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Teens, adults who go to sleep late tend to gain weight, study says
Staying up late will likely eventually lead to packed-on pounds, according to Berkeley researchers, who also found that trying to "make up" sleep shortages won't shift the needle on the scale. - photo by Lois M. Collins
Teens and adults who stay up late on weeknights are likely to gain more weight over time than their early-to-bed peers. And trying to catch up on sleep on weekends or by sleeping in won't change the trajectory, according to new research from University of California, Berkeley, and Columbia University that linked sleep and body mass index.

The researchers looked at more than 3,300 youths and adults who had taken part over a 15-year period in The National Longitudinal Study of Adolescent Health Dataset to conclude that lost sleep translated directly into gained weight each hour equaled 2.1 points on the BMI index over the course of about five years.

The body mass index uses an individual's height and weight to determine if the person is overweight or obese. Normal range is 18.5 to 24.9. A BMI of 25 or above is considered overweight, while 30 and above is considered obese.

The findings are published in the journal Sleep. The researchers concluded that "the results highlight bedtimes as a potential target for weight management during adolescence and during the transition to adulthood."

They said that exercise, screen time including cellphones, TVs and computers and number of hours slept did not make up for the impact the late hours have on BMI.

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 Berkeleys Golden Bear Sleep and Mood Research Clinic, in a written statement.

According to background material for the study, many teens fall short of the nine hours' sleep it is recommended they get each night. As a consequence, many of them are tired and/or sleepy 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 release said.

"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.

Nature World Report cited an article from the National Sleep Foundation that said "teens tend to have irregular sleep patterns across the week they typically stay up late and sleep in late on the weekends, which can affect their biological clocks and hurt the quality of their sleep." It noted that many teens "suffer from treatable sleep disorders such as narcolepsy, insomnia, restless leg syndrome or sleep apnea."

Sleep impacts brains and lives at different ages. For instance, in the Reader's Digest book "Outsmarting Alzheimer's," Dr. Kenneth S. Kosik and Alisa Bowman wrote that "the brain's mere three pounds consumes 20 percent of the body's energy. Like any big consumer, the brain spews out toxic waste as it creates thoughts, memories and chemical instructions. One of these waste products is the amyloid protein thought to contribute to Alzheimer's disease."

It takes an adequate amount of sleep to flush that out and those who short themselves may be more prone to developing Alzheimer's, they said.

They noted that with inadequate sleep, the brain shrinks and people are more prone to errors, as well.