While the neurocognitive sleep discoveries are impressive, there’s equally groundbreaking research on how sleep affects metabolism.
Five years ago, already aware of an association between sleep apnea and diabetes, Dr. Eve Van Cauter at the University of Chicago discovered a “neuroendocrine cascade” that 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 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 some scientists seem to be finding. In light of Van Cauter’s discoveries, sleep scientists have performed a flurry of analyses on 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 in the U.S.; scholars around the world are considering it, as they watch sleep data fall and obesity rates rise in their own countries.
Three foreign studies showed strikingly similar results. One analyzed Japanese elementary students, one Canadian kindergarten boys, and one young boys in Australia. They all showed that kids who get less than eight hours of sleep have about a 300 percent 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.
In Houston public schools, according to a University of Texas at Houston study, adolescents’ odds of obesity went up 80 percent for each hour of lost sleep.
Sleep’s role in obesity is a comparatively new theory, and one difficult to prove in a controlled experiment. But the traditional approach to solving childhood obesity is an abject failure. The federal government spends over a billion dollars a year on nutrition-education programs in our schools. A recent analysis by McMaster University in Hamilton, Ontario, found that of 57 such programs, 53 had no effect whatsoever, and the four remaining programs’ results were meager at best.
For a long time, there’s been one culprit to blame for these 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 that few people thought it needed to be supported scientifically.
Last year, Dr. Elizabeth Vandewater at the University of Texas at Austin got fed up with hearing scholars blame it all on television. “It’s treated as gospel without any evidence,” she says. “It’s just bad science.” Vandewater analyzed the best large data set 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. “Children trade functionally equivalent things. If the television’s off, they don’t go play soccer,” she says. “They do some other sedentary behavior.”
In fact, while obesity has spiked exponentially since the seventies, kids watch only seven minutes more TV a day. Although 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 doesn’t mean it’s healthy to watch television. But it does mean that something other than television is making kids 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,” says Dr. Richard Atkinson, co-editor-in-chief of the International Journal of Obesity.