As with many other diseases, bipolar disorder does not have one specific cause, but is brought on by several contributing factors.
Studies have shown that bipolar disease is significantly more likely to affect people who have a close relative who suffers from it. That does not mean that a person will undoubtedly have the disorder if one of their parents is affected by it, nor does it mean that the disorder is definitely passed on to the children.
There is no definitive and unequivocal explanation about the role of the brain and neurotransmitters.
The disease has been associated with low or high levels or incorrect ratios of neurotransmitters like dopamine, norepinephrine, and serotonin in various parts of the brain. The disorder has also been linked to excessive levels of the stress hormone cortisol, or the increased sensitivity of neuron receptors in certain regions of the brain.
Studies have also shown a link to thyroid disorders.
Brain scans have shown functional changes associated with bipolar disorder in the frontal and temporal lobes and the basal ganglia.
Differences in the circulation and the structure of the regions of the brain which regulate mood and impulse control have also been demonstrated.
One of the key symptoms of the mania and depression phases is disordered sleep rhythms. Insomnia may be a triggering factor for mania, and it can certainly perpetuate or exacerbate that state.
As with many other diseases, stress-inducing life changes, such as changes in close relationships, work, or changing schools, may be a risk factor for bipolar disorder.