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NEW YORK – Curing insomnia in people with depression could double their chance of a full recovery, scientists are reporting. The findings, based on an insomnia treatment that uses talk therapy rather than drugs, are the first to emerge from a series of closely watched studies of sleep and depression to be released in the coming year.

If the new figures hold up, they would represent the most significant advance in the treatment of depression since the introduction of Prozac in 1987. Depression is the most common mental disorder, affecting some 18 million Americans in any given year, according to government figures, and more than half of them also have insomnia.

The new report is based on a preliminary analysis and has yet to be published in a peer-reviewed journal. But experts familiar with it said that the results were plausible and that if supported by other studies, they could lead to major changes in treatment.

“It would be an absolute boon to the field,” said Dr. Nada L. Stotland, professor of psychiatry at Rush Medical College in Chicago, who was not connected with the latest research.

The study is the first of four on sleep and depression nearing completion, all financed by the National Institute of Mental Health. They are meant to evaluate a brand of talk therapy for insomnia that is cheap, usually effective, but not currently a part of standard treatment.

The new report, from a team at Ryerson University in Toronto, found that 87 percent of patients who resolved their insomnia in four biweekly talk-therapy sessions also fully recovered from their depression after eight weeks of treatment, either with an antidepressant drug or a placebo pill – almost twice the rate of those who could not shake their insomnia. Those numbers are in line with a previous pilot study of insomnia treatment at Stanford.

In an interview, the report’s lead author, Colleen E. Carney, said, “The way this story is unfolding, I think we need to start augmenting standard depression treatment with therapy focused on insomnia.”

Carney acknowledged that the study was small – just 66 patients – and said a clearer picture should emerge as the other teams of scientists release their results. Those studies are being done at Stanford, Duke and the University of Pittsburgh. Carney will present her data on Saturday at a convention of the Association for Behavior and Cognitive Therapies, in Nashville.

Doctors have known for years that sleep problems are intertwined with mood disorders. But only recently have they begun to investigate the effects of treating both at the same time.

Antidepressant drugs like Prozac help many people, as does talk therapy, but in rigorous studies the treatments, administered individually, only slightly outperform placebo pills. Used together the treatments produce a cure rate – full recovery – for about 40 percent of patients.

Adding insomnia therapy, however, to an antidepressant would sharply lift the cure rate, Carney’s data suggest, as do the findings from the Stanford pilot study, which included 30 people.

“It makes good common sense clinically,” said Stotland, the psychiatry professor in Chicago. “If you have a depression, you’re often awake all night, it’s extremely lonely, it’s dark, you’re aware every moment that the world around you is sleeping, every concern you have is magnified.”

Doctors have long considered poor sleep to be a symptom of depression that would clear up with treatments, said Rachel Manber, a professor in the department of psychiatry and behavioral sciences at Stanford, whose 2008 pilot trial of insomnia therapy provided the rationale for larger studies. “But we now know that’s not the case,” she said. “The relationship is bidirectional – that insomnia can precede the depression.”

Full-blown insomnia is more serious than the garden-variety sleep problems most people occasionally have. To qualify for a diagnosis, people must have endured at least a month of chronic sleep loss that has caused problems at work, at home or in important relationships. Several studies now suggest that developing insomnia doubles a person’s risk of later becoming depressed – the sleep problem preceding the mood disorder, rather than the other way around.

The therapy that Manber, Carney and the other researchers are using is called cognitive behavior therapy for insomnia, or CBT-I for short. The therapist teaches people to establish a regular wake-up time and stick to it; get out of bed during waking periods; avoid eating, reading, watching TV, or other activities in bed; and eliminate daytime napping.

This kind of therapy is distinct from what is commonly known as sleep hygiene: regular exercise, but not too close to bedtime, and avoiding coffee and too much alcohol in the evening. These healthful habits do not amount to an effective treatment for insomnia.

In her 2008 pilot study testing CBT-I in people with depression, Manber of Stanford used sleep hygiene as part of her control treatment. She found that 60 percent of patients who received seven sessions of the talk therapy and an antidepressant fully recovered from their depression – compared with 33 percent who got the same drug and the sleep-hygiene therapy.

In the four larger trials expected to be published in 2014, researchers had participants keep sleep journals to track the effect of the CBT-I therapy, writing down what time they went to bed every night, what time they tried to fall asleep, how long it took, how many awakenings they had and what time they woke up.

When the diaries show consistent, seldom interrupted, good-quality slumber, the therapist conducts an interview to determine if there are any lingering issues. If there are none, the person has recovered. The therapy results in sharp reductions in nighttime wakefulness for most people who follow through.

Dr. Andrew Krystal, who is running Duke’s CBT-I study, called sleep “this huge, still unexplored frontier of psychiatry.

“The body has complex circadian cycles, and mostly in psychiatry we’ve ignored them,” he said. “Our treatments are driven by convenience — we treat during the day and make little effort to find out what’s happening at night.”