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Later bedtime in adolescents, young adults tied to increased BMI
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A later than average bedtime on weekdays is associated with an increase in BMI over time in adolescents and young adults regardless of sleep duration, according to research in Sleep.
In an observational study investigating the longitudinal relationship between bedtime and BMI, researchers found that each additional hour of delayed bedtime was associated with an increase in BMI of 2.1 kg/m² during the 15-year study period.
Lauren D. Asarnow
“We found that, in a sample of over 3,000 individuals, going to bed later between the ages of 13 and 32 was associated with weight gain over that same time period above and beyond what’s typical for that developmental period,” Lauren D. Asarnow, MS, of the University of California, Berkeley, told Endocrine Today.
Asarnow and colleagues analyzed data from 3,342 adolescents participating in the National Longitudinal Study of Adolescent Health, a study containing health and behavior data on U.S. adolescents aged 13 to 18 years in the first two waves (1994 to 1996), and again at age 18 to 32 years in the third and fourth waves (2001 to 2002 and 2008 to 2009). Sleep time and sleep duration were self-reported in all waves of the study; sleep diaries were not used. Researchers measured height and weight at each wave; BMI was converted to a z score. Questions assessing fast food consumption, screen time and physical activity were included as potential partial mediators. Researchers used hierarchal linear models using a two-level, random intercept and slopes model to test whether later bedtimes would be associated with an increase in BMI.
A later average workday bedtime was associated with an increase in BMI after controlling for baseline BMI, pubertal status, welfare status and sex. The association persisted after controlling for sleep duration, exercise frequency and screen time (P < .05), but fast food consumption was recognized as a significant partial mediator on bedtime and BMI longitudinally, according to researchers.
“Another interesting point, which was surprising to us, is this was true regardless of how much sleep you were getting,” Asarnow said. “Going to bed at 2 a.m., for example, even if you were getting 8 hours of sleep and waking up at 10 a.m., was associated with weight gain.
“We see this as potentially very good news,” she said. “Bedtime is a highly modifiable behavior. Dr. Allison Harvey and her research team in the Golden Bear Sleep and Mood Research Clinic are currently conducting a study, funded by the National Institute of Child Health and Human Development, to see whether changing sleep habits effect weight gain, eating behavior and other outcomes like emotional health and academic performance. We are anxiously awaiting our results.” – by Regina Schaffer
Disclosure: The researchers report no relevant financial disclosures.
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