Women who want to maintain a healthy weight and body fat percentage should make sure they’re getting a good quality and adequate amount of zzz’s — or, sleep. Consistently going to bed and waking up around the same time every day may yield dreamy results for women who want to watch their figure. High-quality and consistent sleep is linked to a healthier weight and lower body fat for women, according to a recent study.

Sleep deprivation is a far too common problem in the U.S., with an estimated 50 to 70 million Americans suffering from a sleep or wakefulness disorder, according to the Centers for Disease Control and Prevention. Poor sleep has profound consequences on a person’s long-term health. The Division of Sleep Medicine at Harvard Medical School says that people who consistently fail to get enough sleep are at an increased risk of chronic diseases such as obesity, diabetes, high blood pressure, and heart conditions, which may lead to a shortened life expectancy. Sleep quality and duration have become important factors in establishing a connection between sleep, weight, and body mass index (BMI).

Researchers at Brigham Young University sought to examine the relationship between sleep patterns and body fat in young adult women from two major Western U.S. universities. The sleep and physical activity of 330 women, ages 17 to 26, were monitored for seven consecutive days and nights for the study. The researchers focused on this age group because they believe young adults tend to have more unusual sleep patterns than others. The women were also assessed for body composition along with their height and weight. 

The participants were asked to fill out a sleep log and wear an activity monitor — an accelerometer — for a week, during both the day and night. This device allowed the researchers to determine the quality and duration of the women’s sleep, respectively. The activity monitor also recorded the time when the participants went to bed, even though a sleep log was also filled out.

Participants who got between 6.5 and 8.5 hours of sleep each night tended to have lower body fat percentages. Bruce Bailey, exercise science professor and author of the study, considers 8 to 8.5 hours of sleep a night to be the “sweet spot” for maintaining a healthy weight and a lower body fat in the study. Sleep quality and body fat proved to have a significant relationship. For the study, sleep quality was measured as how effective sleep was, or how much time spent in bed was spent on sleeping. The participants who had better sleep quality were also found to have lower body fat.

Women who got more than 8.5 hours of sleep were found to have really high body fat, but the researchers speculate there could have been external factors that influenced their weight and how much sleep they got at the time of the study, according to news release. Also, those who slept fewer than 6.5 hours had more body fat than those who fell into the best sleep-duration range.

However, the findings emphasize that consistency and quality of sleep are much more important for a person’s health.

"It's not just how much sleep, but the quality of the sleep, and several factors can be used to determine that," said Larry Tucker, an exercise science professor and co-author of the study.

In a similar study, researchers found teenage boys who sleep less have more body fat when compared to girls, whose sleep deprivation had no effect on their body fat percentage. The findings suggest older teenage boys should get adequate sleep to help to maintain a healthier body. The link between BMI and sleep was not found to be as significant as the relationship between sleep and body weight in boys.

Although both studies focused on different genders and age groups, the findings on sleep duration and quality, and weight and body mass index may be applied to men or older age groups.

"There are a number of other studies that show sleep is related to body weight," Bailey said, according to Deseret News. "There's enough evidence that's similar."

Those who wish to improve sleep quality are recommended to exercise, keep the temperature in their room cool, have a quiet and darkroom, and only use beds for sleeping.

The National Sleep Foundation (NSF) says while there is “no magic number” for sleep, the recommended amount of sleep for healthy adults is seven to eight hours of sleep every night. This amount is based on the body’s need to function for optimal performance and sleep lost due to poor sleep habits because of external factors.

Sources: Allen MD, Bailey BW, Christensen WF et al. Objectively Measured Sleep Patterns in Young Adult Women and the Relationship to Adiposity. American Journal of Health Promotion. 2013.

Black KE, Howe AS, Lubransky A, et al. Sleep duration and adiposity in older adolescents from Otago, New Zealand: relationships differ between boys and girls and are independent of food choice. Nutrition Journal. 2013.