The exact cause of bipolar disorder is not fully understood. However, experts believe that a number of different factors act together and make a person more likely to develop the condition. These are thought to be a complex mix of environmental, cognitive, biological and genetical factors.
- Stressful life events often occur prior to first onset and recurrences of mood episodes, particularly in the area of work and relationships.
It is thought that these life events can trigger mood episodes among people with bipolar disorders by disrupting their daily social rhythms (e.g. meal times, sleep-wake times), which destabilises their circadian rhythms.
Circadian rhythms are physical, mental and behavioural changes that follow a roughly 24-hour cycle, responding primarily to light and darkness. Your circadian rhythm tells you when to sleep, eat, work, play etc.
Other types of life events that have been associated with triggering mood episodes among people with bipolar disorder are life events involving goal-directed behaviour.
It is thought that people with bipolar disorder have a hypersensitive Behavioral Approach System (BAS). BAS regulates your motivation and goal-directed behaviour to attain rewards. It is suspected that the BAS in people with bipolar disorder responds with too many positive emotions, energy and motivation (i.e., mania/hypomania) to events involving high incentive motivation and goal striving or attainment and with too negative emotions, energy and loss of pleasure (i.e., depression) to events involving uncontrollable loss and failure.
- Environments characterised by high criticism and emotional over-involvement from family and friends have been associated with longer recovery time, greater likelihood of relapse and more severe impairment due to the disorder. In contrast, positive social support from family and friends can buffer against the negative effects of stress or directly enhance functioning for people with bipolar disorder.
Negative cognitive styles and negative views of the self and the world increases the risk of mood episodes among people with bipolar disorder.
In particular, negative cognitive styles such as self-criticism (e.g. "I have a difficult time accepting weaknesses in myself") and perfectionism (e.g. "If I fail partly, it is as bad as being a complete failure") is associated with greater risk for manic/hypomanic and depressive episodes.
There are subtle differences in the average size activation and network connections between some brain structures in people with bipolar disorder. While brain structure alone may not cause it, there are some conditions in which damaged brain tissue can predispose a person. In some cases, concussions and traumatic head injuries can increase the risk of developing bipolar disorder.
Family studies and twin studies suggest a genetic basis for bipolar disorder. The lifetime risk of bipolar disorder in first-degree relatives of a bipolar patient is 40–70% for a monozygotic twin and 5–10% for all other first-degree relatives.
If one parent has bipolar disorder, there's a 10% chance that their child will develop the illness.
If both parents have bipolar disorder, the likelihood of their child developing bipolar disorder rises to 40%.
However, just because one family member has the illness does not mean that other family members will develop bipolar disorder. We do not know how exactly genetics influence the development of bipolar disorder, indicating the interaction of several genes, and a strong environmental influence.
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