A complex web of factors can contribute to weight gain and obesity -- not just diet and exercise, but also stress, metabolism, genetics and sleep.
Research linking weight gain and obesity finds that getting more sleep each night may help limit genetic influences on weight. The study raises the tantalizing possibility that people may be able to use sleep to change a genetic predisposition to weight gain.
"The longer you sleep, the less important genetics become in determining what you weigh," explained Dr. Nathaniel Watson, co-director of the University of Washington Sleep Disorders Center. "Does this mean you can sleep yourself thin?" Watson asked. "Probably not. But you can sleep yourself to a point where environmental factors, like diet and activity, are more important in determining your body weight than genetics."
In the study, published online Tuesday in the journal Sleep, researchers looked at more than 1,000 pairs of identical and fraternal twins in the U.S. Those twins provided researchers with information about their weight, height and sleep patterns.
According to the findings, getting less than seven hours of sleep per night was linked to greater body mass index, a measurement of weight relative to height, and to greater genetic influences on BMI.
On the flip side, getting more than nine hours of sleep seemed to suppress genetic influences on participants' weight.
"Shorter sleep creates a permissive environment for the expression of obesity-related genes," Watson said. "Let's say you have identical twins, with the same BMI-related genes. One twin is a short sleeper and the other is a normal sleeper. The short-sleeping twin is going to be turning on the genes related to BMI -- it's a permissive environment. The longer-sleeping twin is not creating that permissive environment."
Other recent studies have looked at the impact that lack of sleep can have on weight, focusing primarily on how sleep-related behaviors such as late-night snacking can drive up weight. Some have focused on the role of hormones leptin (thought to suppress appetite) and ghrelin (believed to trigger hunger.) Those hormones are largely regulated by sleep patterns.
The new study does not attempt to determine the specific genetic pathways involved. That, Watson said, requires additional research.
"It's likely going to be complicated, because there are many things that affect gene expression," he said.
Watson and his co-authors write that outside research has identified more than 20 genes and obesity-related DNA sequence variations associated with obesity that are involved with things that include satiety, energy use and the body's ability to process glucose.
The new study does not set an exact amount of time people need to sleep in order to minimize genetic factors. For research purposes, "normal" sleep duration was considered to be from 7 to 8.9 hours per night.
Instead, the study pointed out the role sleep plays in suppressing the expression of obesity genes. Losing weight through modifiable behaviors may be more effective when the genetic drivers of body weight are mitigated by sleep, the study suggested.
"It seems that more and more environmental exposures interact with genetic predisposition for obesity," said Dr. David Meyre, a professor of pathology and molecular medicine at McMaster University in Canada, who was not associated with the research.
"A paper like this really opens up a path and encourages people in the field to look more carefully at these gene and environment interactions," Meyre said.