Episodes of recurrent depression may lead to adverse economic, interpersonal, and medical consequences. For example, the impact of depression on a family can be detected not only during the depressive episode, but also years after symptomatic remission. Impairment of vocational functioning may similarly persist despite response to treatment. Complications such as alcoholism or substance abuse also may develop during an untreated depressive episode. In addition, depression complicates the course of chronic general medical illnesses such as diabetes and atherosclerotic heart disease.
Most initial depressive episodes are temporarily related to stress, which highlights the role of stress-diathesis vulnerability interactions, suggesting that certain critical factors impinge on a person’s life, which may in turn become a catalyst for the development of an illness in those who are genetically predisposed.
Women have about 1.7 times the lifetime risk of developing a major depressive episode.Other relevant risk factors include a family history of affective disorder or alcoholism, a pattern of cognitive distortions, personality disorders, chronic medical problems, and a history of early trauma or abuse.
The relationship between stress and the onset of depressive episodes appears to become less pronounced in more highly recurrent episodes, and new episodes often begin to appear “out-of-the-blue.” Some researchers have suggested that the apparent tendency for recurrent depressive episodes to become autonomous results from changes in brain stress-response mechanisms.
People with recurrent depression, for example, have a greater likelihood of hypothalamic-pituitary-adrenocortical dysregulation and more pronounced alterations of sleep neurophysiology.Other recurrent disorders have a seasonal pattern, with fall and winter more commonly associated with depressive episodes. Although the precise mechanism of seasonal vulnerability has not been elucidated, these recurrent depressions are thought to be triggered by changes in the length of the photoperiod (period of available sunlight).