Lack of sleep doesn't just make you bleary-eyed and prone to muddled decision-making. It also makes you gain weight and raises your risk for cardiovascular disease and diabetes.
What qualifies as "short sleep" varies by person. But adults generally skimp when they fall below 7 ½ or eight hours, and teenagers need a good solid nine. "We need to get people thinking about sleep the way they think about diet or exercise – that it is part of a total health plan," says Joseph Ojile, a St. Louis, Mo., pulmonary doctor and board member of the National Sleep Foundation. Or, as Orfeu Buxton, a neuroscientist at Brigham and Women's Hospital in Boston and an assistant professor at Harvard Medical School, puts it, "I like to think of sleep, diet and exercise as the three pillars, and they stand together or they collapse together." One sign this view may be spreading: The upscale Equinox health club chain has recently added a sleep expert to the mix of doctors, nutritionists and exercise scientists on its advisory board.
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Researchers have known for a while that sleep deprivation tends to lead to overeating. And several studies, from the University of California–Berkeley, the New York Obesity Research Center and Stony Brook University School of Medicine, have suggested that pulling all-nighters or even just cutting back by a couple of hours makes people particularly vulnerable to the siren calls of fast food, pizza and candy. Short sleep affects hormones that influence hunger and satiety, experts say, and the brain's reward center becomes more active, drawing you to the carbs and fat. Researchers don't know the exact point of sleep deprivation that triggers the cascade of events that may end in pizza or chocolate. "There are tremendous individual differences," says Jonathan Wisor, a sleep scientist at Washington State University.
Buxton's recent research has confirmed that a pattern of insufficient sleep raises your risk for obesity, and diabetes, too. In a study published in Science Translational Medicine in 2012, he and his team allowed well-rested volunteers roughly 5 ½ hours of sleep per day over a three-week period, varying the timing in a manner similar to the experiences of shift workers or people with jet lag. They found that restricting sleep and disrupting the body clock lowered metabolism and spiked blood glucose levels after participants ate breakfast, a sign that the insulin-producing pancreas isn't fully doing its job.
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The sleep-deprived participants saw their basal metabolic rate decline by 8 percent. That may sound insignificant, but if that person had no corresponding change in diet or activity levels, he or she would put on 10 to 12 pounds a year, says Buxton. Earlier this year, a study by researchers at Britain's University of Surrey gave a hint of what the connection might be: Just one week of less than six hours of sleep per night disrupted the activity of some 700 genes, including ones associated with metabolism and the body's immune and stress responses.
Participants in the Buxton-led research were given 30 minutes to finish eating cereal or toast plus juice and fruit. Those who were "circadian disrupted" experienced a 27 percent decrease in the amount of insulin in their bloodstream. Roughly 15 percent of participants reached glucose levels two hours after the meal that are considered prediabetic.
Experts suspect that the results could apply to anyone who works long hours or spends a lot of time staring at a smartphone or tablet just before bed, and to people who suffer from insomnia or sleep apnea. Studies have shown that artificial light from screens may suppress melatonin, which plays a role in the sleep cycle. And a study from the University of Chicago reported at the American Academy of Sleep Medicine meeting in June showed that higher quality sleep, thanks to treatment for sleep apnea, improved glucose levels and insulin sensitivity possibly as much as some oral diabetes medications.
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If you assume you're safe because study conditions tend to be fairly extreme, think again. People who regularly get less than the optimum amount of sleep have been observed to eat 200 to 500 more calories per day than people who do not. "You prefer different foods, more of them, and at the wrong time of day," Buxton says. "Nobody is eating a salad in the middle of the night."
He recommends that people minimize TV and computer time in the two hours before bed, or at least dim the screen. That cold blue color "is the most circadian-disrupting," he says. He also suggests downloading the free app f.lux, which warms up the hue of the display at night.
If it comes to a tough choice, should you skimp on sleep to squeeze in a workout? No. When you drop below 6 ½ or six hours of sleep, says Ojile, "you need sleep more than you need to exercise."
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