Bipolar Disorder - Epidemiology

Epidemiology

The lifetime prevalence of all types of bipolar disorder is thought to be about 4% (meaning that about 4% of people experience some of the characteristic symptoms at some point in their life). Prevalence is similar in men and women and, broadly, across different cultures and ethnic groups.

Lifetime prevalence of bipolar disorder type I, which includes at least a lifetime manic episode, has generally been estimated at 2%. However, a reanalysis of data from the National Epidemiological Catchment Area survey in the United States suggested that 0.8% of the population experience a manic episode at least once (the diagnostic threshold for bipolar I) and a further 0.5% have a hypomanic episode (the diagnostic threshold for bipolar II or cyclothymia). Including sub-threshold diagnostic criteria, such as one or two symptoms over a short time-period, an additional 5.1% of the population, adding up to a total of 6.4%, were classified as having a bipolar spectrum disorder. A more recent analysis of data from a second US National Comorbidity Survey found that 1% met lifetime prevalence criteria for bipolar I, 1.1% for bipolar II, and 2.4% for subthreshold symptoms. There are conceptual and methodological limitations and variations in the findings. Prevalence studies of bipolar disorder are typically carried out by lay interviewers who follow fully structured/fixed interview schemes; responses to single items from such interviews may suffer limited validity. In addition, diagnoses (and therefore estimates of prevalence) vary depending on whether a categorical or spectrum approach is used. This consideration has led to concerns about the potential for both underdiagnosis and overdiagnosis.

Late adolescence and early adulthood are peak years for the onset of bipolar disorder. One study also found that in 10% of bipolar cases, the onset of mania had happened after the patient had turned 50.