Children diagnosed with depression at very young ages are very likely to suffer the disorder well into their adolescent years, if not farther, says new research out of Washington University in St. Louis.

Findings published in the July issue of the The American Journal of Psychiatry showed depressed preschoolers were 2.5 times more likely than undiagnosed peers to be affected by the condition through much, if not all, of their primary and middle-school years.

"It's the same old bad news about depression; it is a chronic and recurrent disorder," child psychiatrist Joan L. Luby, who directs Washington University's Early Emotional Development Program, said in a news release. "But the good news is that if we can identify depression early, perhaps we have a window of opportunity to treat it more effectively and potentially change the trajectory of the illness so that it is less likely to be chronic and recurring."

Researchers explained the study was designed to follow children as they grew and to evaluate them for depression and other psychiatric conditions.

But, if it was discovered children were seriously depressed or in danger of harming themselves, or their caregivers requested treatment, they were referred for more immediate help from mental health providers.

During the study, a research team followed 246 children, enrolled in the study as preschoolers, from the time they were about 3 years old, up until they turned 12.

The children and their primary caregivers attended up to six annual and four semiannual assessments, during which they were screened using a tool called the Preschool Feelings Checklist, which helps doctors evaluate patients through age-appropriate diagnostic interviews.

Throughout the study, caregivers were interviewed about their children's expressions of sadness, irritability, guilt, sleep, appetite and decreased pleasure in activity and play.

Meanwhile, researchers also used two-way mirrors to evaluate child-caregiver interactions, as the team's earlier observations had revealed the recurrence of depression can be linked to a lack of parental nurturing.

While 74 of the child participants were diagnosed with depression at the start of the research, six years later it was determined 79 of those studied met the full criteria for clinical depression, according to the latest standards set by the American Psychiatric Association -- considered the most up-to-date official guidelines for diagnosing and treating psychiatric illnesses.

More than 51 percent of the 74 children originally diagnosed with depression as preschoolers also demonstrated signs of depression as school-age youths.

In contrast, only 24 percent of the 172 children not initially depressed as preschoolers ended up developing depression during their elementary and middle school years.

"Preschool depression predicted school-age depression over and above any of the other well-established risk factors," Luby explained. "Those children appear to be on a trajectory for depression that's independent of other psychosocial variables."

Luby asserted her findings directly contradict doctors and scientists who have long maintained children as young as 3 or 4 cannot be clinically depressed. She therefore argues for the inclusion of depression screenings during regular medical checkups for preschoolers.

"The reason it hasn't yet become a huge call to action is because we don't yet have any proven, effective treatments for depressed preschoolers," she said. "Pediatricians don't usually want to screen for a condition if they can't then refer patients to someone who can help."