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% 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.
Psychosocial and Environmental Risk Factors for Depression
Depression is more common in people who have a history of trauma, sexual abuse, physical abuse, physical disability, bereavement at a young age, alcoholism, and insufficient family structure. In adults, the loss of a spouse is the most common cause of a depressive episode. Women are at increased risk for depression during and within the first few months after pregnancy (called postpartum depression). Chronic depression may be more common in areas afflicted with war, natural disasters, poverty, or neglect.
There is no evidence that depression strikes certain personality types more than others. However, temperament and perception of self and others may be predisposing factors. The following cognitive factors (which affect judgment and perception) are associated with depression:
- Chronic low self-esteem
- Distorted perception of others' views
- Distorted sense of life experience
- Inability to acknowledge personal accomplishment
- Negative idea of self
- Pessimistic outlook
- Quick and exaggerated temper
Age & Depression Risk
Although depression can occur at any age, its onset is typically between the ages 24 and 44. Later onset may correlate with the absence of a family history of depression. Fifty percent of people with major depressive disorder experience their first episode of depression at about age 40, but this may be may be shifting to the 30s. Studies find that the rate of incidence is higher among middle-aged people.
Teenagers are at risk for depression. The evidence is in teen suicide rates, which are increasing yearly. The growing rate of depression in this group may reflect growing pressure on young people to attend college and meet the high expectations of their peers and parents. Problems with self-esteem may result from failure or disinterest in meeting these expectations. Low self-esteem can lead to a negative perspective of life and depression.
Gender & Depression Risk
Major depressive disorder affects 10% of men and 20% of women. Hormonal differences may put women at a higher risk for depression. Hormone levels are influenced by pregnancy, and many women experience depression after giving birth.
The disparity between rates of depression in men and women may reflect behaviors based on learned gender roles. Learned helplessness and socioeconomic stressors may result in depression in women. The socialization of men, which demands self-sufficiency and emotional toughness, may cause depression in men and may prevent them from seeking treatment.
Race and Class & Depression Risk
Although there does not seem to be a correlation between depression and race or class, depression is diagnosed more often in Caucasians from the middle and upper classes. Caucasian psychiatrists may not recognize the condition in African Americans, Asians, or Latinos as frequently as it occurs. Differences in socioeconomic background may prevent psychiatrists from observing depression in people from lower economic classes; they simply cannot afford to seek medical attention for nonemergencies.