The causes of depression are not completely understood, however, this disorder is the result of a variety of psychological and biological risk factors. What this means is that there isn’t a single cause of depression, but rather a number of risk factors that increase the likelihood of a depressive episode. The risk factors may vary considerably from one person to another. So the causes of depression in one person may be very different from the causal factors for someone else.
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Some psychological and environmental risk factors can often be mitigated, which may serve as a means of preventing depressive episodes.
Psychological Risk Factors
One way to understand psychological risk factors for depression is by examining the thinking patterns associated with depression. We all know that positive thinking is generally associated with a happy mood and negative thinking is usually associated with a depressed mood. However, the way we think about ourselves (self-referential thinking) is also a very important driver of our moods.
There is persuasive research evidence that processing of self-referent information is abnormal in depression. For example, persistent negative thinking patterns about the self are known to be associated with depression. Changing these is the basis of one of the most successful psychotherapy treatments for depression: cognitive behavioral therapy (CBT).
In addition to the content of thinking patterns, depression is also associated with excessive self-referential thinking (spending time thinking about the self) as well as a specific type of thinking known as ruminative thinking. Ruminative thinking is analytical thinking, and for those with depression, it means excessively analyzing and thinking about one’s symptoms. Investigating one’s symptoms could result in finding ways to feel better, but it often results in the exact opposite. This is because ruminative thinking usually involves automatic thinking patterns that are illogical and worry-based rather than solution-focused. For example, “I probably won’t be able to enjoy the party tomorrow,” rather than, “I should take a walk right now because that always helps me to feel better.” Some psychological treatments for depression focus on the recognition and changing of ruminative thinking patterns.
Biological Risk Factors
Multiple studies have convincingly demonstrated that depressive disorders are partly caused by genetic, or inherited, factors. The evidence indicates that what is inherited is a risk for developing a depressive disorder rather than the actual illness. First-degree relatives of those with depressive illness have a greatly increased risk of developing a depressive disorder and a moderately increased risk of developing bipolar disorder. However, depression can occur in the absence of a family history of this illness.
As with risk factors, causes of depression can be divided into psychological and biological categories. Psychological causes include the thinking patterns described above as well as stress and psychological trauma.
There are a number of biological factors that can cause depression. Over the years, one of the main theories of the cause of depression has been the monoamine hypothesis. This is sometimes referred to as a brain chemical imbalance and refers to abnormalities of neurotransmitters (chemicals that carry messages in the brain). This hypothesis, originally proposed in 1965, holds that two monoamine neurotransmitters (serotonin and norepinephrine) and possibly a third (dopamine) are deficient in depression. Extensive research over the years clearly establishes the role these neurotransmitters play in depressive disorders. However, it is almost certainly more complicated than deficits of specific neurotransmitters.
More recent hypotheses of the causes of depression include chronic inflammation and disruptions of brain circuit function.
Studies of prevention of depression have focused primarily on preventing recurrence after one has experienced an initial depressive episode. One important strategy is ensuring that the initial episode is adequately treated and that there is full remission of all symptoms. Other prevention strategies include ongoing maintenance treatment with antidepressant medication and/or psychotherapy. Mindfulness-based cognitive therapy (MBCT) has been shown to be effective in prevention relapse. This intervention is discussed in the Alternative Medicine for Depression section.