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At the same time, today's teens are maturing in an era of ubiquitous electronic media, and they are fervent participants. Some 92 percent of U.S. teens have smartphones, and 24 percent report being online "constantly," according to a 2015 report by the Pew Research Center. Teens have access to multiple electronic devices they use simultaneously, often at night. Some 72 percent bring cellphones into their bedrooms and use them when they are trying to go to sleep, and 28 percent leave their phones on while sleeping, only to be awakened at night by texts, calls or emails, according to a 2011 National Sleep Foundation poll on electronic use. In addition, some 64 percent use electronic music devices, 60 percent use laptops and 23 percent play video games in the hour before they went to sleep, the poll found. More than half reported texting in the hour before they went to sleep, and these media fans were less likely to report getting a good night's sleep and feeling refreshed in the morning. They were also more likely to drive when drowsy, the poll found.

The problem of sleep-phase delay is exacerbated when teens are exposed late at night to lit screens, which send a message via the retina to the portion of the brain that controls the body's circadian clock. The message: It's not nighttime yet.

Yuan, a clinical associate professor of pediatrics, said she routinely sees young patients in her clinic who fall asleep at night with cellphones in hand.

"With academic demands and extracurricular activities, the kids are going nonstop until they fall asleep exhausted at night. There is not an emphasis on the importance of sleep, as there is with nutrition and exercise," she said. "They say they are tired, but they don't realize they are actually sleep-deprived. And if you ask kids to remove an activity, they would rather not. They would rather give up sleep than an activity."

The role of parents

Adolescents are also entering a period in which they are striving for autonomy and want to make their own decisions, including when to go to sleep. But studies suggest adolescents do better in terms of mood and fatigue levels if parents set the bedtime - and choose a time that is realistic for the child's needs. According to a 2010 study published in the journal Sleep, children are more likely to be depressed and to entertain thoughts of suicide if a parent sets a late bedtime of midnight or beyond.

In families where parents set the time for sleep, the teens' happier, better-rested state "may be a sign of an organized family life, not simply a matter of bedtime," Carskadon said. "On the other hand, the growing child and growing teens still benefit from someone who will help set the structure for their lives. And they aren't good at making good decisions."

They say they are tired, but they don't realize they are actually sleep-deprived. And if you ask kids to remove an activity, they would rather not. They would rather give up sleep than an activity.

According to the 2011 sleep poll, by the time U.S. students reach their senior year in high school, they are sleeping an average of 6.9 hours a night, down from an average of 8.4 hours in the sixth grade. The poll included teens from across the country from diverse ethnic backgrounds.

American teens aren't the worst off when it comes to sleep, however; South Korean adolescents have that distinction, sleeping on average 4.9 hours a night, according to a 2012 study in Sleep by South Korean researchers. These Asian teens routinely begin school between 7 and 8:30 a.m., and most sign up for additional evening classes that may keep them up as late as midnight. South Korean adolescents also have relatively high suicide rates (10.7 per 100,000 a year), and the researchers speculate that chronic sleep deprivation is a contributor to this disturbing phenomenon.

By contrast, Australian teens are among those who do particularly well when it comes to sleep time, averaging about nine hours a night, possibly because schools there usually start later.

Regardless of where they live, most teens follow a pattern of sleeping less during the week and sleeping in on the weekends to compensate. But many accumulate such a backlog of sleep debt that they don't sufficiently recover on the weekend and still wake up fatigued when Monday comes around.

Moreover, the shifting sleep patterns on the weekend - late nights with friends, followed by late mornings in bed - are out of sync with their weekday rhythm. Carskadon refers to this as "social jet lag."

"Every day we teach our internal circadian timing system what time it is - is it day or night? - and if that message is substantially different every day, then the clock isn't able to set things appropriately in motion," she said. "In the last few years, we have learned there is a master clock in the brain, but there are other clocks in other organs, like liver or kidneys or lungs, so the master clock is the coxswain, trying to get everybody to work together to improve efficiency and health. So if the coxswain is changing the pace, all the crew become disorganized and don't function well."

This disrupted rhythm, as well as the shortage of sleep, can have far-reaching effects on adolescent health and well-being, she said.

