Women who go to bed and wake up at regular times tend to maintain a healthy weight, a new study suggests.
Research has shown that not sleeping enough can have an effect on weight, but this new study from Brigham Young University finds that consistency in sleeping times can influence body fat.
"The message of this study seems fairly straightforward: Sleeping well consistently is associated with lower body fat in young women," said Dr. David Katz, director of the Yale University Prevention Research Center. Katz was not involved with the study.
The study also suggested that better sleep -- characterised by its efficiency, consistency and duration -- is associated with more routine physical activity, he said.
Good sleepers are 'healthier'
"Some of the advantage in body composition from better sleep appears to be the effect of sleep itself, while some may be a product of more activity, " Katz said. "It may also be that exercise facilitates better sleep, or vice versa."
Katz cautioned, however, that this study did not prove a cause-and-effect relationship between sleep and weight.
The report was published online in the American Journal of Health Promotion.
For the study, a team lead by exercise science expert Bruce Bailey collected data on 330 college women. Over a weeklong period, those who slept and woke at consistent times maintained a healthier weight.
Those who went to bed and woke up at or around the same time each day had lower body fat. Those who slept between eight and eight and a half hours had the lowest body fat, the researchers found.
Those whose sleep patterns varied more than 90 minutes had higher body fat than those whose sleep patterns varied less than 60 minutes, the researchers found.
Too much sleep not good either
Getting too little or too much sleep also had an effect on body fat. Sleeping less than six and a half or more than eight and a half hours a night was associated with higher body fat.
Moreover, quality of sleep was important, with those who had better sleep quality having lower body fat, the researchers found.
Sleep quality is a measure of how much time spent in bed is spent sleeping. Bailey said staying up late or sleeping in may be doing 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 the [physical and chemical functioning of our bodies]," Bailey said in a statement.
Consistent sleep patterns are good sleep hygiene, he said. When sleep is changed, it can change physical-activity patterns and affect some hormones involved with metabolism and contribute to excess body fat, Bailey said.
To improve sleep quality, Bailey recommends exercising, using beds only for sleeping, and keeping the bedroom cool, quiet and dark.
Katz said more research is needed since the findings are specific to young women. "But there is no apparent reason why they would not pertain equally to men," he said.
"For now, it is reasonable to reaffirm that sleep matters to weight control and health," Katz said.
Visit the National Sleep Foundation for tips on how to improve your sleep habits.