Bipolar disorder is a serious but treatable mental illness affecting 5.7 million adults in the United States, about 2.6 percent of the population over 18 years of age, according to the National Institute of Mental Health. It used to be called manic-depressive disorder, due to the disruptive mood swings of the illness.

Brain differences

People with bipolar disorder appear to have brain differences, according to the Mayo Clinic. Newer technologies, such as PET scans and newer types of MRI, are leading to new findings with bipolar disorder, as well as other mood disorders.

Neurotransmitters

Neurotransmitters are chemicals in the brain that seem to play an important role in mood and emotion, and influence mood disorders such as bipolar disorder.

Hormones

Hormones that are not in balance may cause or trigger bipolar disorder, according to the Mayo Clinic.

Genetics

Having a blood relative, such as a parent or sibling, with bipolar disorder increases the likelihood of having the disorder, making it 4 to 6 times more likely than in someone without such genetic factors.

Environment

Environmental factors that may play a part in developing bipolar disorder include stress, abuse, experiencing a traumatic event, big life changes and substance abuse.

Combinations

The most likely scenario for developing bipolar disorder is not a factor from just one category, but rather a combination of factors, such as a genetic predisposition combined with environmental or physical factors.

Source:

Mayo Clinic: Bipolar Disorder: Causes

National Institute of Mental Health: Bipolar Disorder

National Institute of Mental Health: The Numbers Count