"It certainly plays into learning and memory. It plays into appetite and metabolism and weight gain. It plays into mood and emotion, which are already heightened at that age. It also plays into risk behaviors - taking risks while driving, taking risks with substances, taking risks maybe with sexual activity. So the more we look outside, the more we're learning about the core role that sleep plays," Carskadon said.

Many studies show students who sleep less suffer academically, as chronic sleep loss impairs the ability to remember, concentrate, think abstractly and solve problems. In one of many studies on sleep and academic performance, Carskadon and her colleagues surveyed 3,000 high school students and found that those with higher grades reported sleeping more, going to bed earlier on school nights and sleeping in less on weekends than students who had lower grades.

Sleep is believed to reinforce learning and memory, with studies showing that people perform better on mental tasks when they are well-rested. "We hypothesize that when teens sleep, the brain is going through processes of consolidation - learning of experiences or making memories," Yuan said. "It's like your brain is filtering itself - consolidating the important things and filtering out those unimportant things." When the brain is deprived of that opportunity, cognitive function suffers, along with the capacity to learn.

"It impacts academic performance. It's harder to take tests and answer questions if you are sleep-deprived," she said.

That's why cramming, at the expense of sleep, is counterproductive, said Pelayo, who advises students: Don't lose sleep to study, or you'll lose out in the end.

The panic attack

Chloe Mauvais, 16, hit her breaking point at the end of a very challenging sophomore year when she reached "the depths of frustration and anxiety." After months of late nights spent studying to keep up with academic demands, she suffered a panic attack one evening at home.

"I sat in the living room in our house on the ground, crying and having horrible breathing problems," said the senior at Menlo-Atherton High School. "It was so scary. I think it was from the accumulated stress, the fear over my grades, the lack of sleep and the crushing sense of responsibility. High school is a very hard place to be."

We hypothesize that when teens sleep, the brain is going through processes of consolidation - learning of experiences or making memories. It's like your brain is filtering itself.

Where she once had good sleep habits, she had drifted into an unhealthy pattern of staying up late, sometimes until 3 a.m., researching and writing papers for her AP European history class and prepping for tests.

"I have difficulty remembering events of that year, and I think it's because I didn't get enough sleep," she said. "The lack of sleep rendered me emotionally useless. I couldn't address the stress because I had no coherent thoughts. I couldn't step back and have perspective. ... You could probably talk to any teen and find they reach their breaking point. You've pushed yourself so much and not slept enough and you just lose it."

The experience was a kind of wake-up call, as she recognized the need to return to a more balanced life and a better sleep pattern, she said. But for some teens, this toxic mix of sleep deprivation, stress and anxiety, together with other external pressures, can tip their thinking toward dire solutions.

Research has shown that sleep problems among adolescents are a major risk factor for suicidal thoughts and death by suicide, which ranks as the third-leading cause of fatalities among 15- to 24-year-olds. And this link between sleep and suicidal thoughts remains strong, independent of whether the teen is depressed or has drug and alcohol issues, according to some studies.

"Sleep, especially deep sleep, is like a balm for the brain," said Shashank Joshi, MD, associate professor of psychiatry and behavioral sciences at Stanford. "The better your sleep, the more clearly you can think while awake, and it may enable you to seek help when a problem arises. You have your faculties with you. You may think, 'I have 16 things to do, but I know where to start.' Sleep deprivation can make it hard to remember what you need to do for your busy teen life. It takes away the support, the infrastructure."

Sleep is believed to help regulate emotions, and its deprivation is an underlying component of many mood disorders, such as anxiety, depression and bipolar disorder. For students who are prone to these disorders, better sleep can help serve as a buffer and help prevent a downhill slide, Joshi said.

Rebecca Bernert, PhD, who directs the Suicide Prevention Research Lab at Stanford, said sleep may affect the way in which teens process emotions. Her work with civilians and military veterans indicates that lack of sleep can make people more receptive to negative emotional information, which they might shrug off if they were fully rested, she said.

"Based on prior research, we have theorized that sleep disturbances may result in difficulty regulating emotional information, and this may lower the threshold for suicidal behaviors among at-risk individuals," said Bernert, an instructor of psychiatry and behavioral sciences. Now she's studying whether a brief nondrug treatment for insomnia reduces depression and risk for suicide.

