In June 2011, after the sixth game of the Stanley Cup Finals between the Vancouver Canucks and the Boston Bruins, in Boston, the series was locked in a tie. The Canucks, based in the Pacific Time Zone, had lost all the games hosted in Boston. The Bruins, located in the Eastern Time Zone, had fallen in every contest hosted in Vancouver. As the team with the better regular-season record, the Canucks held home-ice advantage for the seventh and deciding game. So when the Bruins arrived in Vancouver the day before that matchup, they went searching for an edge.

“I was getting ready to take the stage for a lecture in Minnesota when my phone rings,” says Charles A. Czeisler, Ph.D., M.D., sitting in a small, windowless conference room outside his office at the Brigham and Women’s Hospital at Harvard Medical School in Boston, where he serves as the chief of the Division of Sleep Medicine. “It’s the Bruins’ team physician, who says, ‘I’m here in Vancouver, and I’m wondering if you have any suggestions for what we might do.’”

Czeisler asked a number of questions about the Bruins’ travel schedule. He discovered that the team planned to take their discipline of napping in the afternoon with them to Vancouver the next day. “I told him that that doesn’t work—the team needs to be napping in the morning in Vancouver, because that is afternoon here in Boston.” In other words, to maximize their energy and mood, the players should keep their bodies on Eastern Time. “There is a circadian rhythm to athletic performance,” he says, referring to the study of the human body’s inner clockwork.

Physiologically, the window for peak focus, strength, reaction time, and physical flexibility arrives in late afternoon or early evening, when “the body is sending out its strongest drive for wakefulness,” says Czeisler. According to him, that’s when most Olympic records are broken. Since the opening face-off was scheduled for 5 p.m. Vancouver time—8 p.m. in Boston—Czeisler understood that if the Bruins napped at just the right time, the game would fall into a wakeful sweet spot.

The team canceled its morning practice the next day. “All the sports-talk guys are freaking out—‘They’re not doing the shootaround before the championship game! What are they thinking?’” he says. “I was pleased to see that they won the game, which was pretty cool.”

In fact, the Bruins shut out the Canucks 4–0. Whether or not the three-hour shift in the team’s nap time played a role, it is increasingly common in today’s competitive sports to encounter teams at both the professional and collegiate levels who are working to manipulate sleep to their advantage. Northwestern University head football coach Pat Fitzgerald instituted team-wide naps after arriving, and last season he imposed sleep-monitoring sensors on his players during the season. In professional baseball, East Coast teams playing home games against West Coast-based teams have a measurable advantage. “They win about 5% more games,” says Czeisler. “And on average, they score about a quarter more runs.” In 2013, a colleague of Czeisler’s at Harvard published the findings of a study in the journal Sleep, arguing that East Coast-based teams in the NFL consistently underperform when competing in away games on the West Coast.

“It’s one thing to see regular people traveling and changing time zones and, say, visiting the Louvre, and not noticing a split-second change in reaction time when looking at a painting,” says Czeisler, who notes that the brain’s normal reaction time to a stimulus is a quarter of a second—which can quadruple or more if the person is severely sleep deprived. “But for an elite athlete, sleep deprivation degrades coordination and the ability to learn and consolidate memories. Your emotions are more volatile, too. Not getting enough sleep will degrade athletic performance.”

Czeisler isn’t the only sleep expert moonlighting in athletics, but he is the only one whose prominence in professional sports has earned him the unofficial title, at least in the NBA, as “the Sleep Doctor.”

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“Athletes don’t get coaching on this,” he says. “They get fitness coaching. They get nutritional coaching. They don’t get sleep coaching.” Among other teams, he has consulted with the NBA’s Minnesota Timberwolves and Portland Trail Blazers, Major League Baseball’s Milwaukee Brewers, and nearly every pro sports team in the greater Boston area. When the New England Patriots were preparing to fly to London in 2012 for the NFL’s yearly overseas regular-season game, the team physicians sought Czeisler’s expertise before they left. And 15 minutes into our conversation at Harvard, he left the room to take a call from a Major League Baseball team he preferred not to name, which was working on schedule preparations for the 2014 season.

