Obesity Risk Increases In Those Who Have Late Bedtimes
July 1, 2013

Obesity Risk Increases In Those Who Have Late Bedtimes

Lawrence LeBlond for redOrbit.com - Your Universe Online

Obesity has become one of the top medical issues over the past decade, becoming a worldwide health epidemic with an estimated 35 percent of adults over the age of 20 overweight and 11 percent obese in 2008, according to the World Health Organization.

As obesity rates continuing to rise, the American Medical Association recently labeled obesity as a disease and now a new study is placing some of the blame for increasing waistlines on late bedtimes and chronic sleep restrictions.

In the largest sample of healthy adults studied to date, researchers at the Perelman School of Medicine at the University of Pennsylvania have discovered that adults who routinely hit the hay later at night and are restricted to number of hours slept may be more susceptible to weight gain due to an increased amount of calories often being consumed during night-time hours.

The study, published in the July issue of the journal SLEEP, looked at healthy adults who generally do not go to bed until the early a.m. hours and typically sleep less than five hours. In a controlled laboratory setting, the researchers studied adult subjects who received four hours of sleep per night over five consecutive nights. The subjects in the study were not allowed to go to sleep until 4 am and had to be up by 8 am. Participants of a control group were asked to sleep for 10 hours per night, from 10 pm to 8 am.

The study included 225 healthy, non-obese individuals ranging in age from 22 to 50 years old. The researchers found an overall increase in caloric intake for those who were restricted to four hours of sleep at night, which was due to an increase in the number of meals consumed during the late-night period of wakefulness. Also, the proportion of calories consumed from fat was higher during late-night hours than at any other time during the day.

"Although previous epidemiological studies have suggested an association between short sleep duration and weight gain/obesity, we were surprised to observe significant weight gain during an in-laboratory study," said lead author Andrea Spaeth, a doctoral candidate in the psychology department at the University of Pennsylvania.

The study subjects were served regular meals during the day, at scheduled times. However, food was always available in the lab kitchen for participants who wanted to eat at other times throughout the day, or night. The study subjects were allowed to move around but were not permitted to exercise. The subjects had access to TV, reading, video games and other sedentary activities over the course of the study, which averaged 18 days.

In the sleep-restricted study group, the researchers further found that males gained more weight than females, and African-Americans gained more weight than Caucasians.

"African Americans, who are at greater risk for obesity and more likely to be habitual short sleepers, may be more susceptible to weight gain in response to sleep restriction," said Spaeth. "Future studies should focus on identifying the behavioral and physiological mechanisms underlying this increased vulnerability."

"A number of epidemiological studies have found an association between short sleep duration and weight gain, and ultimately obesity," said senior study author Namni Goel, PhD. "We wanted to examine this in a controlled experimental study to determine whether we would observe weight gain over a short period of time when subjects were sleep-restricted. We also sought to determine the source of such weight gain--that is, whether it was due to an additional intake of calories beyond what was needed to maintain body weight."

"In our study, we found that when adults restrict their sleep by delaying their bedtime and staying up late, they are at increased risk for weight gain because they consume a substantial amount of food and drink late at night which is higher in fat than food and drink consumed during morning, afternoon or evening," said Spaeth. "This late-night eating contributes to weight gain by not only increasing overall daily intake but also by disrupting the timing of caloric intake."