Sleep deprivation also has been shown to lower inhibitions among both adults and teens. In the teen brain, the frontal lobe, which helps restrain impulsivity, isn't fully developed, so teens are naturally prone to impulsive behavior. "When you throw into the mix sleep deprivation, which can also be disinhibiting, mood problems and the normal impulsivity of adolescence, then you have a potentially dangerous situation," Joshi said.

Some schools shift

Given the health risks associated with sleep problems, school districts around the country have been looking at one issue over which they have some control: when school starts in the morning. The trend was set by the town of Edina, Minnesota, a well-to-do suburb of Minneapolis, which conducted a landmark experiment in student sleep in the late 1990s. It shifted the high school's start time from 7:20 a.m. to 8:30 a.m. and then asked University of Minnesota researchers to look at the impact of the change. The researchers found some surprising results: Students reported feeling less depressed and less sleepy during the day and more empowered to succeed. There was no comparable improvement in student well-being in surrounding school districts where start times remained the same.

With these findings in hand, the entire Minneapolis Public School District shifted start times for 57,000 students at all of its schools in 1997 and found similarly positive results. Attendance rates rose, and students reported getting an hour's more sleep each school night - or a total of five more hours of sleep a week - countering skeptics who argued that the students would respond by just going to bed later.

For the health and well-being of the nation, we should all be taking better care of our sleep, and we certainly should be taking better care of the sleep of our youth.

Other studies have reinforced the link between later start times and positive health benefits. One 2010 study at an independent high school in Rhode Island found that after delaying the start time by just 30 minutes, students slept more and showed significant improvements in alertness and mood. And a 2014 study in two counties in Virginia found that teens were much less likely to be involved in car crashes in a county where start times were later, compared with a county with an earlier start time.

Bolstered by the evidence, the American Academy of Pediatrics in 2014 issued a strong policy statement encouraging middle and high school districts across the country to start school no earlier than 8:30 a.m. to help preserve the health of the nation's youth. Some districts have heeded the call, though the decisions have been hugely contentious, as many consider school schedules sacrosanct and cite practical issues, such as bus schedules, as obstacles.

In Fairfax County, Virginia, it took a decade of debate before the school board voted in 2014 to push back the opening school bell for its 57,000 students. And in Palo Alto, where a recent cluster of suicides has caused much communitywide soul-searching, the district superintendent issued a decision in the spring, over the strenuous objections of some teachers, students and administrators, to eliminate "zero period" for academic classes - an optional period that begins at 7:20 a.m. and is generally offered for advanced studies.

Certainly, changing school start times is only part of the solution, experts say. More widespread education about sleep and more resources for students are needed. Parents and teachers need to trim back their expectations and minimize pressures that interfere with teen sleep. And there needs to be a cultural shift, including a move to discourage late-night use of electronic devices, to help youngsters gain much-needed rest.

"At some point, we are going to have to confront this as a society," Carskadon said. "For the health and well-being of the nation, we should all be taking better care of our sleep, and we certainly should be taking better care of the sleep of our youth."

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Among teens, sleep deprivation an epidemic

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Sleep deprivation increases the likelihood teens will suffer myriad negative consequences, including an inability to concentrate, poor grades, drowsy-driving incidents, anxiety, depression, thoughts of suicide and even suicide attempts.

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Richter , Ruthann. “Among Teens, Sleep Deprivation an Epidemic.” EHR National Symposium, 8 Oct. 2015, med.stanford.edu/news/all-news/2015/10/among-teens-sleep-deprivation-an-epidemic.html. Accessed 9 Oct. 2019.

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Percent of Teens who Text Instead of Sleep         1A              

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Percent of Teens who Text Instead of Sleep         1A              

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“Some 92 percent of U.S. teens have smartphones, and 24 percent report being online “constantly,” according to a 2015 report by the Pew Research Center. Teens have access to multiple electronic devices they use simultaneously, often at night. Some 72 percent bring cellphones into their bedrooms and use them when they are trying to go to sleep” (Richter).

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“I have difficulty remembering events of that year, and I think it’s because I didn’t get enough sleep,” she said. “The lack of sleep rendered me emotionally useless. I couldn’t address the stress because I had no coherent thoughts. I couldn’t step back and have perspective. … You could probably talk to any teen and find they reach their breaking point. You’ve pushed yourself so much and not slept enough and you just lose it.”

