Anne Germain is biased toward sleep.

As a sleep researcher at the University of Pittsburgh, she naturally focuses on the somnambulant side of the daily cycle.

But she also believes there is growing evidence that sleep problems are actually the cause of many psychological and physical illnesses, rather than a side effect of them.

"I think it's a valid theory that sleep disorders lead to psychological disorders," said Dr. Germain, who is based at Western Psychiatric Institute & Clinic.

While it's true that depression and stress can affect sleep, she said, "we've paid much less attention to the other possibility, and the more we look into it, the more consistently we find that there is a very strong relationship of sleep problems being associated with all sorts of psychological and physical health problems.

"I have actually contended that sleep disorders are the starting point for depression, anxiety, even substance abuse, because oftentimes when people start drinking heavily, it has to do with trying to get to sleep."

Her views have been influenced by the research she is doing on returning military veterans from Iraq and Afghanistan who have post-traumatic stress disorder and recurrent nightmares.

In the first weeks after a traumatic event -- the death of a friend or a close encounter with a roadside bomb -- veterans' nightmares often replay the event, she said. As time goes on, the content of the dream will change, but its emotional hallmarks will remain the same.

If the cycle of those dreams isn't broken, the nightmares can become chronic and ingrained, spilling over into daytime life in the form of faltering concentration, volatile temper and poor memory.

But when doctors are able to stop the nightmares and make sleep more normal, she said, many of the other symptoms of post-traumatic stress disappear.

"Whether we're dealing with depression, anxiety or post-traumatic stress disorder, when we target sleep problems, we can have a significant improvement in people's daytime functioning," she said.

In the sleep lab at Western Psych, Dr. Germain is now doing brain imaging studies on returning veterans to see how their mental activity differs from that in normal sleepers.

Those results aren't in yet, but in the meantime, she said, there are two effective therapies available to reduce or eliminate nightmares.

One is an older high blood pressure medication called prazosin. It didn't do a very good job of controlling blood pressure, she said, but it turned out to be very effective at combating nightmares because it decreases the output of adrenalin.

The other treatment doesn't involve any medication.

Known as imagery rehearsal therapy, it provides ways for people to rewrite their nightmares into less threatening dreams, and it is effective in more than 90 percent of people who have tried it.

The technique "is as simple as rehearsing new dreams," she said. "We'll tell people to pick a nightmare they can work with, something manageable, and I'll ask them to write it down, and then to flip the page over and write a new dream, and that will be repeated and rehearsed for three times a day, so you train your brain to have a new set of images."

People don't necessarily remember their new dreams after the rescripting, she said, but they will stop having the nightmares.

And sometimes, even if their dreams don't exactly follow the new plot line, they will start out like the old nightmare but then change into something benign.

"So someone who dreams about an intruder will say, 'Yeah, I did dream about this guy knocking on my door and bursting into the apartment, but I'm not sure what happened next and then it morphed into making cookies with my grandmother," she said.

Researchers aren't sure what purpose dreams serve, but they seem to have a strong link to memory.

In fact, one of the primary symptoms of post-traumatic stress is poor memory -- almost as if the nightmares were interfering with the formation of normal memories.

There is also no widely accepted theory for why sleep is so vital, Dr. Germain said, but one leading hypothesis is that we need that downtime so our brains can replenish their glucose reserves, because the brain uses a disproportionate amount of the body's blood sugar.

If people sleep poorly, it doesn't just affect them psychologically. Studies have shown that when we get too little sleep or it is sporadic, our metabolism changes and makes us more likely to gain weight and develop diabetes. Poor sleep also is linked to heart disease and to poor athletic performance, she said.

It also blunts our thinking ability, Dr. Germain said, which is why students "perform much better if they sleep instead of pulling an all-nighter."

Even though there are a few people who can do well on five hours of sleep or thrive on 10 hours a night, the vast majority of people need between 6 1/2 and 8 hours of sleep a night to function well.

In America, getting too little sleep is a much bigger problem than getting too much.

She knows that firsthand, because one of the ironies of being a sleep researcher is that you are often sleep-deprived, at least when you are starting out, because you stay up all night watching other people snooze.

Dr. Germain got into her specialty when she took a summer job as a college undergraduate in a sleep lab in Canada, where she grew up. "I thought it was fascinating to see people dream and to know when they were dreaming but not know what they were dreaming about, and after the first couple of nights in the lab, I was hooked."

She went on to get her Ph.D. at the University of Montreal, and after an internship in New Mexico studying nightmares in sexual assault victims, she came to the University of Pittsburgh in late 2001.

While she specializes in nightmares, she is also interested in solving more common problems, such as insomnia.

One quick piece of advice: If you are waking up in the middle of the night, don't try to read or watch TV in bed. "In other words," she said, "if you're having a problem, go do it somewhere else," because the bed should remain a place of rest.

And while she isn't sure yet why sleep is so crucial, she harbors no doubts that it is.

"When you go to sleep, it's almost like your brain becomes partially a closed-circuit system and it can do whatever needs to be done without any outside interference."