Scientists agree that there is no single cause of bipolar disorder, but many factors interact to cause or increase risk of the disorder.
Studies indicate that first degree biological relatives (parent or sibling) of individuals with bipolar disorder have higher rates of having the condition themselves compared to the general population. People with a first degree relative with bipolar disease have a 5 to 10 percent increased risk of being diagnosed with bipolar disorder. There is a 40 to 70 percent risk of bipolar disorder in an identical twin if one twin is diagnosed with the disease, suggesting there is a significant genetic component to the development of bipolar.
People between the ages of 15 and 25 are at a greater risk of bipolar disorder, with half of cases being diagnosed before the age of 25. However, bipolar disorder has been diagnosed in children as young as 6 years old, and people have developed symptoms in their 30s and 40s.
Bipolar II disorder is more common in women than in men. However, bipolar I disorder is equally prevalent in both sexes.
Environmental and Lifestyle Factors
Scientists believe that environmental factors like stress, abuse, experiencing a traumatic event, or becoming addicted to alcohol or other substances may prime the brain for development of bipolar disease.