Approximately 4.4 percent of U.S. adults may have some form of bipolar disorder during some point in their lifetime, including about 2.4 percent with a "sub-threshold" condition, according to an article in the May issue of Archives of General Psychiatry.
Individuals with bipolar disorder tend to fluctuate between periods of mania, an inappropriately elevated mood, characterized by impulsive behavior and an increased activity level, and periods of depression. They are at increased risk of suicide and other medical problems, such as cardiovascular disease, according to background information in the article. Previously, researchers estimated that about 1 percent of adults had bipolar disorder. But evidence indicates that current diagnostic criteria may be too narrow to effectively detect bipolar disorder in the general population, and that a broader definition of bipolar spectrum disorder would identify many more individuals with bipolar symptoms, the authors note.
Kathleen R. Merikangas, Ph.D., National Institute of Mental Health, Bethesda, Md., and colleagues estimated the national prevalence of bipolar disorder using data from 9,282 individuals chosen to represent the general population. The researchers conducted interviews between February 2001 and April 2003 to assess the presence of bipolar disorder and other psychiatric conditions. Participants were classified as having bipolar disorder I, characterized by at least one episode of mania and one of depression; bipolar disorder II, requiring an episode of depression plus hypomania, a milder form of mania that does not require hospitalization; and a milder, sub-threshold bipolar disorder that involves hypomania with or without depression, otherwise classified as bipolar disorder "not otherwise specified" in the current diagnostic nomenclature of the American Psychiatric Association.