April 2 (HealthDay News) -- Persistent bouts of insomnia in young adults can increase their risk of developing depression, says a new report.

A long-term study of almost 600 young adults found that those with annual one-month periods of insomnia found the incidents of sleeplessness gradually increased over two decades, especially among women. In 40 percent of subjects, insomnia developed into more chronic forms over time, according to findings published in the April 1 issue of Sleep.

Insomnia lasting two weeks or longer predicted major depressive episodes and disorders, according to the report. Seventeen percent to 50 percent of subjects with insomnia lasting two weeks or longer later developed a major depressive episode.

"The results show that insomnia seems to be followed by depression more consistently than the other way around. In addition, we found that insomnia tended to be a chronic problem that gets more persistent over time, whereas depression was a more intermittent problem," study author Dr. Daniel J. Buysse, of the University of Pittsburgh, said in a prepared statement.

The study, conducted by Dr. Jules Angst, of Zurich University Psychiatric Hospital in Switzerland, focused on 591 young adults, whose psychiatric, physical and sleep symptoms were assessed with six interviews spanning 20 years.

"We used to think that insomnia was most often just a symptom of depression. However, a growing body of evidence suggests that insomnia is not just a symptom of depression, but that it may actually precede depression. In other words, people who have insomnia but no depression are at increased risk for later developing depression," Buysee said.

Insomnia, the most common of all sleep disorders, is when a person has trouble falling asleep, staying asleep or waking up too early. About 30 percent of adults have symptoms of insomnia.

Insomnia is more common among elderly people. According to a separate Sleep study from University of Rochester researchers in New York, elderly patients being treated for depression were almost two to four times more likely to remain depressed if they had persistent insomnia, compared with patients with no insomnia. Elderly patients receiving standard care for their depression fared worse than those receiving more enhanced care.

SOURCE: American Academy of Sleep Medicine, news release, April 1, 2008