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When it comes to memory, sleep is a Goldilocks issue: both too much and too little aren't good. Aim for "just right," says a new report from the Harvard-based Nurses' Health Study.

"Our findings suggest that getting an 'average' amount of sleep, seven hours per day, may help maintain memory in later life and that clinical interventions based on sleep therapy should be examined for the prevention of [mental] impairment," said study leader Elizabeth Devore, an instructor in medicine at Harvard-affiliated Brigham and Women's Hospital in Boston, in a news release.

A group of women taking part in the Nurses' Health Study were asked about their sleep habits in 1986 and 2000, and were interviewed about memory and thinking skills three times over a later six-year period. Devore and her colleagues observed worse performance on brain testing among women who slept five hours or fewer per night or nine hours or more, compared with those getting seven to eight hours of sleep a night. Their findings were published online in the Journal of the American Geriatrics Society.

The researchers estimated that undersleepers and oversleepers were mentally two years older than the women who got seven to eight hours of shut-eye a night.

Beyond memory

Although this study couldn't prove that getting too little or too much sleep causes memory and thinking problems, it's in line with other work showing the potentially harmful effects of poor sleep. Previous research has linked poor sleep with higher risks of heart disease and stroke, type 2 diabetes, and depression.

How might sleep affect memory? People who are persistently sleep deprived are more likely to have high blood pressure, diabetes, and narrowed blood vessels. Each of these can decrease blood flow inside the brain. Brain cells need a lot of oxygen and sugar, so blood flow problems could affect their ability to work properly.

Poor sleep could affect the brain in another way. Sleep-deprived mice develop more deposits of a protein called beta amyloid in the brain compared with mice allowed to sleep normally. In humans, beta amyloid deposits in the brain are linked to declines in memory and thinking and also increase the risk of dementia.

What about people who sleep too much? People who spend more than nine or 10 hours a night in bed often have poor sleep quality. So for both too little and too much sleep, the important number may be the hours of quality sleep.

Another possibility is a two-way street between sleep and memory: sleep quality may affect memory and thinking, and the brain changes that cause memory and thinking problems may disturb sleep.

Getting better sleep

Here are 12 tips for getting better sleep:

Establish a regular bedtime and a relaxing bedtime routine-examples might include taking a warm bath or listening to soothing music.

Use your bed only for sleeping or lovemaking. Avoid reading and watching television in bed.

If you can't fall asleep after 15 to 20 minutes, get out of bed and go into another room. Do something relaxing, such as reading quietly with a dim light. Don't watch television or use a computer, since the light from their screens has an arousing effect. When you feel sleepy, get back into bed. Don't delay your scheduled wake-up time to make up for lost sleep.

Get plenty of exercise. Build up to 45 minutes of moderate exercise nearly every day. Get your exercise early in the day. Try some easy stretching exercises or yoga to relax your muscles and your mind at bedtime.

Whenever possible, schedule stressful or demanding tasks early in the day and less challenging activities later. This helps you wind down at the end of your day.

Don't go to bed hungry, but don't eat a big meal right before getting into bed. If you want a bedtime snack, keep it bland and light.

Limit caffeine and consume none after 2 p.m.

To decrease middle-of-the-night urination, don't drink any fluids after dinner.

Avoid alcohol after dinnertime. Although many people think of it as a sedative, it can get in the way of quality sleep.

Be sure your bed is comfortable and your bedroom is dark and quiet. Consider a sleep mask or earplugs.

Don't take long naps during the day. If you need a nap, restrict it to 20 to 30 minutes in the early afternoon.

Practice relaxation breathing. Use slow breaths, especially when you exhale.

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Too little sleep, and too much, affect memory - Harvard Health Blog

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When it comes to memory, sleep is a Goldilocks issue: both too much and too little aren't good. Aim for "just right," says a new report from the Harvard-based Nurses' Health Study.

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LeWine, Howard, and M.d. “Too Little Sleep, and Too Much,

Affect Memory.” Harvard Health Blog, Harvard Health Publishing, 30 Oct. 2015, www.health.harvard.edu/blog/little-sleep-much-affect-memory-201405027136. Accessed 9 Oct. 2019.

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“Devore and her colleagues observed worse performance on brain testing among women who slept five hours or fewer per night or nine hours or more, compared with those getting seven to eight hours of sleep a night” (LeWine).

