Most groggy teens drag themselves to school by 7:30 most morning. This is a familiar sight to both parents and teachers. Everyone knows that insufficient sleep is common for teens, but few understand that it can also be the source of weight issues.
A recent study found that the less sleep teens got, the more likely they were to be overweight or obese.
Further, the teens who were already obese appeared to suffer more from each hour less they got of sleep. These researchers predicted that increasing teens' sleep time to 10 hours every night could reduce obesity among teens.
The study, led by Jonathan A. Mitchell, PhD, of the Department of Biostatistics and Epidemiology at the University of Pennsylvania, looked at how sleep duration was linked to teens' weights.
The researchers tracked 1,390 teens from ninth grade through twelfth grade, collecting data on their sleeping habits during the weekdays and Saturday for one week every six months.
The researchers also gathered information on the teens' physical activity and took measurements to calculate their body mass index (BMI). The BMI is a ratio of a person's height to weight and is used to determine whether they are a healthy weight.
The teens' BMIs increased overall as the participants aged from 14 to 18, especially among the teens already in the 90th percentile for BMI.
The researchers found that the less sleep the teens got, the higher BMI they had. However, this increase in BMI from shorter sleep was sharper in the teens who were already overweight or obese.
The more obese the teens were, the more their BMI increased relative to the lesser amount of sleep that they got.
The researchers calculated that each additional hour of sleep the teens got translated to a decrease in the teens' BMI. But the decrease was twice as great among teens in the 90th percentile than among teens in the 10th percentile.
Therefore, the more overweight the teens were, the more their weight could benefit from additional sleep.
If all the teens sleeping an average 7.5 hours a night at age 18 increased their sleep to 10 hours a night, the researchers predicted that 4 percent fewer teens would have BMIs over 25, which is the cutoff for being overweight.
The researchers did not control for dietary intake in the study, but they did control for physical activity and found that the BMI difference among the lesser sleep participants was not completely explained by lower activity levels.
They proposed other possibilities for the link. "One mechanism could be that if you have short sleep, you're awake during the dark cycle," Dr. Mitchell told dailyRx. "We should be eating during the day and when it's dark, we shouldn't be eating."
He said animal studies have shown that the animals gain more weight when they eat during the time of day that they should be sleeping than if they only eat during the proper time to be awake. "It's not the total caloric intake, but it's the timing when you eat," Dr. Mitchell said.
William Kohler, MD, the Director of Pediatric Sleep Services at Florida Hospital Tampa and a dailyRx expert, said this study adds to what researchers already know about the link between too little sleep and being overweight.
"This study offers important additional information that corroborates other studies that have been done in younger children and in adults associating insufficient sleep with obesity," Dr. Kohler said. "The article is also important in that it made suggestions in how to improve sleep, including delaying school start time for teenagers to allow them to get more sleep."
The study was published April 8 in the journal Pediatrics. The research was funded by the National Cancer Institute and the National Institutes of Health. The authors declared no conflicts of interest.