Later Weekday Bedtimes May Be an Independent Risk Factor for Obesity

In one of my previous posts I detailed how eating close to bedtime impairs your sleep quality, which may confer risk for obesity. Similarly, this week we look at a recent finding that having a consistent later bedtime can lead to increases in BMI over time.

It is important to view obesity from a developmental perspective; in many cases obesity starts in childhood and can progress into adulthood.  In fact, the current childhood obesity rates are alarming.  In 2012 data, 17% of children 2-19 were obese. While this number is down from recent years, this is still far too high.

 When looking at this data, one of the questions is always “why is this happening?’  One potential explanation may simply be how late you decide to go to bed.  A 2015 study by Asarnow and colleagues found that no matter how long participants slept, later weekday bedtimes were associated with increases in BMI over time.  This study not only controlled for sleep duration, but also fast food consumption and exercise frequency.  So, regardless of how long you long you sleep, how infrequently you exercise, or how much fast food you consume, going to bed at a later time can be a risk factor for obesity.

 This is pretty amazing.  This could also help explain why obesity rates in children are so high.  Surveys have shown that around 40% of teens prefer later bedtimes, and onset of puberty delays a night owl’s sleep period even more.  In another study of high school upperclassmen, 60% of them stated that they also prefer staying up late.

 But why is this happening?  Late bedtimes, which can desynchronize your internal and external biological clocks, have been shown to lead to metabolic disturbances such as disturbed glucose and insulin metabolism (my next post will explain how poor sleep is a risk factor for Type 2 Diabetes).  These disturbed process are then what contribute to the physiological changes that lead to increases in BMI.

This has important implications for public health and intervention research.  If future studies are able to replicate this effect, bed times can be a target for prevention and treatment for obesity. This is a very hot topic right now, and it will be exciting to see what comes out in the following years!

Asarnow, L. D., McGlinchey, E., & Harvey, A. G. (2015). Evidence for a Possible Link between Bedtime and Change in Body Mass Index. Sleep.

For statistics on childhood obesity:


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