Let’s consider the hidden role sleep has played in the obesity epidemic.
It’s often noted that in the last three decades childhood obesity has tripled. Half of all kids are at least “at risk of being overweight”—a BMI score two clicks down from obesity.
The federal government spends over $1 billion a year on nutrition education programs in our schools. A recent review by McMaster University of 57 such programs showed that 53 had no impact at all—and the results of the four good ones were so meager it was barely worth mentioning.
For a long time, there’s been one culprit to blame for our failed efforts: television. Rather than running around the neighborhood like when we were young, today’s kids sit in front of the boob tube an average of 3.3 hours a day. The connection to obesity seemed so obvious, and was so often repeated, that few people thought it even needed to be supported scientifically.
Dr. Elizabeth Vandewater at the University of Texas at Austin got fed up with hearing fellow scholars blame it all on television with only weak data to support their claim. “It’s treated as gospel without any evidence,” she grumbled. “It’s just bad science.” Vandewater analyzed the best large dataset available—the Panel Study of Income Dynamics, which has extensively surveyed 8,000 families since 1968. She found that obese kids watch no more television than kids who aren’t obese. All the thin kids watch massive amounts of television, too. There was no statistical correlation between obesity and media use, period. “It’s just not the smoking gun we assumed it to be.”
Vandewater examined the children’s time diaries, and she realized why the earlier research had got it wrong. Kids don’t trade television time for physical activity. “Children trade functionally-equivalent things. If the television’s off, they don’t go play soccer,” she said. “They do some other sedentary behavior.”
In fact, while obesity has spiked exponentially since the 1970s, kids watch only seven minutes more of TV a day. While they do average a half-hour of video games and internet surfing on top of television viewing, the leap in obesity began in 1980, well before home video games and the invention of the web browser. This obviously doesn’t mean it’s good for the waistline to watch television. But it does mean that something—other than television—is making kids even heavier.
“We’ve just done diet and exercise studies for a hundred years and they don’t work well, and it’s time to look for different causes,” proclaimed Dr. Richard Atkinson, co-editor-in-chief of the International Journal of Obesity.
Five years ago, already aware of an association between sleep apnea and diabetes, Dr. Eve Van Cauter discovered a “neuroendocrine cascade” which links sleep to obesity. Sleep loss increases the hormone ghrelin, which signals hunger, and decreases its metabolic opposite, leptin, which suppresses appetite. Sleep loss also elevates the stress hormone cortisol. Cortisol is lipogenic, meaning it stimulates your body to make fat. Human growth hormone is also disrupted. Normally secreted as a single big pulse at the beginning of sleep, growth hormone is essential for the breakdown of fat.
It’s drilled into us that we need to be more active to lose weight. So it spins the mind to hear that a key to staying thin is to spend more time doing the most sedentary inactivity humanly possible. Yet this is exactly what scientists are finding. In light of Van Cauter’s discoveries, sleep scientists have performed a flurry of analyses on large datasets of children. All the studies point in the same direction: on average, children who sleep less are fatter than children who sleep more. This isn’t just here, in America—scholars all around the world are considering it, because children everywhere are both getting fatter and getting less sleep.
Three of those studies showed strikingly similar results. One analyzed Japanese first graders, one Canadian kindergarten boys, and Australian young boys the third. They showed that those kids who get less than eight hours sleep have about a 300% higher rate of obesity than those who get a full ten hours of sleep. Within that two-hour window, it was a “dose-response” relationship, according to the Japanese scholars.
Research in the Houston public schools proved this isn’t just fattening up young kids. Among the middle schoolers and high schoolers studied, the odds of obesity went up 80% for each hour of lost sleep.
Van Cauter has gone on to discover that the stage of slow-wave sleep is especially critical to proper insulin sensitivity and glucose tolerance. When she lets subjects sleep, but interrupts them with gentle door knocks just loud enough to keep them from passing into the slow-wave stage (without actually waking the subjects), their hormone levels respond in a way that’s akin to a weight gain of twenty to thirty pounds. As previously noted, children spend over 40% of their asleep time in this slow-wave stage, while older adults are in this stage only about 4% of the night. This could explain why the relationship between poor sleep and obesity is much stronger in children than in adults.