For Czeisler, however, the importance of optimizing sleep extends beyond sports. It’s a public health issue, he says, calling sleep the “third pillar” of good health, alongside diet and exercise. If you don’t get enough over time, he says, you run the risk of ailments like heart disease, diabetes, even cancer. More is always better, he says, because research has proven that it is impossible to get too much sleep. Czeisler recommends seven or eight hours a night for regular people, and closer to nine for high-performance athletes.

If you think you can power through on anything less—as a lot of people do—he points to a series of breakthrough studies led by a Danish biologist whose findings were published in 2013 in the journal Science. The researchers zeroed in on one of the fundamental purposes of sleep: to cleanse your brain.

“We replace cells everywhere all the time, but we keep our brain cells for a lifetime because the connections are so complicated, and to retain our memories,” says Czeisler. “So if you’re going to repair the brain, you’ve got to bring the system offline.” The Danish team offered evidence that your spinal fluid flushes out the toxic buildups on your cells during sleep. “During the process, the space between the [brain] cells becomes larger,” says Czeisler. “There is a structural change, with things moving in relation to one another. It would be as if all the buildings in Manhattan shrank, and the alleys and streets got bigger for the garbage trucks. It was remarkable.”

The message is obvious—it’s important to get enough sleep; but for him, it has become a mission. “For someone like Czeisler, it’s not necessarily about individual patients, it’s about everybody,” says Matthew Wolf-Meyer, Ph.D., associate professor of anthropology at the University of California, Santa Cruz, and author of The Slumbering Masses: Sleep, Medicine, and Modern American Life. “He’s using athletes, astronauts—exceptional cases—in order to get people to think about sleep, and to maximize sleep for everybody; he’s working to popularize the science of sleep in ways that clinicians and scientists don’t really do.”

In January, Czeisler traveled to Davos, Switzerland, with Huffington Post founder Arianna Huffington, to attend the World Economic Forum, the annual convention of the world’s top political and business leaders. In 2013, he testified in the wrongful death trial of the late Michael Jackson, arguing on behalf of the pop star’s mother and children that the troubled musician had suffered from “total sleep deprivation over a chronic period” by the time he died.

“Chuck has the most effective communication and lecture skills,” says David Dinges, Ph.D., chief of the division of sleep and chronobiology at the University of Pennsylvania’s psychiatry department. “He is a giant. He’s been an extraordinary influence in his ability not only to make these big discoveries in the field of sleep, but to translate them to the public in a way that people actually understand.”

Czeisler’s pupils now include several multimillionaire professional athletes—guys not always up for sitting through classroom-style lectures about the nature of REM sleep or instructions on when to go to bed. “There’s obviously a learning curve involved, when Chuck is coming from the academic world to the sports world and trying to educate players,” says Ed Lacerte, head trainer for the Boston Celtics. “But it’s easy to work with Chuck—or ‘Doctor Z,’ as I like to call him. He’s been able to sit down with our players one-on-one. The athletes listen to him. We’ve had players go to his lab for sleep studies, and he’s actually gone into their homes to work with them. He’s been accepted fine. His height has certainly helped—I can tell you that.”

Czeisler is 6’4”, with wispy gray hair and an old-fashioned mustache. He is a polite and enthusiastic talker, and a prolific doodler. When you meet him, you discover that he seldom struggles to find the right words to say—but when he does, he squints into the distance as if the rest of his thought lies waiting to be plucked from across the room. As we chat, his smartphone lights up with e-mails and texts. On one occasion he checks his screen. “I guess I did make some friends along the way,” he says, with a squint and a smile. “That was Shaq [former NBA star Shaquille O’Neal] . He’s a really nice guy.”

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Czeisler’s original area of study wasn’t sleep, but biochemistry. The Chicago native, who attended Harvard for his undergrad work and Stanford for grad school, quickly found himself, in the early 1970s, pulled into the burgeoning field of chronobiology and circadian rhythms. These include, among other things, the fluctuations of blood pressure and body temperature, the sleep-wake cycle, and the secretion of hormones, including cortisol—which was the subject of Czeisler’s first research project. “I became fascinated by the effect of sleep on the release of these hormones,” he says. “That’s how I came into the sleep field.”

