, you may start to feel sleepy. Unfortunately, 80 percent of Americans don’t get enough activity, defined by the US Department of Health and Human Services as at least 2.5 hours of moderate exercise a week—a goal that became harder to achieve when many shifted to at-home work in COVID-19 lockdown.

Skeleton, heartbeat, DNA, temperature graph
Temperature control at night is more of a challenge with climate change. Illustration: Raul Urias

The whole world is uncomfy

People’s preferred sleep environments vary widely. In a 2007 interview, Mariah Carey said she needed 15 hours of beauty rest surrounded by 20 humidifiers to lubricate her vocal cords, while elite swimmer Michael Phelps used to retire to a pressurized chamber designed to mimic an altitude of 9,000 feet to force his blood to absorb more oxygen in the hopes of speeding up his workout recovery.

Few people have the peculiar needs of a Grammy-winning recording artist or an Olympian, but achieving comfort is an essential part of shut-eye—and it’s only getting harder. Cozy bedding, a great pillow, sufficient darkness, and limited or masked disruptive noise (whether it’s your partner’s snoring or the sounds of the city) are simple enough. The bigger challenge comes from temperature: The air should be adequately cool, somewhere between 60ºF and 67ºF. Otherwise, it may interfere with your body’s natural self-refrigeration, which pushes your core and brain temperatures down at night in an effort to slow metabolic processes and save energy.

In the United States, hitting that Goldilocks temp is increasingly difficult. In one 2017 paper, four researchers in neuroscience, psychology, and political science teamed up to demonstrate the connection between climate change and slumber—or the lack of it. Between 2002 and 2011, as average nighttime temperatures rose, survey participants reported more nights of insufficient sleep. Projecting that data forward, the scientists predict that people in the US will collectively lose 23.8 million nights of shut-eye each month by 2050.

Even with their pillows plumped and the air conditioner on full blast, many people still struggle to recline. About 50 million Americans experience chronic pain, and roughly one-quarter of those also have a diagnosed sleep disorder, according to a 2015 poll by the National Sleep Foundation. For these would-be slumberers, discomfort leads to tossing, turning, and wakefulness. This disrupts restful repose—where your eyes stop moving and your brain waves slow down—and over time contributes to fatigue, which leads to more pain.

For these fitful hibernators, doctors don’t recommend the Carey method or the Phelps plan. Rather, they encourage everyone to establish a regular nighttime routine. Clinical trials suggest that meditation is worth a shot: It helps activate alpha brain waves, which are most abundant when we rest.

Body and facial structure
The repercussions of clinical insomnia are felt in all parts of the body. Illustration: Raul Urias

We’ve got the wrong genes

In 2011, Sonia Vallabh, a 27-year-old lawyer, got the results of a genetic test: She had a mutation in her PRNP gene that would likely result in fatal familial insomnia, a rare condition that had killed her mother. It stems from prions, or improperly folded proteins, which multiply and congregate in the thalamus, a part of the brain that regulates rest. The disease is almost always deadly; without sleep, the heart and blood vessels can’t repair themselves, the cerebrospinal fluid can’t dispose of waste, and the immune system is unable to recalibrate, which rapidly wears down the body.

Vallabh and her husband decided to re-career. Now they’re laboratory scientists working on developing drugs for fatal familial insomnia and other prion diseases, such as Creutzfeldt-Jakob, which causes rapid dementia and death, and Gerstmann-Straussler-Scheinker, which can progress to a fatal coma. While only a few dozen families in the world are known to carry the same mutation as Vallabh’s, a growing body of evidence suggests that many of us may have some amount of wakefulness coded into our DNA.

In 2019, a paper in the journal Nature Communications cross-referenced genomic data from 85,670 people with their activity logs from wearable motion sensors. In those with chronic insomnia, the researchers noted that certain gene splices—found in skeletal muscles, adrenal glands, and multiple brain regions—were more active than in people with “normal” nocturnal cycles.

One gene, known as PDE11A, stood out. In addition to that code’s established role in depression and Cushing’s disease, which causes the body to overproduce the stress hormone cortisol, the new data suggests a splice in people with insomnia can lessen the duration and quality of sleep.

