A new study published online recently in the American Journal of Health Promotion suggests that keeping to a consistent sleep routine may help people maintain a healthier weight.
Bruce Bailey, a professor in exercise science at Brigham Young University in Provo, UT, and colleagues found that women who woke at the same time and went to sleep at the same every day had lower body fat.
Prof. Bailey suggests going to bed late and sleeping in may do more harm than good:
"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."
While previous studies have looked at sleep patterns and weight, this is the first study to look at the link between consistency of bed and wake time and body fat.
For their study, the researchers examined data on more than 300 young women aged between 17 and 26 attending two major Western US universities.
At the start of the study period, the women were assessed for body composition and were then given activity trackers to record their movements during the day and their sleep patterns at night for 7 consecutive days and nights.
The results showed that:
- A consistent bed time, but particularly a consistent wake time, were linked to lower body fat.
- Sleeping less than 6.5 or more than 8.5 hours a night was tied to higher body fat.
- Sleeping between 8 and 8.5 hours a night was tied to the lowest levels of body fat.
- Quality of sleep also appears to make a difference to body composition.
- Participants whose wake and sleep time varied by more than 90 minutes had more body fat than those whose variations were limited to 60 minutes.
The researchers said they found wake time was particularly tied to body fat. The participants who consistently woke at the same time every day had the least body fat.
Prof. Bailey suggests consistent sleep patterns are probably closely tied to good sleep hygiene.
Altering sleep hygiene likely changes patterns of physical activity, which in turn alters hormones involved with digestion, with a knock-on effect on body fat.
Prof. Bailey's recipe for improving sleep quality is to exercise, keep your bedroom cool, dark and quiet, and only use your bed for sleeping in. He adds that:
"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."
In 2010, researchers reported in the Annals of Internal Medicine that insufficient sleep can make dieters lose muscle instead of fat.
They found participants on a low-calorie diet lost the same amount of weight whether they slept an average of 8.5 hours or 5.5 hours each night. However, while they lost the same amount of weight, the composition was different.