What Causes Depression?

What causes depression? Although there are many complex factor involved in the development of a depressive episode, scientists have found that a central factor is an imbalance of important chemicals in the brain. This means that bipolar depression is, at root, a physical illness that causes symptoms identified as a mental illness. Indeed, one important court case already ended in a ruling that, for insurance purposes, said bipolar disorder is a physical illness.

Neurotransmitters

To understand the causes of bipolar depression, you must first understand that there are chemicals in the brain called neurotransmitters. These chemicals transmit "messages" from one nerve cell to another. If this process is not working correctly, depression can result. For more, see Neurotransmitters.

Specific Neurotransmitters in Bipolar Depression

The neurotransmitters that play a part in bipolar depression are serotonin, norepinephrine and dopamine. Imbalances of these chemicals have been connected to depression. In bipolar disorder, these and other neurotransmitters are also a factor in producing mania and hypomania.

Why do some people have problems with low (or both low and high) levels of these chemicals? Genetics plays a big part - there is no doubt that both bipolar disorder and Major Depressive Disorder run in families. Researchers are continually working to identify genes that are common to people with bipolar disorder. But that's not the whole story, either.

Biological Stress Factors in Bipolar Depression

Some scientists believe that people may be born with the genes for bipolar disorder and then stress sets it off. (See What Causes Bipolar Disorder?.) Indeed, the stress hormone cortisol has been seen to be a factor in depression. Stress increases the level of cortisol in the body, which causes the levels of serotonin and dopamine to drop. In people who have chronic or bipolar depression, cortisol levels may stay high even when stress isn't present.

Stress and Triggers in Bipolar Depression

Bipolar depression can and frequently does occur spontaneously, thanks to the genetic and biological factors. But a bipolar depressive episode can also be set off by an event or circumstances which are sometimes called triggers.

A person who has never before suffered from depression may become depressed after an event like a death in the family, job loss, divorce, etc., and in time - with or without treatment, depending on the circumstances and severity - return to his or her normal mood. The same kinds of events can also trigger depression in a person who has bipolar disorder.

Someone with bipolar disorder may also find that smaller things can trigger depressive episodes. Reading a book that makes you sad, talking to someone who's depressed, a poor grade on a paper you thought was sure to get an A, even catching a cold might contribute to a depressive episode. Some people are triggered by noise, disruption in sleep, travel, etc. Because depressive episodes can be triggered, it's a good idea to identify your triggers and, if possible, discuss them with the doctor or therapist who treats your bipolar disorder. Once you know what triggers your bipolar depression, you may be able to find ways to deal with the triggers themselves to head off some depressive episodes.

_Sources:

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_{Durand, V. M. & Barlow, D. H. (2000). Abnormal Psychology: An Introduction. Scarborough, Ontario: Wadsworth.}

_{"Genetics and Major Psychiatric Disorder: Empiric Risks." National Coalition for Health Professional Education in Genetics. April 2004. 15 Sept 2009. (Unavailable)}

_{McGuffin, P., et al. The heritability of bipolar affective disorder and the genetic relationship to unipolar depression. Arch Gen Psychiatry. 2003 May;60(5):497-502. 12 Sept 2009.}