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Stages of sleep

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© COPYRIGHT 2022 OneCare Media, LLC ALL RIGHTS RESERVED | PRIVACY | ADVERTISING DISCLOSURE | ACCESSIBILITY STATEMENT

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“Stages of Sleep - Non-REM and REM Sleep Cycles.” Tuck Sleep, 19

Dec. 2018, www.tuck.com/stages/. Accessed 9 Oct. 2019.

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Should you drink more coffee? Should you take melatonin? Can you train yourself to need less sleep? A physician's guide to sleep in a stressful age.

Mauricio Alejo

During residency, Iworked hospital shifts that could last 36 hours, without sleep, often without breaks of more than a few minutes. Even writing this now, it sounds to me like I'm bragging or laying claim to some fortitude of character. I can't think of another type of self-injury that might be similarly lauded, except maybe binge drinking. Technically the shifts were 30 hours, the mandatory limit imposed by the Accreditation Council for Graduate Medical Education, but we stayed longer because people kept getting sick. Being a doctor is supposed to be about putting other people's needs before your own. Our job was to power through.

The shifts usually felt shorter than they were, because they were so hectic. There was always a new patient in the emergency room who needed to be admitted, or a staff member on the eighth floor (which was full of late-stage terminally ill people) who needed me to fill out a death certificate. Sleep deprivation manifested as bouts of anger and despair mixed in with some euphoria, along with other sensations I've not had before or since. I remember once sitting with the family of a patient in critical condition, discussing an advance directive-the terms defining what the patient would want done were his heart to stop, which seemed likely to happen at any minute. Would he want to have chest compressions, electrical shocks, a breathing tube? In the middle of this, I had to look straight down at the chart in my lap, because I was laughing. This was the least funny scenario possible. I was experiencing a physical reaction unrelated to anything I knew to be happening in my mind. There is a type of seizure, called a gelastic seizure, during which the seizing person appears to be laughing-but I don't think that was it. I think it was plain old delirium. It was mortifying, though no one seemed to notice.

No matter what happened to my body, I never felt like it was dangerous for me to keep working. I knew I was irritable and sometimes terse, and I didn't smell the best, but I didn't think anything I did was unsafe. Sleep experts often liken sleep-deprived people to drunk drivers: They don't get behind the wheel thinking they're probably going to kill someone. But as with drunkenness, one of the first things we lose in sleep deprivation is self-awareness.
In a high-school science-fair experiment in 1964, a 17-year-old stayed awake for 11 days. Since then, standards for science-fair safety have changed.
It's this way of thinking-that you can power through, that sleep is the easiest corner to cut-that makes sleep disturbance among the most common sources of health problems in many countries. Insufficient sleep causes many chronic and acute medical conditions that have an enormous impact on quality of life, not to mention the economy. While no one knows why we sleep, it is a universal biological imperative; no animal with a brain can survive without it. Dolphins are said to sleep with only half their brain at a time, keeping partially alert for predators. Many of us spend much of our lives in a similar state.

Since my residency, I've become sort of obsessive about sleep-how much we really need, how to optimize it, whether there are ways to game the system. What can be said definitively about sleep and wakefulness? What I've found is a perpetual divide between what's known to scientists and what most people do.

How much sleep do I actually need?

One 2014 study of more than 3,000 people in Finland found that the amount of sleep that correlated with the fewest sick days was 7.63 hours a night for women and 7.76 hours for men. So either that is the amount of sleep that keeps people well, or that's the amount that makes them least likely to lie about being sick when they want to skip work. Or maybe people who were already sick with some chronic condition were sleeping more than that-or less-as a result of their illness. Statistics are tough to interpret. Isolated studies are tougher. That's why the American Academy of Sleep Medicine and the Sleep Research Society convened a body of scientists from around the world to answer this question through a review of known research. They looked at the effects of sleep on cardiovascular disease, cancer, obesity, cognitive failure, and human performance, vetting each paper based on its scientific strength.

The consensus: Most adults function best after seven to nine hours of sleep a night. Going to sleep and waking up at consistent times each day is valuable too. When we get fewer than seven hours, we're impaired (to degrees that vary from person to person). When sleep persistently falls below six hours per 24, we are at an increased risk of health problems.

Can I train myself to need less sleep?

