Causes of Depression

Some depressions seem to come out of the blue, even when things are going well.

Others seem to have an obvious cause: a marital conflict , financial difficulty, or some personal failure.

Yet many people with these problems do not become deeply depressed.

Most psychologists believe depression results from an interaction between stressful life events and a person’s biological and psychological vulnerabilities.

Biological Factors
Depression runs in families.

By studying twins, researchers have found evidence of a strong genetic influence in depression.

Genetically identical twins raised in the same environment are three times more likely to have depression in common than fraternal twins, who have only about half of their genes in common.

In addition, identical twins are five times more likely to have bipolar disorder in common.

These findings suggest that vulnerability to depression and bipolar disorder can be inherited.

Adoption studies have provided more evidence of a genetic role in depression.

These studies show that children of depressed people are vulnerable to depression even when raised by adoptive parents.

Genes may influence depression by causing abnormal activity in the brain.

Studies have shown that certain brain chemicals called neurotransmitters play an important role in regulating moods and emotions.

Neurotransmitters involved in depression include norepinephrine, dopamine, and serotonin.

Research in the 1960s suggested that depression results from lower than normal levels of these neurotransmitters in parts of the brain.

Support for this theory came from the effects of antidepressant drugs, which work by increasing the levels of neurotransmitters involved in depression.

However, later studies have discredited this simple explanation and have suggested a more complex relationship between neurotransmitter levels and depression.

An imbalance of hormones may also play a role in depression.

Many depressed people have higher than normal levels of hydrocortisone (cortisol), a hormone secreted by the adrenal gland in response to stress.

In addition, an underactive or overactive thyroid gland can lead to depression.

A variety of medical conditions can cause depression.

These include dietary deficiences in vitamin B6, vitamin B12, and folic acid (see Vitamin); degenerative neurological disorders, such as Alzheimer’s disease and Huntington’s disease (see Chorea); strokes in the frontal part of the brain; and certain viral infections, such as hepatitis and mononucleosis.

Certain medications, such as steroids, may also cause depression.

Psychological Factors
Psychological theories of depression focus on the way people think and behave.

In a 1917 essay, Austrian psychoanalyst Sigmund Freud explained melancholia, or major depression, as a response to loss—either real loss, such as the death of a spouse, or symbolic loss, such as the failure to achieve an important goal.

Freud believed that a person’s unconscious anger over loss weakens the ego, resulting in self-hate and self-destructive behavior.

Cognitive theories of depression emphasize the role of irrational thought processes.

American psychiatrist Aaron Beck proposed that depressed people tend to view themselves, their environment, and the future in a negative light because of errors in thinking.

These errors include focusing on the negative aspects of any situation, misinterpreting facts in negative ways, and blaming themselves for any misfortune.

In Beck’s view, people learn these self-defeating ways of looking at the world during early childhood.

This negative thinking makes situations seem much worse than they really are and increases the risk of depression, especially in stressful situations.

In support of this cognitive view, people with “depressive” personality traits appear to be more vulnerable than others to actual depression.

Examples of depressive personality traits include gloominess, pessimism, introversion, self-criticism, excessive skepticism and criticism of others, deep feelings of inadequacy, and excessive brooding and worrying.

In addition, people who regularly behave in dependent, hostile, and impulsive ways appear at greater risk for depression.

American psychologist Martin Seligman proposed that depression stems from “learned helplessness,” an acquired belief that one cannot control the outcome of events.

In this view, prolonged exposure to uncontrollable and inescapable events leads to apathy, pessimism, and loss of motivation.

An adaptation of this theory by American psychologist Lynn Abramson and her colleagues argues that depression results not only from helplessness, but also from hopelessness.

The hopelessness theory attributes depression to a pattern of negative thinking in which people blame themselves for negative life events, view the causes of those events as permanent, and overgeneralize specific weaknesses as applying to many areas of their life.

Stressful Events
Psychologists agree that stressful experiences can trigger depression in people who are predisposed to the illness.

For example, the death of a loved one may trigger depression.

Psychologists usually distinguish true depression from grief, a normal process of mourning a loved one who has died.

Other stressful experiences may include divorce, pregnancy, the loss of a job, and even childbirth.

About 20 percent of women experience an episode of depression, known as postpartum depression, after having a baby.

In addition, people with serious physical illnesses or disabilities often develop depression.

People who experience child abuse appear more vulnerable to depression than others.

So, too, do people living under chronically stressful conditions, such as single mothers with many children and little or no support from friends or relatives.