Sleep loses out a lot -- to finals during college, to caring for new babies, to New Year's parties. But when it comes to your weight and diabetes risk, a good night's sleep might be anything but expendable.
A new study shows that after three nights of poor sleep, healthy people can lose their ability to process sugar by 23 percent -- a problem that in the long-term could lead to weight gain and diabetes.
Comparatively speaking, those in the experiment who were deprived of good sleep experienced a drop in metabolism similar to what would have been seen had they gained between 17 and 28 pounds.
The study, published Monday in the Proceedings of the National Academy of Science, suggests a possible explanation for the high number of diabetics who have sleep disorders.
A Chicken-and-Egg' Dilemma
The new take differs from conventional wisdom on the connection; doctors usually think of diabetes causing sleep problems, not the other way around.
"Here's sort of the chicken-and-the-egg syndrome," said Dr. Martin Abrahamson, medical director of the Joslin Diabetes Center in Boston. "This study is the chicken side, not the egg side."
The egg side -- which happens to be the conventional approach -- suggests diabetics are more likely to be obese, and therefore are more likely to develop obesity-induced sleep apnea. In this condition, a person's extra weight bears down on breathing airways, causing people to get short of breath during deep slow-wave sleep. Instead of waking up, the person shifts to a lighter stage of sleep.
Researchers at the University of Chicago wondered whether sleep disorders like sleep apnea could be partially to blame for metabolism problems instead of just being an unwanted side effect.
To find out, researchers monitored sleeping volunteers' brain waves. When they reached slow-wave sleep, the researchers blared sounds loud enough to rouse the volunteers into a lighter sleep stage, but not loud enough to wake them up -- a forced sleep apnea of sorts.
The next day, volunteers got an intravenous dose of sugar and gave blood samples to see how well their bodies absorbed it, which can be measured by insulin sensitivity.
After just three nights of forced sleep problems, eight of the nine subjects' insulin sensitivity readings dropped to levels usually recorded in people at risk for diabetes.
Worse, researchers found that in these subjects, the main insulin secreting organ -- the pancreas -- failed to compensate for the condition by secreting more insulin. This insufficiency is widely believed to be a distinguishing factor between those with temporary insulin resistance and those with chronic metabolic problems.
And this could spell even worse news for those with prediabetes, who are likely already overweight.
"The impact of slow-wave sleep suppression might even be greater in obese subjects," says study author Dr. Esra Tasali.
"It's sort of a Catch-22 situation," says Abrahamson. "If you're already insulin resistant, a sleep problem can make it worse."
If the findings of the new study are confirmed with larger sleep studies, it could reveal a new function of the slow-wave stage of sleep: regulating metabolism.
However, designing such trials may be easier said than done.
"In an ideal world, you'd like to follow people with chronic sleep problems," says Abrahamson. But, he adds, "That's a difficult one to do."
This is because forcibly creating chronic sleep problems in humans is considered inhumane.
But as the number of people with diabetes grows, there will likely be pressure to learn more about the link between sleep problems and diabetes. Abrahamson says he believes sleep disorders in diabetics are "far more common than we previously imagined."
The Age Factor
We may also be working against the clock. How long a person goes into slow-wave sleep naturally dwindles with age, according to Michael Perlis, professor of psychiatry and neurosciences at the University of Rochester in Rochester, N.Y.
As children, he says, our slow-wave sleep may have accounted for up to 20 percent of our nights. But as adults, this portion may be only up to 10 percent -- and as little as 5 percent. The authors of the study believe that lack of slow-wave sleep plays a part in a heightened risk for developing type 2 diabetes as we age.
Perlis says research has already found other health benefits from slow-wave sleep, such as improved brain and immune function. It may also play a part in the release of growth hormone, which helps with bone elongation in children and skin elasticity in adults.
"That's why you see people in California shooting up growth hormone," says Perlis.
But even though good sleep gets harder to come by as we get older, Perlis says, there are natural ways to ensure you get as much slow-wave sleep as you can for your age.
"Though it's counterintuitive, less sleep may be better," says Perlis. "The longer you sleep, the shallower it is."
So frequent catnaps are out, getting good exercise and full night's sleep is in.
"Sleep is 30 percent of our meager lives," says Perlis. "I sure hope it's doing something more than help us get through the night."