(RxWiki News) The risk of becoming overweight if you don't get enough sleep has been known for a while among researchers. The question is what might be the cause of possible weight gain for sleep-deprived folks.
A recent study found evidence that at least some weight gain may have been the result of eating extra calories late at night.
In a controlled experiment, adults who got only four hours of sleep each night ate 30 percent more calories than adults who slept 10 hours.
The sleep-deprived adults ate 500 extra calories during the late night hours when they were awake.
"Get 8 hours of sleep each night."
The study, led by Andrea M. Spaeth, MA, a doctoral candidate in the Department of Psychology at the University of Pennsylvania in Philadelphia, looked at the relationship between poor sleep and weight.
The researchers conducted an experiment with 225 participants, aged 22 to 50, who were not obese. They spent up to 18 days in the Sleep and Chronobiology Laboratory at the University hospital.
Of these participants, 198 adults were assigned to have their sleep restricted during the experiment.
Their weight and calorie intake was compared to 27 adults who did not have restricted sleep.
The members of the group with sleep restrictions were allowed only four hours in bed (4 am to 8 am) for five consecutive nights while those in the control group were allowed 10 hours in bed.
All of the adults were served meals at regular meal times, but they could also get food whenever they wanted from a kitchen at the lab. They were not allowed to exercise.
During the study, the adults getting only four hours or less of sleep gained an average 2.2 pounds compared to those without sleep restrictions, who gained an average 0.24 pounds.
The researchers only had information on calorie intake from 31 of the participants with restricted sleep and six of the patients without restricted sleep.
Based on this data, the participants with sleep restrictions consumed more calories during the days they only had four hours to sleep than the participants who had 10 hours to sleep.
Those with 10 hours to sleep typically consumed about 100 percent of the daily caloric requirements for their age and weight. In other words, they ate the amount of calories they are supposed to get each day.
The participants with only four hours to sleep consumed 130 percent of their daily requirements — almost one-third more calories than they need each day.
The higher calorie intake among the participants with sleep restrictions was due to more meals. They ate an average 553 calories between the hours of 10 pm and 4 am, when the control participants were in bed.
The sleep-restricted participants also ate more fat during the late night hours. While about 33 percent of their calories came from fat during these late hours, 28 percent of their calories came from fat eaten between 8 am to 3 pm and 29 percent came from fat eaten between 3 pm to 10 pm.
"Chronically sleep-restricted adults with late bedtimes may be more susceptible to weight gain due to greater daily caloric intake and the consumption of calories during late-night hours," the researchers wrote.
William Kohler, MD, the director of the Florida Sleep Institute in Spring Hill, Florida, and a dailyRx expert, said that past studies on children have found that kids who get less sleep each night were more likely to become obese.
He noted that this study was interesting because it was both the shortened sleep time and the later bedtime that appeared to influence weight gain for the participants.
"If they went to sleep late into the night, they were more likely to gain weight," Dr. Kohler said. "But the authors didn't really explain the mechanism. I'm not really sure what the underlying mechanism is."
He said the study might have provided more information for understanding the reasons for the weight gain if the researchers had done more metabolic measurements of the participants.
For example, the researchers could have measured the participants' ghrelin and leptin levels.
"Previous studies have shown that sleep deprivation increases ghrelin," which is the hormone that stimulates the appetite, Dr. Kohler said. Leptin is the hormone signalling that a person is full.
Even without this information, however, the study findings emphasize the need for adequate sleep and appropriate bedtimes, Dr. Kohler said.
"This articles points out the potential for increased caloric intake and weight gain with short sleep and delayed bedtime," he said.
"You need to go to bed at a reasonably early bedtime, and you need to get an adequate amount of sleep for you to function," Dr. Kohler said. "The amount of sleep that people need varies, but most people need seven to seven and a half hours of sleep."
This study was published June 28 in the journal Sleep. The research was funded by the National Institutes of Health, the Department of the Navy, the Clinical and Translational Research Center and the National Space Biomedical Research Institute at NASA.
One author has served as a consultant on NASA grants, as an NIH study section member and as a lecturer at several colleges and sleep medicine meetings.
Another author has served on the scientific advisory council for Mars, Inc. These two authors are also editors for the journal Sleep. They recused themselves from decisions at the journal on whether to accept this manuscript.