A new study says that bipolar disorder, while still rare, may be more common than previously thought.

Face-to-face interviews with more than 9,200 U.S. adults showed that 4.3 percent had symptoms of bipolar disorder or related syndromes, say the researchers, who included Ronald Kessler, PhD, of Harvard Medical School.

Kessler's study also says that some people with major depressive disorder also have bipolar symptoms. Bipolar symptoms impair life more than major depression alone, says the study.

The findings were presented in Pittsburgh during the International Conference on Bipolar Disorders.

Read WebMD's "Medical Reference: What is Bipolar Disorder"

About Bipolar Disorder

Bipolar disorder, formerly called manic depression, is a brain disorder. It causes unusual shifts in a person's mood, energy, and ability to function, says the National Institute of Mental Health (NIMH).

Bipolar disorder is severe. It's not the same as the normal ups and downs of life. Bipolar disorder can have extreme effects, raising suicide risk.

Like other mental illnesses, bipolar disorder is treatable. However, it needs consistent attention. In that regard, it's like diabetes or heart disease -- long-term illnesses that take a lifetime of careful management, says the NIMH.

As with any other serious health condition, don't try to handle any mental illness alone. Seeking help is the first step toward a better life. Resources include doctors, psychiatrists, mental health professionals, social workers, and other trained counselors.

Read WebMD's "Is It ADHD or Bipolar Disorder?"

Parsing the Numbers

Kessler's figure is higher than the NIMH's estimate. The NIMH says that in any given year, about 1 percent of U.S. adults -- roughly 2 million people -- have bipolar disorder.

However, Kessler's number goes a bit beyond the strict definition of bipolar disorder. It also includes "sub-threshold" bipolar disorder, says a news release. People with that condition don't quite meet the bipolar diagnosis but are still severely impaired in their ability to lead a normal life.

Participants did not have to say they had been diagnosed with bipolar disorder. They answered a battery of questions, which the researchers screened for symptoms. Interviews were not done with homeless people or those in institutions.

Read WebMD's "New Brain Scan May Diagnose Bipolar Disorder"

Bipolar Disorder, Depression Sometimes Overlap

Kessler's study says a "substantial proportion" of people with major depression also have bipolar symptoms, including a history of euphoria and irritability. Those people often reported irritability as a prominent feature of their depressive episodes, says the study.

Bipolar disorder has a significantly greater impact on a person's ability to go to work or be productive at work than major depression alone, says the study.

The researchers estimate that on an annual basis, about 50 days are "lost" for someone with bipolar disorder, compared with 32 days for someone with major depression. The national yearly price tag for bipolar disorder totals more than $25 billion, says a news release.

"We conclude that previous research has overestimated the societal costs of major depressive disorder and underestimated the costs of bipolar disorder," say the researchers.

Read WebMD's "Your Guide to Types of Mental Illness"

Funding Sources

Funding for the study came from the John D. and Catherine T. MacArthur Foundation, the U.S. Public Health Service, the Fogarty International Center, and the Pan American Health Organization.

Grants also came from several drug companies, including Eli Lilly, Ortho-McNeil Pharmaceutical, GlaxoSmithKline, Bristol-Myers Squibb, and the Pfizer Foundation.

By Miranda Hitti, reviewed by Brunilda Nazario, MD

SOURCES: International Conference on Bipolar Disorder, Pittsburgh, June 16-18, 2005. National Institute of Mental Health: "Bipolar Disorder." News release, University of Pittsburgh Medical Center.