It sounds like a dream: getting to bed early for a good night's sleep. But our "to-do" list seems to inevitably get in the way; a work deadline you can't ignore, emails to catch up on, a child needing your attention—all can sidetrack you from getting solid hours of slumber.
Indeed, hyper-busy, working Americans are finding it difficult to carve out time for the recommended 7 to 9 hours of sleep. Recently, the Centers for Disease Control and Prevention detailed results of a 2010 survey, which found that 30 percent of working Americans reported sleeping an average of 6 or fewer hours per day, with night-shift workers logging fewer winks than day-shift workers.
So what's the harm in skimping on an hour or two of sleep each night? Appetite-controlling hormones get thrown out of whack and cravings for unhealthy foods intensify, says Jerry Kram, medical director of the California Center for Sleep Disorders in Alameda, Calif., contributing to weight gain and perhaps even predisposing the body to diabetes. "There isn't a substitute for an adequate amount of sleep," he says.
Hormone roller coaster. Upon review of large observational studies, findings show that the risk for obesity is consistently higher for those who clock less than 6 nightly hours of sleep, says Kristen Knutson, an assistant professor of medicine at the University of Chicago. Knutson, author of a new review paper published in the American Journal of Human Biology, found evidence linking insufficient sleep to an increase in body fat, or BMI (a weight-height ratio). Knuston says studies that took healthy, normal-weight people in their 20s and 30s and restricted their sleep to 4 hours for several nights found that hormone levels involved in appetite regulation changed; leptin, which tells us when we feel full, declined, and ghrelin, which increases appetite, surged. Hunger didn't always translate to healthy cravings, either. Study subjects reported stronger hankerings for starchy carbohydrates such as pasta, cookies, candy, and sweets, than for dairy, fruit, meat, or vegetables.
[See: How to Conquer Food Cravings]
Drop in metabolism. Lack of zzz's will no doubt leave you worn-out and less likely to go to the gym to burn extra calories. Worse, it can wreak havoc on your metabolism, says Orfeu Buxton, an assistant professor at Harvard Medical School and an associate neuroscientist at Brigham and Women's Hospital in Boston. In a small study lead by Buxton, researchers controlled the sleep, diet, and activities of 21 participants for about five weeks to mimic the sleep patterns of shift workers and travelers who experience jet lag."We saw an 8 percent reduction in resting metabolic rate, or the amount of calories you burn to maintain body weight while you rest," he says. "This equates to a potential of 10 pounds of weight gain in a year, with diet and exercise remaining the same." Buxton's study, published in the April issue of Science Translational Medicine, also confirmed previous findings suggesting that when sleep-starved, people tend to eat more and crave unhealthy processed foods.
Not only are we likely to gain weight as a result of interrupted or too few hours of sleep, but we're more likely to put on pounds in the dreaded abdominal region. Lori Roust, an endocrinologist at the Mayo Clinic in Scottsdale, Ariz., notes that our levels of cortisol, dubbed "the hormone of well-being" typically peak between 7 a.m. and 8 a.m. and then trail off during the day, dipping very low at night. "When people don't sleep at night or have a medical problem that doesn't allow them to sleep well (such as sleep apnea), you get higher levels of cortisol at night, which promotes weight and fat gain, mostly in the inter-abdominal region, which is a link to a predisposition of diabetes and heart disease," says Roust.
Risk for diabetes. Buxton's team also found a connection between lack of sleep, interrupted sleep, and a slide toward pre-diabetes. Sleep affects the way our bodies process food. In a matter of three weeks, the pancreas seemed to stop responding to meals normally, making a third less insulin, a hormone that converts sugar to energy, leaving too much blood sugar in the body's system—the hallmark of diabetes. Buxton notes that this main finding held true despite the age or gender of the person.