Some individuals in Dallas, Houston and elsewhere in Texas need less sleep to function normally than others. So insomnia's effects may depend on just when a person prefers to hit the sack. According to a new Stanford University research study, "night owls" suffer more from insomnia than those who try to get their z's earlier on.

Researchers found that night owls also tended to be more concerned about their insomnia than the early-to-bed folks, despite the fact that they actually spent relatively more time in bed and got more sleep overall.

There may be more severe symptoms among night owl insomniacs, but researchers also found that they exhibited much more distress about their sleep, in terms of attitude. They felt they needed eight hours of sleep, and they're not getting it, and that was associated with feelings of depression and irritability.

According to the researchers, physiological "insomnia" -- which affects 30 percent of American adults -- refers to disorders defined by poor sleep quality and difficulties falling and staying asleep.

Another type of sleep disturbance is known as a "circadian rhythm sleep disorder" (CRSD), which can arise when the hours of your natural internal clock do not line up well with your social or professional schedule. The resulting "mismatch" can undermine your ability to fall asleep or wake up.

Traditionally, CRSD has been viewed as distinct from insomnia. Experts have theorized that, when circadian rhythms match your daily schedule, you should theoretically experience problem-free sleep.

The new study focused on 312 outpatients (60 percent women) who had already started to undergo group behavior therapy for insomnia at the Stanford sleep clinic between 1999 and 2004. The research team asked all the men and women to indicate their usual (pre-insomnia) preference for sleep scheduling -- when they liked going to bed and waking up.

Based on that information, the patients were characterized as either "morning larks" who felt best going to bed early and rising early, or "night owls" who hit the sack late and slept in. There were also "intermediate" types who fell somewhere in between.

After sorting the participants according to their sleep preference, researchers then reviewed week-long sleep diaries which annotated time of lights out, number of awakenings during sleep, time spent out of bed during sleep time, sleep quality, total time spent sleeping, and all sleep-aid drugs consumed. In addition, a series of psychological surveys was administered to detect depression, frustration and negative beliefs related to either insomnia or sleep in general.

The team found that night owl insomniacs spent more time out of bed while trying to sleep, and generally experienced more sleeplessness than either morning larks or intermediate type insomniacs.

Night owls also displayed the most erratic bedtime and wake-time habits, and were relatively more depressed and more frustrated by their insomnia. For example, night owls expressed more concern than the others about the consequences of insomnia and their inability to control sleep. They made up for such deficits by choosing to spend more time sleeping. In this way, they actually racked up more total sleep time than the other study participants.

No group differences, however, were found with respect to the number of times patients awoke during sleep, in their use of sleep-aids, or in the quality of their sleep. And the findings applied equally to men and women.

According the research team, your natural sleeping schedule preference appears connected to the nature of your insomnia. Researchers emphasized, however, that the findings only point to an association between sleep-time preferences and insomnia, rather than any cause-and-effect relationship. They also cautioned that clinical measures of sleep -- such as blood levels of cortisol, melatonin, or changes in body temperature -- were not evaluated. Some of the patients also had medical conditions that could have affected their sleep patterns. Nevertheless, the team believes the findings could someday lead to targeted treatments that hone in on the patient's unique "insomnia profile."

A good night's rest is important to maintaining good health. Night owls might want to consider a change in sleeping habits to make sure they get enough rest.