What Causes Major Depressive Disorder?

The exact causes of MDD are unknown, although biological, psychological, and social factors all likely play important roles in the illness:

Genes

In some families, MDD affects someone in every generation, suggesting a biological (genetic) component to the disorder. However, MDD also happens to people with no family history of depression. So, in some cases, a vulnerability to MDD may be inherited and in other cases not. Genes are probably not the whole story. Whether inherited or not, MDD, and especially chronic MDD has been associated with some fairly specific changes in brain chemistry and structures.

Stress

Stressful life events such as the death of a loved one, relationship problems, and marital problems, problems at work, financial problems, or unemployment can trigger a depressive episode. Sometimes even positive life changes such as marriage, new relationship, job promotion, or moving can trigger a depressive episode.

The brain changes in MDD may be related to the brain's response to stress (or bad experiences) in early life. Later in life, this may cause the brain to react to one or more new negative events. Without any negative life events, people may avoid the risk for developing depression.

Neurotransmiters

Neurotransmitters are chemicals that convey or inhibit communication between nerve cells. Research has implicated a number of transmitter systems in MDD including serotonin, norepinephrine and dopamine.

Brain Structures

The use of modern brain imaging techniques has shown brain structure changes associated with MDD in a number of brain areas (including the limbic, orbital and prefrontal cortex, amygdala, ventral striatum, and hippocampus).

Psychological Factors and Personality

Some people with certain characteristics seem to be more likely to suffer from MDD. Some of these personality types include: people with low self-esteem, people who are pessimistic, those who self-criticize, perfectionists, and people who are easily overwhelmed by stress. These characteristics sometimes represent a psychological predisposition to depression. Sometimes they represent early symptoms of MDD.

Other Factors

Other events associated with MDD include childbirth, menopause and seasonal changes.

Medical illnesses

Stroke, heart attack, cancer, Parkinson's disease, infectious diseases such as influenza and hepatitis, and some hormonal disorders can cause depression. Depression complicates these medical illnesses because the depression makes people less able to look after themselves properly and work towards recovery and getting back to health.

Medications

Some medications such as antihypertensive medication, oral contraceptives and corticosteroids can cause depressive symptoms.

Most often it's likely that some combinations of biological, psychological, social and environmental factors are involved in the onset of an initial episode of MDD. Once a person has had one episode of MDD, new stressful events can trigger future episodes. While most people can identify a "trigger" for a depressive episode, it is sometimes difficult or impossible to identify an event or stress. Sometimes depression seems to just happen out of nowhere and come "out of the blue."

Major Depressive Disorder in Women

Approximately twice as many women as men get diagnosed with MDD (major depressive disorder). Hormonal changes such as menstrual cycle changes, pregnancy, miscarriage, postpartum changes, pre-menopause, and menopause may contribute to the higher rate of MDD in women, but these differences between men and women are not the whole story.

Women seem to be more vulnerable to depression following childbirth and it's very common for new mothers to show some symptoms of depression. It may be that the hormonal and physical changes associated with childbirth and the post-partum period and the stress associated with such an important life event are factors that can result in postpartum depression. However, MDD following the birth of a child is not normal. It is a serious problem that requires help right away.

While hormonal factors may be important, it may be that MDD is more common in women because women are simply under more stress than men. Women often have responsibilities to work outside the home and do most of the work that needs to be done inside the home, including caring for children and aging parents, and maintaining relationships. In addition, women have the stress associated with being a single parent more often than men.

Another reason why women may be more likely to become depressed compared to men is that women's sense of self seems to be largely derived from their relationships. In order to preserve their relationships (and hence self-esteem) women are more likely to initiate and maintain relationships in self-sacrificing ways making them particularly vulnerable to depression. Also, in times of conflict, women are more likely to ruminate or think "over and over again" about the conflict. Thinking too much about something negative often leads to increased feelings of depression.

Finally, as compared to men, women may be more likely to admit to being depressed and doctors may be more likely to ask women about depression.

Major Depressive Disorder in Men

Although it may be that fewer men than women may have MDD, at any one time at least 2-3% of men are affected by it. MDD in men is just as serious a problem. In fact, although more women attempt suicide, the rate of completed suicide is four times higher in men. As compared to women, men are less likely to admit to having the symptoms of MDD, and doctors are less likely to ask men about depression. Depressed men are more likely to say that they feel irritable, angry, and discouraged, rather than describe themselves as hopeless and helpless or sad. This may be one of the reasons why depression is harder to recognize in men as compared to women.

Even when men know that they're depressed, men may be less likely to ask for help. Men often attempt to deal with their depression by working all the time or by abusing alcohol or drugs. Sometimes it takes the encouragement and support of concerned family members and friends to convince men that depression as a real medical illness and that effective treatments are available.

Major Depressive Disorder in the Elderly

Many people think that it is normal for elderly people to be depressed. In fact, nothing could be further from the truth. Most older people enjoy happy, active and interesting lives. Unfortunately, when an elderly person gets depressed, people often dismiss the symptoms as a "normal" part of aging, as they assume that getting older in and of itself must be "depressing." Once again, this is simply not true.

Untreated depression in the elderly is a serious problem that causes great suffering. One difficulty in identifying depression in the elderly is that many of the symptoms of depression (e.g., sleep difficulties, fatigue, appetite disturbance) can mimic certain medical conditions. Sometimes depression in the elderly is mistaken for Alzheimer's Disease or dementia.