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Course and Prevalence of Bipolar Disorder

Prevalence of Bipolar Disorder

In the general population, about 0.5-2.5% of all people will develop Bipolar I Disorder in their lifetime and anywhere from 2.0-5.0% of the population will develop Bipolar II Disorder [ref].  In total, over 1 in 20 people suffer from a Bipolar Disorder [ref], though some researchers estimate that as many as 1 in 10 people may have a Bipolar Spectrum disorder [ref].

Women tend to be diagnosed with Bipolar II Disorder more often than men, but otherwise there is no clear evidence of any other important gender differences in Bipolar Disorder [ref].

Rates of Bipolar Disorder among adolescents ages 13-18 have been found to be nearly as high as in adults [ref].

Bipolar Disorder ranks among the top ten leading causes of disability in the world, especially among younger people [ref], and Bipolar I and II Disorder are equivalent to each other in terms of the amount of disability and reduced quality of life that they cause [ref].

Course of Bipolar Disorder

Bipolar Disorder can first appear at any point in a person's life, whether in childhood or old age.  The most common time for it to appear is in mid-to-late adolesence [ref]. Other "peaks" when this condition is likely to begin include the mid-twenties and early forties [ref].  Once the disorder appears it usually endures for the rest of the person's life.

Bipolar Disorder is a relapsing-remitting condition, meaning that mood episodes (Major Depressive, Hypomanic, Manic or Mixed) will recur from time to time but the individual will then usually recover and return to better health. On average, people with Bipolar Disorder will endure a mood episode once every two years [ref], though some individuals can experience episodes more frequently than this, especially in the case of Rapid Cycling. People with more severe forms of Bipolar Disorder, such as those who have been hospitalized for this condition, spend an average of 20% of their lifetimes in the midst of mood episodes [ref]. The goal of treatment is to reduce the number of episodes that a person will have and also help them recover more quickly when the episodes occur.

Even when not in a full-blown mood episode, people with Bipolar Disorder tend to experience lingering depressive or hypomanic symptoms, called subsyndromal symptoms, which tend to be present for more time than full blown episodes [ref]. Subsyndromal depressive symptoms are a cause of disability and reduced quality of life [ref] and thus require treatment just like full-blown episodes.  

Rates and Duration of Bipolar Episodes

As a general rule, people with Bipolar Disorder experience Major Depressive Episodes as well as subsyndromal depressive symptoms far more frequently than Manic or Hypomanic Episodes and symptoms.  Depression is three times more common than Mania or Hypomania in Bipolar I Disorder, and close to 40 times more frequent than Hypomania in Bipolar II Disorder [ref].  The depressive phase is chronic in 20% of cases of Bipolar Disorder [ref]. 

These facts are important to note, given that Major Depressive Episodes and depressive symptoms cause more disability and reduced quality of life than Hypomanic or Manic Episodes [ref], and along with Mixed Episodes are a principal cause of suicide attempts [ref, ref]. 

Left untreated, Bipolar episodes (Major Depressive, Hypomanic, Manic or Mixed) last an average of about 4 months [ref], but these estimates can vary considerably for different individuals and at different points in time.  With treatment, Manic Episodes last an average of 6 weeks, Depressive Episodes an average of 11 weeks, and Mixed Episodes and average of 17 weeks [ref].

The Kindling Effect and Bipolar Disorder

When a person first starts to manifest Bipolar Disorder, their mood episodes (Major Depressive, Hypomanic, Manic or Mixed) tend to happen following stressful life events [ref]. However, over the years, each new mood episode that the person experiences seems to increase their chances of having still more episodes in the future, and these subsequent episodes tend to occur more spontaneously, that is, less and less related to any life stressors.

This is a phenomenon known as kindling, and it implies that the more episodes that a person endures, the more entrenched and automatic the condition becomes [ref]. There is evidence of physical changes that occur in the brain as a result of repeated mood episodes, which may explain this phenomenon [ref, ref].   This suggests that it is very important to provide effective treatment for a person's Bipolar Disorder early in the course of the illness so as to prevent as much as possible the occurrence of multiple episodes.