Understanding the Causes of Bipolar Disorder

Whether you can be born with bipolar disorder remains an unresolved question. Studies suggest a genetic component to this mental illness, but DNA isn't the only reason people develop bipolar disorder. Most researchers agree that brain and environmental factors probably contribute as well.

Genetic Factors

Considerable research in multiple families, adoption, and twin studies has focused on the question of bipolar disorder's heritability—whether bipolar disorder can be inherited.

This is important for genetic theories because identical twins occur when one fertilized egg splits in two, meaning that they share the same genetic material. Fraternal twins, on the other hand, come from separate fertilized eggs, so their inherited genes can be different. There is overwhelming evidence that bipolar disorder can be inherited and that there is a genetic vulnerability to developing the illness.

Brain Function 

When it comes to figuring out exactly what is inherited, the neurotransmitter system has received a great deal of attention as a possible cause of bipolar disorder. A link exists between neurotransmitters and mood disorders, and drugs that alter these transmitters also treat mood disorders:

In short, researchers are quite certain that the neurotransmitter system is at least part of the cause of bipolar disorder, but further research is still needed to define its exact role.

Societal Factors

Mood episodes in bipolar disorder can both be set off by a stressful event or circumstances, but can and frequently do occur spontaneously.

How stress triggers a bipolar episode is not fully understood, but scientists believe that the stress hormone cortisol plays a role. Stress increases the level of cortisol in the body, which causes alterations in how the brain functions and communicates. In fact, in people who have depression or bipolar disorder, cortisol levels may stay high even when stress isn't present.

Stressful life events can range from a death in the family to the loss of a job, and from the birth of a child to a move.

Stress may stem from a variety of experiences. It cannot be precisely defined, since one person may perceive an event as extremely stressful while another individual encountering the same event may not experience much stress. 

Environmental Triggers

For Depressive Episodes

Once someone experiences bipolar disorder, small stresses may trigger depressive episodes.

Examples of bipolar depressive episode triggers include:

• sleep deprivation or disruption
• stressful life events
• general stress
• physical injury or illness
• menstruation
• lack of exercise

For Manic Episodes

While triggers for manic and depressive episodes can be the same, there are some that are specific to manic or hypomanic episodes. According to a 2012 study in the Journal of Affective Disorders, unique triggers of manic or hypomanic episodes include:

• falling in love
• recreational stimulant use
• starting a creative project
• late night partying
• vacationing
• loud music

In addition, the postpartum period and the use of an antidepressant, like an SSRI, may also trigger a manic or hypomanic episode.

The Diathesis-Stress Model

When we look for the cause of bipolar disorder, the best explanation according to research published in 2015 is what is termed the "Diathesis-Stress Model."

The word diathesis, in simplified terms, refers to a physical condition that makes a person more susceptible than usual to certain diseases. Thus the Diathesis-Stress Model says that each person inherits certain physical vulnerabilities to problems that may or may not appear depending on what stresses occur in their life.

So the bottom line is that if you have bipolar disorder, you were likely born with the possibility of developing this disorder and something in your life triggered it. However, scientists could refine that theory tomorrow. The one sure thing is that they won't give up looking for answers.