Sleep lessens the effect genes have on weight

The less sleep you get, the more your genes contribute to how much you weigh. The more sleep you get, the less your genes determine how much you weigh," says lead author Nathaniel Watson, a neurologist and co-director of the University of Washington Medicine Sleep Center in Seattle.

Previous research has shown the connection between sleep and weight, but this study looks at the role of genetics.

Watson and his colleagues analyzed self-reported data on height, weight and sleep duration of 604 pairs of identical twins and 484 sets of fraternal twins in the University of Washington Twin Registry.

Getting enough shut-eye

Sleep needs vary among individuals, but here are some nightly guidelines:

Source: National Sleep Foundation

People were considered to get short sleep if they slept less than seven hours a night; normal sleep if they slept seven to 8.9 hours, long sleep if they slept nine hours or more. The average age of participants was about 37 years; average sleep duration was 7.2 hours a night.

Among findings published online today in the journal Sleep, from the American Academy of Sleep Medicine:

•Those who slept longer at night had lower body mass index (BMI), based on weight and height, than those sleeping less.

•People who sleep less increase their genetic risk of an elevated BMI, Watson says.

•For twins averaging more than nine hours of sleep, genetic factors accounted for about 32% of weight variations; for those sleeping less than seven hours, genetic factors accounted for 70% of weight variations. For those sleeping seven to nine hours, 60% of the variation was due to genetic factors. Other factors that affect BMI include environmental ones.

Both sleep need and BMI are inherited traits, Watson says. "But we see differences in how much twins weigh based on their sleep duration," he adds.

He says researchers don't know which genetic pathways involving weight are influenced by sleep, but they might include those involving hunger, satiety, fat storage, metabolism or other physiological functions.

Scientists have known for years that sleep deprivation increases levels of a hunger hormone and decreases levels of a hormone that makes you feel full. The effects may lead to overeating and weight gain.

The new findings are another good reason to be sure you get enough shut-eye every night, says sleep expert Jodi Mindell, a psychology professor at Saint Joseph's University in Philadelphia. "If you're trying to lose weight, getting enough sleep gives you a fighting chance."