Late bedtimes lead to weight gain, especially in teens, scientists found in a new study.
"Obesity is obviously growing among adolescents and adults, and there's also an epidemic of lack of sleep and later bedtime preference in teens," the study’s lead author, Lauren Asarnow, a doctoral candidate at the University of California, Berkeley, told CBS News
. "There's been some literature looking at the relationship [between] late bedtimes and weight gain cross-sectionally, but no one's ever looked at what happens long-term."
Asarnow and her team analyzed data on more than 3,300 teens and young adults recorded over 15 years, and found that, over a five-year period, a person's body mass index (BMI) increased 2.1 points for every hour of sleep consistently lost.
"Conceivably, if you're going to bed an hour later, over time you could be shifting BMI categories from normal to overweight," Asarnow said. "So even a two-point increase could be clinically significant."
Somewhat surprising to the researchers was the finding that the link between bedtime and BMI was not significantly impacted by exercise, computer screen time, or total sleep time. That means that sleeping late after going to bed late didn't help the weight of the subjects.
The reason late bedtimes and BMI are linked is still to be determined, but so far scientists think it could be a combination of both metabolic and behavioral patterns.
Going to bed late tends to shift or disturb the body's circadian rhythm, and eating habits are also prone to change.
"If you're staying up late you're more likely to be eating junk food late at night," Asarnow said. "People who stay up late are also less likely to eat breakfast and breakfast skipping is associated with weight gain."
The study was conducted in the Sleep and Mood Research Clinic at the University of California, Berkeley. The study findings were published in the most recent issue of the journal Sleep.
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