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Night Owls More Likely to Gain Excess Weight

Teenagers and adults who go to bed late on weeknights are more likely to gain weight than their peers who hit the hay earlier, according to a new study from the University of California, Berkeley, that has found a correlation between sleep and body mass index.

Berkeley researchers analyzed longitudinal data from a nationally representative cohort of more than 3,300 youths and adults, and found that for every hour of sleep they lost, they gained 2.1 points on the BMI index. This gain occurred roughly over a five-year period.

Moreover, exercise, screen time, and the number of hours they slept did not mitigate this BMI increase, according to the study published in the October issue of the journal, Sleep.

“These results highlight adolescent bedtimes, not just total sleep time, as a potential target for weight management during the transition to adulthood,” said Lauren Asarnow, lead author of the study and a doctoral student in UC Berkeley’s Golden Bear Sleep and Mood Research Clinic.

BMI is the measure of a person’s weight in kilograms divided by the square of height in meters. A healthy adult BMI range is estimated to be 18.5 to 24.9.

The Berkeley study analyzed data from the National Longitudinal Study of Adolescent Health, which has tracked the influences and behaviors of U.S. teenagers since 1994. Focusing on three time periods – the onset of puberty, the college-age years and young adulthood – researchers compared the bedtimes and BMI of teenagers from 1994 to 2009.

Cartoon drawing of a woman laying awake in bed.

Surveys show that many teenagers do not get the recommended nine hours sleep a night, and report having trouble staying awake at school. The human circadian rhythm, which regulates physiological and metabolic functions, typically shifts to a later sleep cycle at the onset of puberty. Image is for illustrative purposes only.

Adolescents in the study reported their bedtimes and sleep hours while researchers calculated their BMI based on their height and weight.

Surveys show that many teenagers do not get the recommended nine hours sleep a night, and report having trouble staying awake at school. The human circadian rhythm, which regulates physiological and metabolic functions, typically shifts to a later sleep cycle at the onset of puberty.

The results of the study thus suggest that adolescents who go to bed earlier will “set their weight on a healthier course as they emerge into adulthood,” Asarnow said.

About this neurology research

Asarnow is a researcher on UC Berkeley’s Teen Sleep Study, a treatment program designed to reset the biological clocks of adolescents who have trouble going to sleep and waking up. She is also currently an intern in psychiatry at the University of North Carolina.

In addition to Asarnow, co-authors on the study are Allison Harvey at UC Berkeley and Eleanor McGlinchey at Columbia University.

Funding: The study was funded by National Science Foundation, NIH/National Institute of Mental Health.

Source: Yasmin Anwar – UC Berkeley
Image Credit: The image is in the public domain
Original Research: Abstract for “Evidence for a Possible Link between Bedtime and Change in Body Mass Index” by Lauren D. Asarnow, MA; Eleanor McGlinchey, PhD; and Allison G. Harvey, PhD in Sleep. Published online October 1 2015 doi:10.5665/sleep.5038


Abstract

Evidence for a Possible Link between Bedtime and Change in Body Mass Index

Objectives:

The aim of the current study was to examine the longitudinal relationship between bedtimes and body mass index (BMI) from adolescence to adulthood in a nationally representative sample.

Design:

Three waves of data from the National Longitudinal Study of Adolescent Health were used to assess the bedtimes and BMI of 3,342 adolescents between 1994 and 2009. Hypotheses were tested with hierarchical linear models using a two-level, random intercept and slopes model.

Results:

Later average bedtime during the workweek, in hours, from adolescence to adulthood was associated with an increase in BMI over time (b = 0.035 kg/m2 per min later bedtime per 6 years; standard error = 0.016; t = 2.12, degrees of freedom = 3,238, P < 0.05). These results remained significant after controlling for demographic characteristics and baseline BMI. Although sleep duration, screen time, and exercise frequency did not attenuate the relationship between workday bedtime and BMI over time, fast-food consumption was recognized as a significant partial mediator of the relationship between bedtimes and BMI longitudinally.Conclusions:

The results highlight bedtimes as a potential target for weight management during adolescence and during the transition to adulthood.

“Evidence for a Possible Link between Bedtime and Change in Body Mass Index” by Lauren D. Asarnow, MA; Eleanor McGlinchey, PhD; and Allison G. Harvey, PhD in Sleep. Published online October 1 2015 doi:10.5665/sleep.5038

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