As an experiment for his high-school science fair in 1964, a 17-year-old San Diego boy named Randy Gardner stayed awake for 264 hours. That is 11 days. Since 1964, the standards for science-fair safety have changed.

The project attracted the attention of the Stanford sleep researcher William Dement, among others. Dement and other researchers took turns watching and assessing the young man's consciousness. By all accounts, he took no stimulant medications. Nor did he seem to suffer any permanent deficits. Dement said that on day 10, Gardner even beat him at pinball. The boy later said of his experiment that the key to staying awake was "just talking yourself into it."

I asked David Dinges, the chief of the division of sleep and chronobiology at the University of Pennsylvania, how many people could do anything close to that without dying. He replied that "when animals are sleep-deprived constantly, they will suffer serious biological consequences. Death is one of those consequences."

That said, cases like Gardner's-of people who suffered great sleep deprivation without major setbacks-are well documented. A small number of people, sometimes called "short sleepers" and commonly thought to make up perhaps 1 percent of the population, seem to thrive on only four or five hours a night. Dinges said that "we probably do have people among us-and not necessarily 1 percent; there may be many more than that-who can actually tolerate sleep loss better than others." This proposition has been borne out in studies of participants in transoceanic sailing races, which did not afford them the luxury of long blocks of sleep. The winners tended to be the people who slept the least, often in multiple short bursts.

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The concept of sleeping in short bursts has spread since those races began, in the 1960s. Today, a small global community of people practices "polyphasic sleeping," based on the idea that by partitioning your sleep into segments, you can get away with less of it.

Though it is possible to train oneself to sleep in spurts instead of a single nightly block, Dinges says it does not seem possible to train oneself to need less sleep per 24-hour cycle. And he notes that even for the 1 percent (or so) who can survive on less sleep and function well cognitively, we still don't know how the practice might be affecting metabolism, mood, and myriad other factors. "You may be cheerful, but not cognitively fit. Or you may be cognitively fit, but hard to be around because you're pushy or hyperactive."

Around the time of Gardner's historic science project, the U.S. military got interested in sleep-deprivation research: Could soldiers be trained to function in sustained warfare with very little sleep? The original studies seemed to say yes. But when the military put soldiers in a lab to make certain they stayed awake, performance suffered. Cumulative deficits accrued with each night of suboptimal sleep. The less sleep the soldiers got, the more deficits they suffered the next day. But as with my own residency experience, they couldn't tell that they had a deficit.

"They would insist that they were fine," said Dinges, "but weren't performing well at all, and the discrepancy was extreme."

This finding has been replicated many times over the intervening decades, even as many professions continue to encourage and applaud sleep deprivation. In one study published in the journal Sleep, researchers kept people just slightly sleep deprived-allowing them only six hours to sleep each night-and watched the subjects' performance on cognitive tests plummet. The crucial finding was that throughout their time in the study, the sixers thought they were functioning perfectly well.

Effective sleep habits, like many things, seem to come back to self-awareness.

I drink coffee instead of sleeping, so I'm fine.

Caffeine is the most consumed stimulant in the world. The chemical induces reactions throughout the body that normally occur in intense situations. When we sense danger, for example, the pituitary gland activates the adrenal glands to secrete epinephrine, or adrenaline, into our blood. Adrenaline is the hormone that's meant to be released when we are under stress and need to muster energy to, say, outrun a bear or lift a fallen boulder off our climbing partner. (He's probably not alive anymore, but it's worth checking.) Caffeine increases adrenaline levels in the blood. It has repeatedly been shown to improve athletic performance in the short term, from how high a person can jump to how fast a person can swim.

The hormone surge also creates a buzz. To lift that boulder we need a flood of energy to fuel our muscles, but first we need to think we can lift the boulder. The "psychoactive" component of caffeine is what makes anything seem possible when brainstorming during your third hour in a coffee shop.

Mauricio Alejo

Caffeine works primarily by blocking the action of a chemical called adenosine, which slows down our neural activity, allowing us to relax, rest, and sleep. By interfering with it, caffeine cuts the brake lines of the brain's alertness system. Eventually, if we don't allow our body to relax, the buzz turns to anxiety.

