According to an article on WashingtonPost.com:

"Beyond leaving people bleary-eyed, clutching a Starbucks cup and dozing off at afternoon meetings, failing to get enough sleep or sleeping at odd hours heightens the risk for a variety of major illnesses, including cancer, heart disease, diabetes and obesity, recent studies indicate."

You can read the full article here.

In my own experience, I have seen a tremendous correlation between lack of sleep and increased UC symptoms.