For Young People, Staying Up Late Could Lead to Obesity In Later Life

With every new study on weight gain published in the scientific community, the formula seems to become more complex. The old model that subtracts calories expended from calories consumed and assumes that every 3,000 calories left over will cause one pound of weight gain is mathematically sound, but there are a whole host of other factors that are being explored.

Inherited metabolism has always an issue, of course. In recent years, we’ve learned that exposure to plastics, gut bacteria populations, the type of foods eaten, and even the timing of meals are all parts of the equation as well. Thanks to several studies, you can now add bedtime to the list of factors to consider.

A Direct Connection

A recent study published in the journal Sleep has found a direct correlation between bedtimes and body fat. For this research, Berkeley  pulled data from the National Longitudinal Study of Adolescent Health. For every hour they stayed up later, the students averaged a whopping 2.1 higher BMI by the end of the five-year study.

BMI is a ratio that divides weight by height.  A healthy adult BMI falls between 18.5 and 24.9, so an increase of 2.1 points per hour of later bedtime is a massive impact. Interestingly, the total number of hours slept didn’t have a direct relationship to weight gain. Regardless of how late the students slept or how much sleep they got on weekends, later bedtimes led to higher weight gain. Their BMI was only affected consistently by late bedtimes. 

Night Owls 1.5 Times More Likely To Be Obese

If this is the first you’ve heard of the correlation between late bedtimes and obesity, don’t blame the Australians. They published a study back in 2011 that had similar findings. That study followed 2,200 kids from age 9 to 16, recording their bedtimes, the number of steps they logged on pedometers, and their “screen time” in front of TVs, computers, and video games. Bedtime turned out to be the pivotal piece of data, with kids who stayed up late 1.5 times more likely to become obese than those who went to bed early, even when they got the same amount of sleep.

Researchers were quick to point out that their study was observational, and a correlation between bedtime and obesity doesn’t prove a cause and effect relationship. It’s possible that some other issue, like physical activity or parenting style, is driving both bedtime and obesity. 

Ten Years of Research

As far back as 2006, Dr. Shahrad Taheri from Bristol University was linking late bedtimes to obesity. Writing in the Archives of Disease in Childhood, Dr. Taheri said lack of sleep was “a plausible contributory factor” in the obesity epidemic in American children. He cited research into the effects of sleep loss on hormones that control the desire for calorie-rich foods, hunger, and levels of energy.

Ghrelin, a hunger-signaling hormone, surges 15 percent higher in people who’ve only had five hours of sleep than those who have gotten eight hours. Meanwhile, leptin, a hormone produced by fat tissues when energy stores are low, is 15% lower in those operating only 5 hours of sleep. The effects are long-term, with a lack of sleep at just 30 months of age linking to an increase in obesity at age 7.  

Dr. Taheri pointed out that the link between obesity and lack of sleep seems strongest in children and adolescents. Parents may want to consider removing electronics from kids’ bedrooms and tucking them in a bit earlier. Adults who struggle to maintain their weight may benefit from an earlier bedtime as well.