Thanks to caffeine, many of us stimulate that fight-or-flight response not just occasionally, under dire circumstances, but daily, in our offices. Eighty-five percent of U.S. adults consume some form of caffeine most days, with an average daily dose of 300 milligrams (roughly 27 ounces of coffee). Strategic use of small amounts of caffeine can be cognitively advantageous, but at such a high dose, caffeine is likely to throw off our sleep and energy cycles in the long term, altering the body's internal clock. At that point, many people go in search of products to help them sleep.

But there's no real danger in consuming a lot of caffeine, right? Can't caffeine make you live longer?

We frequently hear that drinking a small amount of coffee can be healthy. This always comes back to the evidence that some coffee-drinking is a common behavior among long-lived, healthy people across populations. News stories tend to interpret this evidence optimistically, reporting that coffee may be good for you. In reality, it might just be an interesting correlation. Randomized, controlled trials on nutrition are extremely difficult to conduct, as the effects of dietary changes are complex and often take years, if not a lifetime, to reveal themselves.

Those who claim that coffee is healthful tend to point to its high level of antioxidants. But antioxidant supplements have not been proved to correlate with health or longevity. Antioxidants represent a vast spectrum of substances. Vitamin E is an antioxidant, and taking vitamin-E supplements has been shown to increase men's risk of prostate cancer.

If coffee does have an effect on longevity, it is likely a result of something more global than the potential effect of antioxidants-such as the fact that constant exposure to caffeine, even at low levels, suppresses appetite (in a world where most people eat more than is ideal). Or that it encourages social interaction-it inclines us to go out and do things with people-which itself is generally beneficial to health. These are legitimately positive results. But as with all chemicals, the comprehensive effect of caffeine on our health depends on how, and how much, we use it.

In 2013, a 24-year-old advertising copywriter in Indonesia died after prolonged sleep deprivation, collapsing a few hours after tweeting "30 hours of working and still going strooong." She went into a coma and died the next morning. A family acquaintance wrote on Facebook, "She died because too much of overtime working, and too much kratingdaeng attacks her heart." Kratingdaeng is the Thai name for the product known elsewhere as Red Bull.

Sleep deprivation is clearly linked to heart disease and strokes. Beyond that, the vitamin/caffeine/amino-acid concoctions known collectively as energy drinks have been implicated in thousands of emergency-room visits in recent years; energy-drink-related ER visits doubled from 2007 to 2011, according to the U.S. Substance Abuse and Mental Health Services Administration. For now, this is simply a correlation, with a plausible explanation that one could be causing the other; it is not proof of harm. And yet, notes Michael Jacobson, the head of the Center for Science in the Public Interest, "there are several fatalities possibly related to energy drinks, and several lawsuits. In some people, it appears to be due to underlying heart defects-when they get this dose of caffeine, they succumb."

Although the FDA warns us rather unambiguously that "caffeine overdose is dangerous and can kill you," I've not seen that happen, and Jacobson, a public-health advocate, confirms that except at extraordinarily high levels, caffeine isn't known to kill otherwise healthy people. It may not be the sole culprit in hospitalizations related to energy drinks. After all, many of the people who have been hospitalized after consuming energy drinks are presumably also coffee drinkers, notes Jacobson-but few, if any, have been made acutely ill by coffee.

I can't sleep. Is my phone really keeping me up? Should I seriously not be reading my phone in bed? That seems impossible.

The United Nations declared 2015 to be the International Year of Light and Light-Based Technologies. That summer, the New York Blue Light Symposium brought together experts who are trying to reckon with the invasion of all this new light into our lives. A keynote speaker was the Japanese ophthalmologist Kazuo Tsubota, the president of the International Blue Light Society, which aims to "promote public awareness of pertinent research on the physical effects of light." Its founding followed a 2012 report by the American Medical Association titled "Light Pollution: Adverse Health Effects of Nighttime Lighting."

Of all the things to have health concerns about, nighttime lighting? Well, yes. When light enters your eye, it hits your retina, which relays signals directly to the core of your brain, the hypothalamus. The size of an almond, the hypothalamus has more importance per volume than any other part of your body. Yes, that includes the sex organs-you would have no sex drive without the hypothalamus. This almond is the interface between the electricity of the nervous system and the hormones of the endocrine system. It takes sensory information and directs the body's responses, so that the body can stay alive.

