Ever wish you had the luxury of staying up late and sleeping in? Be careful what you wish for. According to a new study, night owls with insomnia may have a harder time of it than early risers, despite spending more time asleep.

The conclusion comes from 312 insomniacs—those who have trouble falling or staying asleep or who have poor quality sleep—who went to the Stanford Sleep Disorders Clinic in California for group therapy. Patients filled out a series of questionnaires about their sleep habits, mental health and attitudes about sleep.

Researchers categorized each patient as a morning or evening person, or an intermediate case, depending on when they went to bed and the time of day they preferred to do things. Compared with the morning and intermediate types, night owls went to bed an hour or more later but reported more time spent sleeping and more time in bed. On average, they slept 6.4 hours, compared with 5.9 for early risers, and spent 8.7 hours in bed compared with 7.9.

"Even after we adjusted for the severity of their insomnia [the amount of time they spent awake in bed], there were still differences between the night owls and the morning people," says Jason Ong, a behavioral sleep psychologist at Stanford University, and lead author of a report published this week in the Journal of Clinical Sleep Medicine. For one thing, night owls were less consistent in when they went to bed and got up.

In addition, "they seemed to hold more negative and more rigid beliefs about what their sleep should be," Ong says. Night owls reported feeling less in control of their sleep and feeling that they have a hard time getting through the day with less sleep, which might perpetuate insomnia, the researchers say. And they had more risk factors for depression.

Thirty percent of the population reports some symptoms of insomnia, which can affect a person's job performance and may contribute to depression, obesity, heart disease and diabetes.

The result, Ong says, suggests that night owls suffering from insomnia might need different treatment than morning or day people do, perhaps because of problems with their internal clocks, called the circadian system. "It seemed like, anecdotally, it was a little more difficult to work with night owl types," he says. "This provides some evidence that, hey, there are some differences."