How sleep impacts hormones is an entirely different way of explaining what makes people fat or thin—we normally just think of weight gain as a straightforward calories-consumed/calories-burned equation. But even by that familiar equation, the relation of sleep to weight makes sense. While very few calories are being burned while blacked out on the sheets, at least a kid is not eating when he’s asleep. In addition, kids who don’t sleep well are often too tired to exercise—it’s been shown that the less sleep kids get, the less active they are during the day. So the net calorie burn, after a good night’s rest, is higher.
In a 2005 paper in Archives of Internal Medicine, Dr. Fred Turek called out traditional obesity researchers for ignoring sleep’s effect on metabolism. Turek is Director of Northwestern University’s Center for Circadian Biology and Medicine. He noted that a standard reference guide for physicians on childhood obesity never discusses the effect of sleep loss on weight—not once in 269 pages.
Dr. Atkinson believes the research he’s seen on children’s sleep loss and obesity is positively “alarming.” Yet he regrets that it is just off the radar screens of most obesity researchers.
In 2007, the United States Department of Agriculture and the Centers for Disease Control reported to us that they’d done no independent research on the issue. They weren’t even willing to offer an opinion on the work already done—despite the fact they annually spend hundreds of millions on obesity research and prevention programs. However, within a year, the data had become too powerful to ignore. The CDC now recommends that high schools consider later starts: its representatives are now opining that a change in school start times can change lives.
Despite how convincing all this science is, somehow it still feels like a huge leap of faith to consider giving back an hour of our children’s lives to slumber. Statistical correlations are fine evidence for scientists, but for parents, we want more—we want control.
Dr. Judith Owens runs a sleep clinic in Providence, affiliated with Brown. Recently, a father came in with his fifteen-year-old daughter, who was complaining of severe headaches. Interviewing the patient, Owens quickly learned that her daily routine was a brutal grind; after flute lessons, bassoon lessons, dance classes, and the homework from honors classes, she was able to get only five hours sleep a night before waking every morning at 4:30 to tromp off to the gym. The father wanted to know if a lack of sleep could be causing her headaches. Owens told him that was probably the case. She recommended his daughter cut back on her schedule.
The word “probably” made this father hesitant. He would let her cut back, but only if Owens could prove, in advance, that sacrificing an activity would stop the headaches. Sure, he knew that sleep was important, but was it more important than Honors French? Was it more important than getting into a great college?
Owens tried her standard argument. “Would you let your daughter ride in a car without a seat belt? You have to think of sleep the same way.”
But Owens’ pleadings didn’t persuade. In this dad’s mind, the transaction went the other way around: cutting back was putting his daughter at risk. What if the headaches didn’t stop, and she gave up one of her great passions, like dance, for no reason?
Long before children become overscheduled high schoolers gunning for college, parents—guardians of their children’s slumber—start making trade-offs between their sleep and their other needs. This is especially true in the last hour of our child’s day—a time zone let’s call the Slush Hour. The slush hour is both a rush to sleep and a slush fund of potential time, sort of a petty cash drawer from which we withdraw ten minute increments. During the slush hour, children should be in bed, but there are so many priorities lobbying for another stroke of attention. As a result, sleep is treated much like the national debt—what’s another half-hour on the bill? We’re surviving; kids can too.
Sleep is a biological imperative for every species on earth. But humans alone try to resist its pull. Instead, we see sleep not as a physical need but a statement of character. It’s considered a sign of weakness to admit fatigue—and it’s a sign of strength to refuse to succomb to slumber. Sleep is for Wusses.
But perhaps we are blind to the toll it is taking on us. University of Pennsylvania’s Dr. David Dinges did an experiment shortening adults’ sleep to six hours a night. After two weeks, they reported that they were doing okay. Yet on a battery of tests, they proved to be just as impaired as someone who has stayed awake for 24 hours straight.
Dinges did the experiment to demonstrate how sleep loss is cumulative, and how our judgment can be fooled by sleep deprivation. Nevertheless, it’s tempting to read of his experiment and think, “I would suffer, but not that bad. I would be the exception.” We’ve coped on too-little sleep for years, and managed to get by. We have some familiarity with this.
But when it comes to a child’s developing brain, are we willing to keep taking the same brazen dare?