Everyone has mood swings, but David Roos knows what's it like to be on the very top of the world, and also at the very bottom.

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For reasons unknown to him at the time, the Mount Troy native changed from a high-powered graphic artist to a depressed man with thoughts of suicide who couldn't get off the couch, even as his wife threatened to take their two children and leave.

He was ultimately diagnosed with bipolar disorder, often referred to as manic-depressive illness, and went through years of treatment and therapy that allowed him to function in the world where he had once thrived.

But researchers yesterday at the Sixth International Conference on Bipolar Disorder said thousands of Americans like Roos have bipolar disorder that goes both undiagnosed and untreated.

Without proper treatment, bipolar individuals can experience significant disruptions in almost all areas of their lives, which also can translate to substantial productivity costs in companies across the country, and in some cases, suicide.

A new study estimates that about 4.3 percent of adults in the country suffer from some type of bipolar disorder. This is higher than previous estimates because it also includes sub-threshold bipolar disorder, a milder form of the illness.

"There is quite a large underbelly that we've been missing here," said Ronald Kessler, professor of health care policy at Harvard Medical School and principal investigator of the study. More than 9,200 Americans in 175 different counties and 35 states were interviewed for the study, called the National Co-Morbidity Survey Replication.

Individuals with bipolar disorder often experience periods of mania, including elevated mood, inflated sense of self-esteem, decreased need for sleep, and physical agitation, followed by periods of depression which are characterized by loss of interest in once-enjoyed activities, noticeable change in appetite or body weight, loss of energy, and difficulty concentrating, among other things.

Sub-threshold bipolar disorder can be just as disruptive as the other subtypes of the illness, Kessler said. When asked if their bipolar tendencies had significantly affected any aspect of their lives within the past year, including social and professional activities, 45 percent of people with sub-threshold bipolar disorder said yes, as opposed to 44 percent to 59 percent of people with more severe forms of the disorder.

"Nothing comes close to near these numbers in any other physical or mental disorder," Kessler said.

Kessler and his colleagues estimate that 180 million work days and $25.8 million a year are lost due to absenteeism and presenteeism -- employees who come to work too ill to accomplish anything -- because of bipolar illnesses. In total, 285 million work days are lost because of major depressive disorders.

Suicide is one of the most dangerous aspects of bipolar illness.

"Bipolar disorders are in fact fatal disorders," said Dr. Ross Baldessarini, a professor of psychiatry at Harvard Medical School. The risk of suicide in bipolar patients is more than 20 times that of the general population, and nearly half of all U.S. suicidal deaths each year occur in bipolar patients.

Researchers have tried for years to find a medication that can reduce the risk of suicide in bipolar patients, but yesterday Baldessarini suggested that lithium, a drug that has been used for 55 years, might be the most successful.

In a comprehensive review of studies comparing rates of suicides and attempts in patients undergoing different treatments, Baldessarini and his colleagues found that patients taking lithium had an 80 to 85 percent lower rate of attempts or completed suicides than patients not taking lithium.

Lithium is difficult for some patients and doctors to use, Baldessarini said. Periodic blood tests are needed, and some patients experience weight gain, fluid retention and thyroid disfunction. It also can have subtle psychological effects.

"People who are energetic might feel that their wings are being clipped," he said.

Still, mood stabilizing is an art, and a light touch with lithium can decrease thoughts of suicide and self-harm. Lithium use was common in the United States before new drugs were introduced, and is still commonly used in Europe.

Many researchers at the conference emphasized the need for therapy in addition to medication, rather than just prescribing pills as a quick fix.

David Roos is one of the lucky ones -- he got good treatment and is able to live a normal life, with only mild manic and depressive episodes. Even his bad experiences with medication were worth it for the peace of mind he now enjoys.

Getting diagnosed, he said, is the best thing that ever happened to him.

Doctors "let me know it wasn't something I created -- it was an illness I had," he said. "They saved me life."