Worldwide, the prevalence of bipolar disorder type I is estimated to be 0.6%, that of type II is 0.4%, and that of subthreshold bipolar disorder is 1.4%, yielding a total bipolar disorder spectrum prevalence of 2.4%, according to a new report in the March issue of the Archives of General Psychiatry.
These estimates were derived from what the investigators described as the first international data ever collected using Diagnostic and Statistical Manual–IV definitions for the full spectrum of bipolar disorders and standardized measures to survey nationally representative samples in 11 low-income, middle-income, and high-income countries.
Even though prevalence varied from one country to the next, disease severity, impact on daily life, and patterns of comorbidity remained strikingly similar, said Kathleen R. Merikangas, Ph.D., of the Intramural Research Program of the National Institute of Mental Health (NIMH), and her associates in the World Mental Health Survey Initiative.
This World Health Organization (WHO) project "aims to obtain accurate cross-national information on the prevalence, correlates, and service patterns of mental disorders." The investigators conducted in-person, population-based surveys of 61,392 adults in Brazil, Colombia, Mexico, the United States, Bulgaria, Romania, China, India, Japan, Lebanon, and New Zealand.
In addition to the overall prevalences, they found that the 1-year prevalence of bipolar disorder type I was 0.4%, that of bipolar disorder type II was 0.3%, and that of subthreshold bipolar disorder was 0.8%, for a total bipolar spectrum disorder annual prevalence of 1.5%.
In general, high-income countries had the highest prevalences of bipolar disease and low-income countries had the lowest. The United States had the highest prevalence of overall (4.4%) and annual (2.8%) disease, while India had the lowest (0.1% for both). Two exceptions to this rule were Japan, a high-income country with very low overall (0.7%) and annual (0.2%) prevalences, and Colombia, a low-income country with a high overall prevalence (2.6%).
The mean ages at onset were 18 years for bipolar disorder type I, 20 years for bipolar disorder type II, and 22 years for subthreshold bipolar disorder.
Patterns of comorbidity were remarkably consistent among the different countries. Three-fourths of patients with bipolar spectrum disorders also met criteria for other psychiatric disorders, and the majority had three or more of them. "Anxiety disorders, particularly panic attacks, were the most common comorbid conditions (63%), followed by behavior disorders (45%) and substance use disorders (37%)," Dr. Merikangas and her colleagues said (Arch. Gen. Psychiatry 2011;68:241-51).
The association between bipolar disorders and substance use disorders across the globe was particularly striking in light of the large differences between countries in rates of substance use and abuse. "This suggests that [bipolar disorder] can be considered a risk factor for the development of substance use disorders ... [and supports] the need for careful probing of a history of bipolarity among those with substance use disorders," they said.
The proportion of patients with suicidal behaviors rose with increasing severity of bipolar disease. Approximately 10% of those with subthreshold bipolar disorder, 20% of those with bipolar disorder type II, and 25% of those with bipolar disorder type I said that they had attempted suicide over the last 12 months.
This "striking" finding of suicidality, together with the early age at onset and the strong association with other mental health disorders, provides "further documentation of the individual and societal disability associated with this disorder," they noted.
A substantially higher proportion of patients in high-income countries, compared with middle- or low-income countries, reported having used mental health services. Lifetime use of such services was 50% in high-income countries, 34% in middle-income countries, and 25% in low-income countries.
"Because [bipolar disorder] has an average age at onset at one of the most critical periods of educational, occupational, and social development, its consequences often lead to lifelong disability," the investigators said, and this lack of mental health treatment, especially in low-income countries, is therefore "alarming."
"These data also provide the first aggregate international evidence, to our knowledge, that supports the validity of the spectrum concept of bipolarity," they added. The proportion of mood episodes rated as clinically severe, as well as the proportion in which patients reported severe impairment of work, home management, social life, and close relationships, were directly associated with increasingly severe forms of bipolar disease.
This study was supported by the NIMH’s Intramural Research Program, the U.S. Public Health Service, numerous organizations in the participating countries, and numerous drug companies. Dr. Merikangas reported her affiliation with the Intramural Research Program, and one of her associates, Ronald Kessler, Ph.D., reported ties to numerous pharmaceutical companies.