Disrupted Sleep May Raise Risk for Obesity, Diabetes: Study
Researchers found altering amount, timing of rest raised blood sugar levels, slowed metabolism
Wednesday, April 11, 2012
Participants in the small study who were only allowed to sleep about six hours a night and who were subjected to shifting sleep-wake cycles had higher blood sugar levels and lower resting "metabolic rates," which is a term that describes how quickly your body burns calories for energy.
Elevated blood sugar levels can lead to diabetes. If diet and exercise aren't changed, low resting metabolic rates can lead to obesity, which in turn elevates the risk for diabetes.
Previous research has shown that people who work the night shift or who continually get too little sleep have high fat levels in the blood and are more likely to be obese and have type 2 diabetes and metabolic syndrome (a cluster of conditions that are associated with increased risk of heart disease), said Dr. Orfeu Buxton, lead author of the new study and an associate neuroscientist at Brigham & Women's Hospital in Boston.
Buxton's research group had previously shown, in a laboratory setting, that people who sleep only five hours a night for a week have a greater risk of diabetes.
This latest study, published April 11 in Science Translational Medicine, involved 21 healthy adults who were sequestered in a laboratory for almost six weeks, their sleep cycles, diet and activities all controlled by researchers.
After an initial period of sleeping normally (about 10 hours a night), the participants had three weeks of restricted sleep (less than six hours per 24-hour period) along with a disruption of their body clock -- or "circadian rhythm" -- brought about by cycles of 28-hour days.
The schedule was similar to that of rotating shift workers.
The final portion of the study consisted of nine days of normal sleeping to "recover."
During the period of sleep deprivation and circadian rhythm disruption, participants' resting metabolic rate decreased while their post-meal blood sugar levels rose, sometimes even to a level considered pre-diabetic. This was because the pancreas wasn't producing enough insulin, said Buxton, who is also an assistant professor in the division of sleep medicine at Harvard Medical School.
Among these participants, the decrease in metabolic rate was enough to amount to about 10 added pounds over the course of a year, the researchers stated.
After the final nine-day rest-and-restoration period, these metabolic abnormalities returned to normal.
Although sleep restriction and chronic circadian rhythm disruption both impair glucose metabolism and increase diabetes risk, they do so in different ways, Buxton explained.
Sleep restriction alone doesn't result in any changes in resting metabolic rate or in blood sugar levels, although it does lead to increased insulin resistance, meaning glucose is not efficiently ushered out of the bloodstream.
But, being aware of the risks inherent in shift work (and world travel) means that people can adjust to compensate.
"You might want to go to the trouble of adapting circadian rhythms on the schedule that's imposed on you, not just the timing of sleep and light and dark periods, but also the teaming of meals so you're not eating when your gut is shut down and not ready to process that food," Buxton said.
Commenting on the study, Dr. Loren Wissner Greene, a clinical associate professor of medicine at NYU Langone Medical Center in New York City, said: "This shows that you can control your own destiny in some way by disordering your own sleep. People could make beneficial or harmful modifications that might affect their own metabolism."
Greene cautioned, however, that the study was a small one and that the connection between metabolic changes and diabetes in this context is far from certain. Also, none of the participants exercised during the study, something which could have altered the findings.
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