People have acknowledged the value of sleep for centuries. But they’ve focused primarily on sleep’s impact on brain function. “If you talk to some neuroscientists today, the prevailing view is still that sleep is only for the brain,” says Eve Van Cauter, PhD, professor of medicine at the University of Chicago and an expert on the ways sleep affects endocrine function.
Over the last few decades, sleep researchers across the country have been overturning that view. Their studies indicate that curtailing sleep and getting poor-quality sleep are implicated in many diseases that affect the entire body, including type 2 diabetes, hypertension, cardiovascular disease, cancer and impaired immune function.
One of the most startling observations has come from Van Cauter and her University of Chicago colleagues. Over the course of four studies, they showed that people who don’t sleep enough, night after night, unwittingly trigger a hormonal storm that causes their appetites to rise.
Other researchers followed up with studies and found the implications of Van Cauter’s work borne out in real life: People who sleep fewer hours tend to become overweight or even obese. Even a difference of one hour is significant. Columbia University researchers, for instance, found that people between the ages of 32 and 59 who slept only four hours were 73 percent more likely to become obese than those sleeping seven to nine hours. Even a difference of two hours was significant. Those who slept only six hours were 23 percent more likely to become obese than those sleeping seven hours.
Does this mean we can shed pounds by getting additional shuteye? Maybe, but research hasn’t yet proven this supposition — the studies looking at whether overweight people shed pounds when they sleep more are just getting under way. Still, it’s clear that insufficient sleep encourages weight gain and that getting adequate sleep helps prevent it.
Bleary-Eyed and Craving Cookies
Van Cauter set out to study the connection between sleep loss and appetite after anecdotal reports from sleep studies indicated that subjects were overeating during extended stays in the laboratory. The common assumption was that they ate because they were bored, but she decided to test that assumption. In the first-ever study to make the connection between sleep and appetite, published in 2004 in the Annals of Internal Medicine, Van Cauter’s team brought 12 lean and healthy young men into the lab for two four-hour nights of sleep followed by two 10-hour nights. They found that when the subjects slept for only four hours, they showed dramatic changes in two hormones that regulate appetite.
Blood draws revealed an 18 percent decrease in leptin, a satiety hormone produced by the stomach that tells the brain when the body has had enough food. They also showed a 28 percent increase in ghrelin, a hunger-causing hormone produced by our fat cells indicating that our energy reserves are running low and need to be replenished.
Taken together, these two hormones boosted the young men’s hunger — even though the amount they ate and exercised was the same during their nights of ample sleep. The subjects reported a 24 percent increase in appetite after less sleep, with a special eagerness for chips, cakes and cookies, and breads and pasta.
“This study suggests that there could be long-term consequences with prolonged sleep deprivation — especially if you’re trying to control your food intake or stick to a healthy diet,” says Kristen Knutson, PhD, a University of Chicago assistant professor of medicine who’s been involved in many sleep studies. “They were craving junk food, not apples and carrot sticks.”
Body-Clock Confusion
Researchers know that sleep deprivation disrupts one of the most basic mechanisms in our body: our internal clock. And, studies show that messing with our internal clock may have serious implications for our weight. We evolved over millions of years shaped by the earth’s cycles of day and night, and light and darkness, and our body’s clock still ticks according to those basic cycles.
This clock — often called our circadian rhythm — isn’t just a metaphor. It has a precise location in the brain’s hypothalamus, in two pinhead-size clumps of neurons called the suprachiasmatic nuclei (SCN) that sit above our two optic nerves. The SCN monitors the light coming in through our eyes and, based on the amount and timing of light, regulates vital rhythmic functions throughout the body, including temperature, the release of hormones, and metabolism.
“All the different organs that regulate metabolism have circadian rhythms,” says Phyllis Zee, MD, PhD, professor of neurology and director of the Sleep Disorders Center at Northwestern University. “And when they’re out of sync, it can expose one to changes in metabolism or to choosing inappropriate food or to eating too much.”
Some researchers think late nights fueled by bright lights and glowing computer and TV screens may trick our bodies into thinking we’re in a sort of perpetual summer — a high-activity time when our hunter-gatherer predecessors would have been loading up on readily available carbohydrates in preparation for a long, cold winter.
Playing Catch-up
If we build up a sleep “debt” of an hour or two per night, Monday through Friday, we’re generally not going to be able to make it up in one weekend. We carry that debt and the burden of sleepiness forward, often not even realizing how sleep impaired we are.
“Several studies have shown that after cumulative sleep deprivation, individuals are no longer able to recognize the degree of sleepiness under which they operate,” says Van Cauter. “They think they’re OK, but when their performance is tested, they fail miserably.”
What we need, say some experts, is a new characterization of sleep — one that doesn’t regard it as a time when we just turn ourselves off. We need a new appreciation of slumber as a part of the environmental metronome guiding important cyclical functions in our body — functions that affect our weight, our body chemistry, our neurology and our overall well-being.
Most of us assume the routines of a lean lifestyle — like healthy meals and exercise — are limited to our waking hours. But that point of view leaves out the crucial dark side of our 24-hour cycle, when sleep prepares our bodies and minds to function at their best on the following day. It ignores the fact that our bodies require adequate downtime to regulate systems that have a direct impact on whether we accumulate unwanted weight, or succeed in evading it — now and over the long haul.
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