What's the right amount of sleep, where we feel rested, good, and our brains function at their best? A group of researchers is going to re-evaluate that magic number.

The National Sleep Foundation currently recommends seven to nine hours a night for adults, but those guidelines were issued more than a decade ago.

"In the last 10 years, there has been a lot of work on the relationship between sleep and our overall health," explained University of Pennsylvania sleep researcher Michael Grandner. "Really looking into seeing how sleep fits alongside other aspects of health like diet, exercise."

Grandner will be part of the team poring over new studies and findings, and making sure the current sleep guidelines are still accurate.

As researchers learn more about the impact of sleep on mood, cognitive functioning and overall health it could become a new American obsession -- think Zumba or the South Beach diet.

"Sleep has huge potential. It may be easier to change than diet, but it may have somewhere in that realm of importance," Grandner said.

Within that seven to nine hour range, optimal sleep depends on the individual, he said.

So, if you're not sure whether you're getting enough sleep, he suggested some scientific experimentation.

"Maybe you might want to try increasing your sleep time by about 10 or 15 minutes for a week or two, see how that goes," Grandner said. "See how you feel, see if you feel any better, any worse, see how other people feel about you."

You might be less cranky and moody when you get more sleep.

The new sleep guidelines are expected to come out next year.