For those with ongoing bedtime troubles, doctors often recommend polysomnography, or a sleep study—whereby a suite of machines monitor brain waves, eye movements, heart rate, breathing pattern, blood oxygen level, and general movement. With this data, they can identify which, if any, of the more than 80 kinds of sleep disorders—from ones that can be written into our genes, like restless leg syndrome, to narcolepsy—is getting between the patient and repose.

Headache, split personality, cigarette
Genetic conditions and poor mental health often set the stage for difficult sleep habits. Illustration: Raul Urias

Our minds are ill at ease

In the 1930s, researchers at the University of Georgia decided to deprive 17 students of sleep for 100 hours to document the psychological and physical fallout of prolonged wakefulness. The subjects became confused, had trouble reading, and reported visual disturbances. Some had backaches and difficulty distinguishing hot and cold temperatures by touch. On the last day of the experiment, one participant swung wildly between depression and euphoria.

Even shorter periods of wakefulness than this can manage to unsettle the mind, and the connection between sleep and mental health goes both ways. Conditions like depression, anxiety, trauma, bipolar disorder, and ADHD all have the potential to make real rest elusive.

Consider major depressive disorder, one of the most common mental illnesses, affecting some 16 million adult Americans and the leading cause of disability among the younger working population in the US. Almost everyone who experiences it also has some kind of bedtime disturbance. About 75 percent of patients report insomnia, which prevents them from falling and staying asleep, while others instead have hypersomnia, which leaves them feeling lethargic no matter how much time they spend in bed. Many people bounce back and forth between the two extremes during their depressive episodes.

It’s been nearly a century since that University of Georgia study, and doctors still aren’t certain why sleep and mental health are so connected. But they’re making progress. A group of papers published in 2019 in Nature Genetics linked poor snooze control to genetic mutations. And researchers have long tied some of the same snips found in insomniacs to the neurotransmitter dopamine, low levels of which can contribute to both depression and disordered sleep.

While there’s much to learn, small changes can help. Cutting stimulants like nicotine and caffeine, which arouse the central nervous system, can make sleep more accessible. So too can eliminating the “nightcap”; while alcohol makes you fall asleep faster, a 2013 meta-analysis of 20 studies found that moderate to heavy amounts interrupt restorative REM sleep and reduce the time spent in this stage overall. The more you drink, the more noticeable the effects become.

Smartwatch, book, headache
Sleep accessories can sometimes hurt more than they help. Illustration: Raul Urias

Wishing doesn’t make it so

Taken together, must-have products like weighted blankets, prescription sleeping aids, and meditation apps turned the need to wrangle our natural cycles into an $80 billion global industry in 2020. Yet our sleep isn’t improving.

The problem may lie in our obsession itself: We want rest so badly that it won’t come to us. In one classic study, researchers at the University of Oxford in England divided insomniacs into three groups, giving the first two sets different instructions on how to sleep while the final cohort received no direction. The results, published in 2002, suggest that counting sheep did not have the desired effect, and instead kept people awake slightly longer than imagining a chill scenario of their choosing, such as a trip to the beach or a picturesque walk to a waterfall. The researchers theorized that tabulating farm animals was simply too boring to override anxiety due to the task at hand.

Our tendency to overthink bedtime is driving sleeplessness to new heights. The more we track our rest, the more it seems to elude us. In 2017, researchers at Northwestern University and Rush University Medical School named this phenomenon “orthosomnia”—the desire for perfect sleep and the use of wearables to achieve it. In one of their three case studies, the authors described a man who came into the lab because he had linked symptoms like irritability and poor attention to nights when his fitness tracker reported suboptimal slumber. He fretted over hitting the 8-hour mark, though he averaged just 15 minutes less. The researchers suggested therapy and lifestyle changes to manage that stress, but the patient was skeptical—and never followed up. While data collection can be helpful, the experts concluded, fixating on the wrong metrics can keep us from accepting simple solutions.

This story originally ran in the Spring 2021 Calm issue of PopSci. Read more PopSci+ stories.

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Eleanor Cummins


Eleanor Cummins is a freelance science journalist writing about death, disaster, and bowling balls. Between 2017 and 2019 she worked at Popular Science, where she worked her way up from intern to assistant editor. She is an adjunct professor in New York University’s Science, Health, and Environmental Reporting Program.