Among other roles in maintaining bodily homeostasis-appetite, thirst, heart rate, etc.-the hypothalamus controls sleep cycles. It doesn't bother consulting with the cerebral cortex, so you are not conscious of this. But when your retinas start taking in less light, your hypothalamus assumes it's time to sleep. So it wakes up its neighbor the pineal gland and says, "Hey, make some melatonin and shoot it into the blood." And the pineal gland says, "Yes, okay," and it makes the hormone melatonin and shoots it into the blood, and you become sleepy. In the morning, the hypothalamus senses light and tells the pineal gland to stop its work, which it does. Test your blood for melatonin during the daytime, and you will find almost none.

All of this is why we're told to minimize screen time before bed. Phones and tablets emit light that's skewed heavily toward the blue end of the visible spectrum, and some research suggests that these frequencies are especially influential in human sleep cycles. Using a "night mode," available on some phones, is supposed to minimize that effect. That's probably worth doing-so long as you don't end up canceling out any benefit by spending more time looking at the lit screen.

Can't I just take a melatonin supplement if I can't get to sleep?

Melatonin is one of the very few hormones that you can purchase in the United States without a prescription. It is considered a dietary supplement and therefore held to essentially no premarket standards of quality, safety, or efficacy. The pharmacist can't give me the eye drops that help control my glaucoma without a prescription. The pharmacist can't give insulin to a diabetic person without the recurring order of a doctor, to which not all people have easy access. But melatonin, which tinkers with the work of the most crucial part of your brain? It's over there in Aisle 5. Buy as much as you like. It's next to the caffeine pills.

In 2015, Ben Yu, who'd dropped out of Harvard to form a biotech start-up, launched a product called Sprayable Sleep, which contains melatonin. Spray it onto your skin, and it's supposed to put you to sleep. (Sprayable Sleep is the company's second product. Its first was the perfect complement: Sprayable Energy, or topical caffeine.)

When I spoke with Yu, he referred to melatonin not as a hormone but as a "biological signaling molecule." I asked him whether he did this because customers might be averse to spraying themselves with a hormone. "I thought that might be a loaded word," he agreed, "but it turns out, people don't seem to care."

In a sleep-deprived culture, the promise of sleep can lead people to abandon caution. In its initial crowd-funding campaign on Indiegogo, Sprayable Sleep raised $409,798. (That's 2,106 percent of what the company set out to raise, collected from nearly 5,000 people.)

Unlike melatonin pills, which are absorbed into and eliminated from the blood before the night is over, Sprayable Sleep is supposed to keep you asleep through the night, as the hormone gradually percolates through your skin and into your bloodstream. I tried it for a couple of weeks, and I did sleep, but it was tough to tell what effect the product was having: I sleep most nights. That said, I can confirm that it didn't burn my skin. Also, that people don't like it when you pretend you are going to spray it on them.

Melatonin supplements have been shown to make some people fall asleep more quickly, but they aren't proven to increase the total time or quality of sleep. And of course, as with most things sold as supplements in the United States, the effects of long-term use are unknown.

What is clear is that supplement overuse can be dangerous. Melatonin is crucial to the functioning of the most finely tuned apparatuses in the body, and David Dinges is especially concerned about its use by young people. As he put it, "No child should have a melatonin supplement-or a caffeinated drink-without a doctor being involved." Adults, he says, "at least might make informed decisions."

The delicate word there is informed. Many people seem engaged in a daily arms race between wakefulness and unconsciousness, using various products to mask and manage poor sleep habits, and ultimately just needing more products. Spray-on caffeine followed by spray-on melatonin. Or alcohol, which only further messes with our physiological rhythms.

So how does one break that cycle? Factors outside of our control-jobs and families and light pollution, to name a few-can make this hard to do. But when possible, here are a few simple ideas that many experts recommend. Try to keep a somewhat constant bedtime and wake-up time, even on weekends. Keep caffeine use moderate, even if you don't feel like a nighttime coffee affects you. The same goes for nightcaps. (Not necessarily a joyless suggestion-maybe you can meet a friend for a beer at 4 p.m. instead of 10 p.m.) Use screens judiciously, too. Remember that even on night mode, a phone is shooting light into your brain. Have sex with someone instead. Or, sometimes preferable, read something on paper.
This article is adapted from James Hamblin's new book, If Our Bodies Could Talk: A Guide to Operating and Maintaining a Human Body.
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