Not getting enough sleep is linked to obesity.

Not getting enough sleep is linked to obesity. A new study by Francesco P. Cappuccio, MD, of Warwick Medical School in the United Kingdom attempted to quantify the cross-sectional relationship between duration of sleep and obesity in both adults and children.

Taking a cross section of the studies done around the world, they found that there was a consistent increased risk of obesity among short sleepers.

This study is important as it confirms that the association between sleep and obesity is strong, and might be of public health relevance.
But it doesn't answer the question yet of whether it's the obesity that is the cause of the short sleep duration, or whether the short duration of sleep is causing obesity.
More studies are neede to answer that question..

And by the way, the recommended nightly sleep for adults is 7-8 hours.