In the late ’70s, he began a study of sleep patterns in which he allowed several human subjects to sleep whenever they pleased, freeing them of any “time cues.” “There were many studies in the 1930s and ’40s exploring the circadian rhythms of plants and small organisms, and in the 1950s and ’60s scientists were beginning to understand the effects of light on circadian rhythms in other organisms,” he says. But the prevailing wisdom at the time, largely drawn from mid-century German research, was that humans proved to be the exception to the rule—that somehow we, unlike every other organism, are untethered to the basic rhythm of a 24-hour day.

“One of the weird things that happens when people are living free of time cues, however, is that they exhibit periods of circadian rhythms about an hour longer than the 24-hour day,” he says. “They get to bed an hour later every day and wake up an hour later every day.” With the experiment, Czeisler determined that a human’s duration of sleep is dependent on what time of day it is in the body rather than on how long the person has been awake. “Czeisler demonstrated that the period of the human [circadian system] regulates our biological timing just like other animals,” says UPenn’s Dinges. “It was just a tour de force in science.”

When Czeisler and his fellow researchers published his conclusion in the journal Science in 1980, the article ended with a flash of scientific speculation that the findings may have an impact on “shift workers.” “Suddenly I’m in my apartment and I’m getting calls from The London Times about shift schedules,” he says.

The story found an audience among factory owners, and he got a call from Ogden, Utah’s Great Salt Lake Minerals and Chemical Co., a major player in the mining of potash, an ingredient used in fertilizers. He learned that the company’s shift schedules recessed “counterclockwise,” a common industrial practice at the time. Employees worked the night schedule (midnight to 8 a.m.) for a week, then the evening schedule (4 p.m. to midnight) for a week, then the day schedule (8 a.m. to 4 p.m.) for a week. According to Czeisler, this practice was harmful to worker productivity for several reasons.

If you work the 4 p.m.-to-midnight shift, your circadian rhythm dictates that you go to bed sometime around 3 a.m. and wake up sometime around 11 a.m. If you then rotate counterclockwise—to a shift beginning at 8 a.m.—that will require you to force yourself onto an earlier bedtime to wake up at roughly 6 or 6:30 a.m. to get to work. (For obvious reasons, this is not ideal.) But if you rotate in a clockwise direction, from a shift beginning at 4 p.m. to one beginning at midnight, “you are halfway there,” Czeisler says. “The circadian system in humans runs a little more than 24 hours”—demonstrated by his research subjects who unknowingly went to bed an hour later each night—so it’s much easier for your body to roll forward in that direction. For any corporate road warrior who has flown from New York to Los Angeles and adjusted easily to West Coast time—or suffered the consequences of the reverse—this observation will sound familiar.

After the company in Utah implemented his suggestions, production increased and employees reported happier working conditions. Czeisler then founded the Center for Design of Industrial Schedules, a “fatigue risk-management consulting” nonprofit organization that led him to 10 years of “working among smokestacks in Texas” and eventually with professional sports teams. He went on to consult for entities ranging from police departments to Delta Air Lines to the Department of Homeland Security and NASA. He also advised the investment bank Morgan Stanley. “Bankers,” he says, “have the worst sleep schedules of all.”

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Before long, Czeisler received his first desperate phone call from a road-weary celebrity. It was 1989, and the Rolling Stones were gearing up for their Steel Wheels Tour. “Mr. Jagger was having trouble transitioning across time zones,” says Czeisler. “So I created ‘MJ Time,’ his own personal time zone.” Over calls and faxes, Czeisler designed Mick’s schedule and his exposure to light for the tour. He had him black out the windows in hotel rooms, and scheduled his meals to arrive at certain times of the day. “We also shipped special lighting systems so he could be exposed to bright light” when it was “daytime” on MJ Time, but dark in, say, Japan. “I used to get urgent requests before each of his tours, and kept saying, ‘Give me some advanced notice!’ But I did that for like, 10 or 15 years.”

