Despite what past research has shown, getting more sleep may not be all bad for the waistline.
A new study found that getting more than nine hours of sleep a night could turn off some of the genetic activity linked to body weight. That's because, according to researchers, environmental factors such as diet and exercise play a bigger role in determining weight with longer sleep durations.
"In theory, you have control over environmental factors, so the choices you make may have a bigger impact on your weight the longer you sleep," said Dr. Nathaniel Watson, co-director of the UW Medicine Sleep Center in Seattle.
Watson and colleagues analyzed self-reported data on height, weight and sleep from more than 1,000 pairs of Caucasian twins from the University of Washington Twin Registry.
The study also showed that too little sleep is also detrimental, since genetic factors are more influential when people are sleep-deprived. Those genetic pathways, Watson said, are not yet known.
Taken together, their findings suggest that sleeping too much and sleeping too little can adversely affect body weight, and although it's generally accepted that getting too much sleep can contribute to obesity, it may not play as big a role as originally thought.
"The paper is supporting the long-time belief that there is an association between body mass index and duration of sleep, but the effect of more sleep may not be as powerful as we believed," said Dr. David Schulman, medical director of the Emory Sleep Disorders Laboratory. Schulman was not involved in the study.
"There is too much sleep and there is little sleep. There is an amount of sleep where people become less healthy," said Watson. "Most people need between 7 and 9 hours a night."
"We've been telling people about the negative effects of too little sleep, so this paper supports that as well," Schulman said.
Watson said he hopes that research will next focus on determining precisely how genes are involved, which could eventually lead to a drug that targets obesity, something that other sleep specialists find exciting.
"This study shows that a particular population is affected by sleep deprivation and excess sleep and sheds light on that fact that we should investigate whether other populations are also affected in this way," said Dr. Alexandre Abreu, director of the University of Miami Sleep Center. "The fact that having sleep deprivation may trigger a genetic component that can increase body mass index and weight can be a great focus for targeting obesity in our population."