Depression Causes and Risk Factors
The cause of major depressive disorder is a combination of brain chemistry, family history, and psychosocial environment. It is not certain which of these factors dominates, but abnormal levels of the neurotransmitters norepinephrine, serotonin, and dopamine are closely linked with depression. Thus, the cause of depression is often attributed to a "chemical imbalance." These neurotransmitters play important roles in how we experience pleasure and moods.
Other physiological changes that accompany depression may result in irregular hormone levels in the brain. There is, however, little evidence to support the idea that abnormal hormone levels cause depression.
Computed tomography (CT scan), which produces images of the brain, may reveal enlarged lateral ventricles (structures in the brain that produce cerebrospinal fluid) in some people who suffer from depression. These test results suggest that abnormalities in brain structure may be a factor in depression.
Genetic Risk Factors for Depression
Statistics show that the children of parents who suffer from depression are more likely to develop the disorder themselves. A person has a 27 percent chance of inheriting a mood disorder from one parent, and this chance doubles if both parents are affected. Studies of the occurrence of depression in twins show a 70 percent chance for both identical twins to suffer from depression, which is twice the rate of occurrence in fraternal twins.