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Consistent bed time and wake time linked to healthier weight

Study finds women who woke up at same time every day had lower body fat

Prior research has shown not getting enough sleep can impact your weight, but new BYU research finds the consistency of your bed time and wake time can also influence body fat. 

Exercise science professor Bruce Bailey studied more than 300 women from two major Western U.S. universities over the course of several weeks and found that those with the best sleeping habits had healthier weights.

The main findings from the study, published online in the American Journal of Health Promotion:

  • A consistent bed time and, especially, a consistent wake time are related to lower body fat.
  • Getting less than 6.5 or more than 8.5 hours of sleep per night is associated with higher body fat.
  • Quality of sleep is important for body composition.

Women in the study were first assessed for body composition, and then were given an activity tracker to record their movements during the day and their sleep patterns at night. Researchers tracked sleep patterns of the participants (ages 17-26) for one week.

The most surprising finding from the study, according to the researchers, was the link between bed time and wake time consistency and body weight. Study participants who went to bed and woke up at, or around the same time each day had lower body fat. Those with more than 90 minutes of variation in sleep and wake time during the week had higher body fat than those with less than 60 minutes of variation.

Wake time was particularly linked to body fat: Those who woke up at the same time each morning had lower body fat.  Staying up late and even sleeping in may be doing more harm than good, Bailey said.

“We have these internal clocks and throwing them off and not allowing them to get into a pattern does have an impact on our physiology,” Bailey said.

Bailey related consistent sleep patterns to having good sleep hygiene. When sleep hygiene is altered, it can influence physical activity patterns, and affect some of the hormones related to food consumption contributing to excess body fat.

Bailey and his team also found there was a sweet spot for amount of sleep: Those who slept between 8 and 8.5 hours per night had the lowest body fat.

Sleep quality also proved to have a strong relationship to body fat. Sleep quality is a measure of how effective sleep is, or how much time spent in bed is spent sleeping. Those who had better sleep quality had lower body fat. 

To improve sleep quality Bailey recommended exercising, keeping the temperature in the room cool, having a quiet room, having a dark room, and using beds only for sleeping.

“Sleep is often a casualty of trying to do more and be better and it is often sacrificed, especially by college students, who kind of wear it as a badge of honor,” Bailey said.

BYU exercise science professors James LeCheminant and Larry Tucker are coauthors on the paper, as is statistics professor William Christensen.


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Self Discipline
  12/6/2013 1:57 PM by Brent

Travis, I think you are right. People who get more consistent sleep are more self disciplined. That self discipline carries over to other areas of life such as sleep patterns, weight and diet. Further, self discipline carries over into all areas of your life: physical activity, academic achievement, good financial handling.

Lurking variables?
  12/6/2013 11:35 AM by Travis

It appears that there could be lurking variables in this study. It is likely that the healthier individuals also managed their time better including waking up and going to bed at consistent times. It would be interesting to compare the sleep consistency data with physical activity patterns and academic achievement.

  12/4/2013 11:30 PM by Lucas

Jonathan, if you're asking how do they know it was the sleep and not other variables that reduced body fat, it was probably simple correlations. You measure 300 people's sleeping patterns for a while and then their body fats, and you see if there is a pattern. Then you use statistical analysis to see how likely it is that the two variables coincide. (If you've taken statistics then you should know how they calculate this; if not, I won't go into all the details) If the odds of it being a coincidence are too small, say less than 10% chance, then scientists usually assume a correlation. The next step would be to develop theories on exactly what chemical processes in the body are connecting sleep quality and body fat percentages.

What I would like to know is exactly how much less bodyfat consistent sleepers have than non-consistent sleepers. Is it just a percent or two? Or is it something more substantial, like 5 percent or more?

Great Article!
  11/27/2013 10:39 AM by Jonathan

It would be nice to know how the researchers verified that it was sleep patterns and not something else that was affecting both sleep patterns and body weight. Guess I'll have to read the study. Thanks!

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BYU exercise science professor Bruce Bailey.

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Bruce Bailey studied the connection between sleep consistency and body weight.
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