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 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.
The study found that:
· A total of 1.0 percent of participants had bipolar disorder I and 1.1 percent had bipolar disorder II in their lifetimes; in the previous 12 months, 0.6 percent had bipolar disorder I, 0.8 percent bipolar disorder II and 1.4 percent sub-threshold manifestations of bipolar disorder.
· Symptoms began at age 18.2 years for bipolar disorder I, 20.3 years for bipolar disorder II and 22.2 years for sub-threshold bipolar disorder
· 95.8 to 97.7 percent of those with bipolar disorder and 88.4 percent of those with sub-threshold bipolar disorder also had another psychiatric condition, such as an anxiety disorder or substance use disorder, which is a frequent complication of bipolar illness.
· The majority of those with lifetime bipolar disorder (80.1 percent) received treatment, including 69.3 percent of those with sub-threshold bipolar disorder; most of those people sought treatment for the depression rather than for the manic symptoms of bipolar disorder.
· However, over the previous 12 months, only 25 percent of those with bipolar disorder I, 15.4 percent with bipolar disorder II and 8.1 percent with sub-threshold bipolar disorder received appropriate medication
"The present results reinforce the argument of other researchers that clinically significant sub-threshold bipolar disorder is as least as common as threshold bipolar disorder," the authors write. "Although most individuals with bipolar disorder receive treatment owing to co-morbid disorders, the lack of recognition of their underlying bipolarity leads to only a few receiving appropriate treatment." The findings suggest that a substantial proportion of those diagnosed with major depression may actually have a form of bipolar disorder.
More individuals with other psychiatric disorders should also be screened for bipolar disorder, the authors conclude. "Additional research is needed to resolve uncertainty regarding the most appropriate threshold and boundary distinctions for bipolar disorder. This uncertainty remains a major impediment to advancing the understanding of the bipolar disorder spectrum in the population."