0.6-1% of adults will have a manic episode during their lifetime in Canada (Health Canada)
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The cause of bipolar disorder is unclear, but hereditary, biological, and psychological factors may play a part. For example, the incidence of bipolar disorder among relatives of affected patients is higher than in the general population and highest among maternal relatives. The closer the relationship, the greater the susceptibility. Children with one affected parent have a 25% chance of developing bipolar disorder; children with two affected parents, a 50% chance. The incidence of this illness in siblings is 20% to 25%; in identical twins, the incidence is 66% to 96%.
Although certain biochemical changes accompany mood swings, it isn’t clear whether these changes cause the mood swings or result from them. In mania and depression, intracellular sodium concentration increases during illness and returns to normal with recovery.
Patients with mood disorders have a defect in the way the brain handles certain neurotransmitters — chemical messengers that shuttle nerve impulses between neurons. Low levels of the chemicals dopamine and norepinephrine, for example, have been linked to depression, whereas excessively high levels of these chemicals are associated with mania.
Changes in the concentration of acetylcholine and serotonin may also play a role. Although neurobiologists have yet to prove that these chemical shifts cause bipolar disorder, it’s widely assumed that most antidepressant medications work by modifying these neurotransmitter systems.
New data suggest that changes in the circadian rhythms that control hormone secretion, body temperature, and appetite may contribute to the development of bipolar disorder.
Emotional or physical trauma, such as bereavement, disruption of an important relationship, or a serious accidental injury, may precede the onset of bipolar disorder; however, bipolar disorder commonly appears without identifiable predisposing factors.
Manic episodes may follow a stressful event, but they’re also associated with antidepressant therapy and childbirth. Major depressive episodes may be precipitated by chronic physical illness, psychoactive drug dependence, psychosocial stressors, and childbirth. Other familial influences, especially the early loss of a parent, parental depression, incest, or abuse, may predispose a person to depressive illness. (See Cyclothymic disorder.)
The American Psychiatric Association estimates that 0.4% to 1.2% of adults experience bipolar disorder. This disorder affects women and men equally and is more common in higher socioeconomic groups. It can begin any time after adolescence, but onset usually occurs between ages 20 and 35; about 35% of patients experience onset between ages 35 and 60. Before the onset of overt symptoms, many patients with bipolar disorder have an energetic and outgoing personality with a history of wide mood swings.
Bipolar disorder recurs in 80% of patients; as they grow older, the episodes recur more frequently and last longer. This illness is associated with a significant mortality; 20% of patients commit suicide, many just as the depression lifts.
Source: Professional Guide to Diseases (Eighth Edition), 2005
The term 'prevalence' of Mania usually refers to the estimated population
of people who are managing Mania at any given time.
The term 'incidence' of Mania refers to the annual diagnosis rate,
or the number of new cases of Mania diagnosed each year.
Hence, these two statistics types can differ:
a short-lived disease like flu can have high annual incidence but low prevalence,
but a life-long disease like diabetes has a low annual incidence but high prevalence.
For more information see about prevalence and incidence statistics.
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