The study found that otherwise-healthy adults who were both sleep deprived and sleeping on schedules that put them at odds with their biological clocks -- common problems for millions of people who work at night -- made 32% less insulin, the hormone that controls blood sugar, than they do when they are well rested.
As a result, their blood sugar rose significantly. In some cases, those increases reached pre-diabetic levels.
The number of calories they burned at rest also dropped about 8%. Over the course of a year, researchers think that could translate into a weight gain of nearly 13 pounds.
"What that means is that the modern condition of excess work, excess pressure, no sleep -- all this disruption -- we can't adapt well to it metabolically. This is a maladaptive response to modern life," says researcher Orfeu M. Buxton, PhD, an associate neuroscientist in the division of sleep medicine at Brigham and Women's Hospital in Boston.
Measuring the Impact of Poor Sleep
For the study, published in the journal Science Translational Medicine, researchers had 21 men and women live in carefully controlled conditions in a sleep lab for more than a month.
About half the adults in the study were in their 20s, the other half were in their 60s. All were healthy and well rested at the start of the study.
They lived in dimly lit rooms without windows, which prevented their bodies from adjusting to shifting days and nights.
For three weeks, researchers kept people in the study awake for 28 hours at a stretch. That meant they were sometimes eating in the middle of their biological nights and sleeping during their biological days. They were allowed to sleep for less than six hours in each 24-hour period, conditions meant to create sleep deprivation.
Researchers used blood tests to measure blood sugar before and after meals, and to measure hormones related to stress, energy regulation, and appetite.
During the periods of sleep deprivation and disruption, people burned fewer calories at rest than they did when they'd had adequate sleep. They also had higher blood sugar. That was true regardless of their age or sex.
Previous studies that have looked at the connection between sleep and metabolism have determined that blood sugar goes up after a night of poor sleep because the body's muscles become less sensitive to the hormone insulin. Insulin resistance leads to myriad problems in the body, including diabetes, polycystic ovary syndrome, heart disease, and cancer.
The new study found that insulin resistance isn't the only problem caused by short sleep, however.
Too little sleep appears to prevent the pancreas from making enough insulin to meet the body's energy demands.
"The pancreas is tired," Buxton says, and isn't "responding adequately."
Why that happens, he says, is still a mystery.
"There's plenty of insulin packaged and ready to go. Somehow it's either not sensing the actual glucose level, or not responding with an adequate or typical response," he tells WebMD.
The good news is that the metabolic disruptions reversed after people in the study were once again allowed to get plenty of sleep on a regular schedule.
The study is some of the strongest evidence to date that short and disrupted sleep is bad for the body's metabolism.
Other studies, which have been shorter or based on more indirect evidence, have shown, for example, that children and adults who sleep less than about six hours a night are more likely to be overweight and have diabetes than people who sleep more than that.
"It's not that it's new information. It's that it provides a lot more information about the combined and potential long-term health effects" of sleep disruption and deprivation, says Charles Bae, MD, a neurologist at Cleveland Clinic in Ohio.
Bae is an expert on sleep disorders, but he was not involved in the research.
Advice for the Tired and Overworked: Don't Sacrifice Sleep
"What I tell my patients is to make sleep a priority," Bae says. "For everybody -- and I'm at fault, too -- sleep is the easiest, quickest thing to either get rid of or cut into because we're all so busy."
"On top of that, if you have to work at different hours, and in this economy you take what you can get, that also means you're less likely to get sleep during the day. Especially if you have demands on your time from family and friends," Bae says.
For shift workers, the best solution isn't always an easy one. "You really have to protect that time during the day when you need to be sleeping," he says.
Those three aspects of health support each other, but Buxton says studies show that they also crumble together when any one becomes a lower priority.
"So you have a ton of job demands and you're not getting a lot of sleep. That gives you less energy for exercise," he says. "Similarly, your diet changes. Not only are you hungrier and having cravings for more food, and eating more," but being tired makes it harder to resist all the junk food you're hungry for.
Studies have shown that sleep-deprived people eat more snacks and sugary drinks and fewer fruits and vegetables.
But Buxton says there are ways shift workers can better cope.
"Ideally, you'd pick a shift schedule that's not erratic or rapidly changing from one day to the next. You know, pulling a night every third or fourth day is really brutal," he says.
With a regular schedule, say a solid month of overnight shifts, "it's easier to adapt."
The body's clock can switch to treat night as day and vice versa, but it's important to stay on that schedule, even with meals.
"Eat during your biological day," Buxton says. "Your gut is not ready for food in the middle of the night."