Quality and Duration of Sleep Linked to Body Fat in College-aged Women

Good quality sleep and a consistent bedtime and wake-up time can contribute to a healthier body weight, according to a new study published in American Journal of Health Promotion.

The study followed 300 college-aged women over the course of several weeks, finding that those with the best sleeping habits had healthier weights.

"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," said Bruce Bailey, an exercise science professor at Brigham Young University who led the research.

Bailey and his colleges found three main takeaways from their study:

• 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.

The women participating in the study were between 17 and 26 years old. When the study began they were assessed for body fat composition and were given an activity tracker to record their movements throughout the day and their sleep patterns at night.

At the end of the study, the researchers learned that women who went to bed and woke up around the same time each day had lower body fat than the others. Among those with less consistent sleep schedules, women with more than a 90 minute variation in when they went to sleep and when they woke up had higher body fat than women who's sleep variance was 60 minutes or less.

The researchers found that there is a "sweet spot" for sleep and low body fat. Women who consistently slept between 8 and 8.5 hours a night had the lowest body fat.

Bailey and his colleagues also measured a strong relationship between quality of sleep and body fat. Sleep quality was measured as the time spent in bed against the time actually spent sleeping. Study participants with higher quality sleep also had lower body fat.

For improved sleep quality, Bailey suggests keeping the room temperature cool, having a quiet, 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.