Years later, when Czeisler would get calls from pro sports physicians—the first of whom was a former med school classmate who’d gone on to work for the Portland Trail Blazers—he drew on his work with the Rolling Stones. “Just as we had ‘MJ Time,’ I thought, I’ll take the same approach to the Trail Blazers,” he says. “So I said, ‘Stay on Blazer Time.’”

His work for sports teams doesn’t require him to provide special lighting equipment, but he does pour over the endless airline itineraries, scheduled events, media appearances, and late-night dinners wedged into their increasingly populated schedules across time zones, then engineers the best sleep-friendly schedule he can. And his biggest no-no for everyone, especially athletes, is the red-eye. “It’s impossible to get uninterrupted sleep,” he says.

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Inside the sleep “suites” at the sleep laboratory at Harvard Medical School—the pods where research subjects live during experiments, with electrodes affixed to their bodies—the most glaring feature is the adjustable lighting, which is spread evenly across the paneled ceiling so there are no visible source points or dark areas. Over the years, electric light has become something of a target for Czeisler. When he is on the convention circuit, light is the subject he sermonizes about most.

In the 1990s, he proved that a human being’s biological clock can be reset—your entire bodily rhythm shifted—with exposure to artificial light. He then proved that this applies to blind people as well. “Ordinary room light is only 1% of the intensity of the light outdoors,” he says, “but it has 50% of the resetting ability.” According to him, short-wavelength light is the more insidious influence on your biological clock. These are the beams emitted by your iPad, plasma television, and even eco-conscious lightbulbs. (The old incandescent lightbulbs, according to Czeisler, emit more heat than actual light.) When this short-wavelength light hits the photosensitive retinal ganglion cells in your eye, it halts the release of “sleep-promoting” neurons and “activates arousal-promoting” neurons. It also suppresses the release of melatonin, the brain’s natural chemical for facilitating drowsiness. In our artificially lit world, he says, it’s likely that most of us have shifted our time zones to the point that sleep—the necessary, healthy kind—is increasingly difficult to achieve.

We go to bed late and force ourselves up too early with caffeine, manipulate our time zones, and burden ourselves with enormous sleep debts that would take weeks of vacation to pay back. In terms of public awareness, “we’re in the 1950s with smoking,” Czeisler says. “A few people on the cutting edge are aware”—such as pro sports teams—“but I wouldn’t say society as a whole is adopting it. Nobody has said, when we release the next [light-emitting] tablet, ‘Look at the health and safety consequences!’ No one is viewing light as something that needs to be evaluated. The light sources are getting brighter and worse.”

So he advises you to dim your lights in the evening, and turn off the TV at least an hour or two before bed. If your phone is your alarm clock, buy an alarm clock. “For uninterrupted sleep, keep your phone in a different place,” he says—otherwise you’ll look at it, and it will invariably buzz. If you need to e-mail, he suggests “installing ‘f.lux’ software on your computer, which changes the wavelength of the light on the screen.” I mention that people have had light—lightbulbs, candles—for quite a while, yet have always stayed up past their bedtimes. Isn’t this a little overblown? “When I was growing up, 2–3% of the population slept less than six hours; now it’s 10 times as many,” he says. “We’ve increased by an order of magnitude our per capita light exposure. Take all the people who died on 9/11—twice as many die in motor vehicle crashes every year in the U.S. alone due to sleep deprivation. There are about 60,000 debilitating injuries on the highway [caused by under-slept drivers]. And we’re getting more overweight because we’re sleeping less. As sleep has gone down, waistlines have gone up. When you don’t get enough sleep, your brain goes into starvation mode.”

So, what can we do? “I don’t know the answer,” Czeisler says. “But I don’t think the answer is for the culture to unlearn our modern way of life.” So he recognizes the challenge. “When I was meeting with an NBA team, I started off my talk by mentioning that people are sleeping less today than when I was young. Their star player said, ‘That’s because back then there was less shit to do!’ ”