"The traditional wisdom has been that mania begins in your 20s and 30s," said Kathleen Ries Merikangas, the study's lead author and chief of the genetic epidemiology branch at the National Institute of Mental Health.

"I think the important thing is for people to recognize that mania does occur in adolescents," she said.

Mania is a mood disorder characterized by excessive energy, a lack of sleep and sometimes risky and impulsive behaviors.

The most common diagnostic definition of bipolar disorder includes alternate cycles of mania and depression, though one type of bipolar diagnosis involves mania alone.

Merikangas said there have been smaller studies estimating how common mania is among children, and she and her colleagues sought to get a better handle on national rates of the disorder in kids.

The study included more than 10,000 teenagers who went through extensive interviews about their moods and behavior.

The research team found that 2.5 percent met the criteria for having had mania and depression, and 2.2 percent of teens had experienced it within the last 12 months.

Also within the year preceding the survey, 1.3 percent of the kids had mania alone and 5.7 percent had depression.

"I think that our data suggest that bipolar disorder is more common in adolescents than previous studies had shown," Merikangas told Reuters Health.

She said it could be because the questions used during the interviews were somewhat broader than what earlier surveys had asked. But all children considered to have a mood disorder in her study met the criteria for diagnosis in the DSM-IV, the standard diagnostic manual for psychiatry.

Merikangas and her colleagues point out in their report, published Monday in the Archives of General Psychiatry, that the rates of mood disorders they found among teenagers are close to what is seen in adults.

According to the National Institute of Mental Health, 2.6 percent of adults have had bipolar disorder in the last 12 months.

"This (study) confirms the impression that onset in adolescents is part of the picture for this disorder for many many patients," said Dr. Robert Findling, director of the division of child and adolescent psychiatry at University Hospitals Case Medical Center, in Cleveland, who was not involved in the new study.

The mood disorders also became more common as kids got older.

For instance, 1.4 percent of 13 and 14 year olds met the criteria for mania whereas nearly twice as many 17 and 18 year olds had the disorder.

Dr. Benjamin Goldstein at the Sunnybrook Research Institute in Toronto said this study has made the greatest effort to date in determining how widespread bipolar disorder is among youth.

"I think what stuck out to me most was how severely impaired the adolescents were who were described as having bipolar disorder," said Goldstein, who did not participate in the research.

About one out of every five teens with mania and depression had made a suicide attempt, and more than half had an anxiety or behavior disorder as well.

The study found that only about half of kids with mania and depression had been treated for the disorder.

Goldstein said there are effective treatments for kids with mood disorders.

The study results don't necessarily suggest that the rates of bipolar symptoms in teens are rising.

More likely, Goldstein said, increasing numbers of teens who seek treatment for a psychiatric problem are being diagnosed with bipolar disorder.

"The take home message is that adolescence is when we really see bipolar disorder begin, so we should shift our focus of prevention and intervention earlier in the lifespan," Merikangas said.

SOURCE: bit.ly/LGbMKa Archives of General Psychiatry, online May 7, 2012.

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