The analysis, published in the October edition of the journal Sleep, was carried out by researchers at the University of California, Berkeley. Sleep data collected between 1996 and 2009 as part of the National Longitudinal Study of Adolescent Health was carefully aggregated.
Experts tracked the BMI (body mass index) and bedtime of 3,342 teenagers, in order to see if a link could be determined between the two numbers. Three time periods were taken into account: the beginning of puberty, the years of college and early adulthood.
It was established that for every additional 60 minutes spent beyond recommended sleeping hours, teenagers experienced a 2.1 points increase in their BMI, over a period of 5 years.
For people of normal weight, BMIs range between 18.5 and 24.9. An index above 25 suggests the individual is overweight, and at over 30 obesity can be diagnosed.
Therefore, even that an increase of 2 points can mark the difference between healthy and unhealthy. For example, a woman who weighs 140 pounds and is 5′ 5” tall may gain 12 pounds due to sleeping late, causing her to become overweight.
Staying awake late at night predisposes teenagers and young adults to adding extra pounds, even when they lead otherwise healthy lives.
They may sleep the recommended number of hours, they may engage in regular physical exercise, but these efforts are futile if bedtime is significantly delayed.
On the other hand, those who go to bed earlier “set their weight on a healthier course as they emerge into adulthood”, according to Lauren Asarnow, lead study author and UC Berkeley doctoral student in clinical psychology.
“These results highlight adolescent bedtime, not just total sleep time, as a potential target for weight management during the transition to adulthood”, explained the researcher.
According to experts, weight gain could be related to the fact that staying up late makes people more likely to skip breakfast in the morning and to spend their night snacking on fast food.
As prior studies have shown, teenagers nowadays tend to be severely sleep-deprived. Between 45% and 80% of those in this age group get inadequate rest due to extracurricular involvement, part-time jobs, excessive study load and late-night socializing.
In addition, over 60% of those between 18 and 24 tend to sleep after 11 p.m. This disrupts the circadian rhythm, lowers academic performance and negatively impacts mental and emotional health.
In response to these facts, experts recommend that adolescents should get at least 9 hours of rest per night, and commence their sleep at earlier hours, in order to keep themselves healthy and slim.
In theory, bedtime behavior can be easily modifiable, so a change for the better can be achieved without the efforts required by dieting and exercising.
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