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"These results highlight adolescent bedtimes, not just total sleep time, as a potential target for weight management during the transition to adulthood," says Lauren Asarnow. (Credit: iStockphoto)

BMI

‘Night owl’ teens may gain more weight

Teenagers and adults who go to bed late on weeknights are more likely to gain weight than those who get to sleep earlier.

For a new study, 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. The gain occurred roughly over a five-year period. Further, exercise, screen time, and the number of sleep hours didn’t mitigate the BMI increase.

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.

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

[7 hours of sleep save you from getting sick]

Published in the journal Sleep, the study analyzes data from the National Longitudinal Study of Adolescent Health, which has tracked the influences and behaviors of US 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.

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 findings suggest that adolescents who go to bed earlier will “set their weight on a healthier course as they emerge into adulthood,” Asarnow says.

Other researchers UC Berkeley and from Columbia University are coauthors of the study.

Source: UC Berkeley

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