Getting more sleep than average may help with maintaining a healthy body weight, a study of twins suggests.

The genes behind weight gain may work overtime with lack of shut-eye, according to the research in this week's issue of the journal Sleep.

How much sleep we get is driven by both genetics and environmental factors. (Frank Gunn/Canadian Press)

In the study, neurologist Dr. Nathaniel Watson of the University of Washington Medicine Sleep Center in Seattle looked at the height, weight and sleep habits of 604 pairs of identical twins and 484 fraternal twins with an average age of 37.

Sleeping less than seven hours a night was associated with increased body mass index (BMI).

"What we see is that as sleep durations were reduced, the genetic risks of having a high body weight went up," Watson said in a YouTube slideshow.

"So it's suggesting that when you're sleeping less, you're turning on these genetic drivers to how much you weigh."

The heritability of BMI was twice as high among short sleepers than twins who slept longer than nine hours a night, the researchers estimated.

Three factors drive BMI among twins, Watson said:

• Genetics.
• Shared environment such as diet and parenting.
• Non-shared environment that makes twins different from each other.

The study's authors said genetic factors determined 33 per cent of how long twins slept.

Previous research showed genetic influences such as glucose metabolism, energy use and satiety influence BMI. The genetic pathways involved aren't known.

The findings don't mean that sleeping in will drive you to be thinner, but that sleep, in conjunction with diet and physical exercise, becomes more important to body weight than genetics alone.