Depression is a complex mental disorder that can be caused by a variety of factors. It is often said that depression is the result of a chemical imbalance, but research suggests that it is more complicated than that. Genetics, stressful life events, and medical conditions can all contribute to the development of depression. Genetics play an important role in determining who is at risk for depression.
Estimates suggest that depression is approximately 40% determined by genetics. Studies of twins, adoption and family have linked depression to genetics. While studies suggest that there is a strong genetic component, researchers are not yet sure of all genetic risk factors for depression. Stressful life events can also be a cause of depression.
High levels of the hormone cortisol, which are secreted during periods of stress, may affect the neurotransmitter serotonin and contribute to depression. Disruptive or stressful life events, such as grief, divorce, illness, dismissal, and work or financial concerns, may be the cause of depression for some people. Medical conditions can also be a factor in the development of depression. The stress of having a chronic illness can trigger an episode of major depression.
In addition, certain diseases, such as thyroid disorders, Addison's disease, and liver disease, can cause symptoms of depression. It is important to remember that no single cause of depression acts in isolation. A number of different forces are thought to interact to cause depression. Genetics can increase your risk, and environmental influences can determine your likelihood of developing depression.