What Is Major Depressive Disorder?

According to the DSM-5, the defining symptoms of major depressive disorder (MDD) include “depressed mood most of the day, nearly every day” (feeling sad, empty, or hopeless or appearing tearful to others), and loss of interest and pleasure in usual activities (APA, 2013). In addition to feeling overwhelmingly sad most of each day, people with depression will no longer show interest or enjoyment in activities that previously were gratifying, such as hobbies, sports, sex, social events, time spent with family, and so on. Friends and family members may notice that the person has completely abandoned previously enjoyed hobbies; for example, an avid tennis player who develops major depressive disorder no longer plays tennis (Rothschild, 1999).

To receive a diagnosis of major depressive disorder, one must experience at least a total of five symptoms of the following symptoms for at least a two-week period (in addition to having a depressed mood and a loss of interest in activities); these symptoms must cause significant distress or impair normal functioning, they must be a change from previous functioning, and they must not be caused by substances or a medical condition. These symptoms include:

1. significant weight loss (when not dieting) or weight gain and/or significant decrease or increase in appetite;
2. difficulty falling asleep or sleeping too much;
3. psychomotor agitation (the person is noticeably fidgety and jittery, demonstrated by behaviors like the inability to sit, pacing, hand-wringing, pulling or rubbing of the skin, clothing, or other objects) or psychomotor retardation (the person talks and moves slowly, for example, or talks softly, very little, or in a monotone voice);
4. fatigue or loss of energy;
5. feelings of worthlessness or guilt;
6. difficulty concentrating and indecisiveness; and
7. suicidal ideation: thoughts of death (not just fear of dying), thinking about or planning suicide, or making an actual suicide attempt.

Major depressive disorder (MDD) is considered episodic: its symptoms are typically present at their full magnitude for a certain period of time and then gradually abate. Approximately 50–60% of people who experience an episode of major depressive disorder (MDD) will have a second episode at some point in the future; those who have had two episodes have a 70% chance of having a third episode, and those who have had three episodes have a 90% chance of having a fourth episode (Rothschild, 1999). Although the episodes can last for months, a majority of people diagnosed with this condition (around 70%) recover within a year. However, a substantial number do not recover; around 12% show serious signs of impairment associated with major depressive disorder after five years (Boland & Keller, 2009). In the long term, many who do recover will still show minor symptoms that fluctuate in their severity (Judd, 2012).

Prevalence

Major depressive disorder affected approximately 163 million people in 2017 (2% of the global population).^[1] The percentage of people who are affected at one point in their life varies from 7% in Japan to 21% in France. In most countries, the number of people who have depression during their lives falls within an eight to 18% range. In North America, the probability of having a major depressive episode within a year-long period is 3%-5% for males and eight to 10% for females. Major depression is about twice as common in women as in men, although it is unclear why this is so and whether factors unaccounted for are contributing to this. The relative increase in occurrence is related to pubertal development rather than chronological age, reaches adult ratios between the ages of 15 and 18, and appears associated with psychosocial more than hormonal factors. Depression is a major cause of disability worldwide.

People are most likely to develop their first depressive episode between the ages of 30 and 40, and there is a second, smaller peak of incidence between ages 50 and 60. The risk of major depression is increased with neurological conditions such as stroke, Parkinson’s disease, or multiple sclerosis, and during the first year after childbirth. It is also more common after cardiovascular illnesses and is related more to those with a poor cardiac disease outcome than to a better one. Studies conflict on the prevalence of depression in the elderly, but most data suggest there is a reduction in this age group. Depressive disorders are more common in urban populations than in rural ones and the prevalence is increased in groups with poorer socioeconomic factors, e.g., homelessness.

Causes of Depression

MDD is believed to be a combination of genetic, environmental, and psychological factors. Risk factors include a family history of the condition, major life changes, certain medications, chronic health problems, and substance abuse. About 40% of the risk appears to be related to genetics.^[2]

Figure 2. The biopsychosocial model shows that a variety of factors may influence mental health.

The diathesis-stress model specifies that depression results when a preexisting vulnerability, or diathesis, is activated by stressful life events. The pre-existing vulnerability can be either genetic, implying an interaction between nature and nurture, or schematic, resulting from views of the world learned in childhood.

The biopsychosocial model is an interdisciplinary model that looks at the interconnection between biological, psychological, and social-environmental factors. The model specifically examines how these aspects play a role in topics ranging from health and disease models to human development. Childhood abuse, whether physical, sexual, or psychological, are all risk factors for depression, among other psychiatric issues that co-occur such as anxiety and drug abuse. Childhood trauma also correlates with the severity of depression, lack of response to treatment, and length of illness. However, some are more susceptible to developing mental illness such as depression after trauma, and various genes have been suggested to control susceptibility.

Results of Major Depressive Disorder

Major depressive disorder is a serious and incapacitating condition that can have a devastating effect on the quality of one’s life. The person suffering from this disorder lives a profoundly miserable existence that often results in unavailability for work or education, abandonment of promising careers, and lost wages; occasionally, the condition requires hospitalization. The majority of those with major depressive disorder report having faced some kind of discrimination and many report that having received such treatment has stopped them from initiating close relationships, applying for jobs for which they are qualified, and applying for education or training (Lasalvia et al., 2013). Major depressive disorder also takes a toll on health. Depression is a risk factor for the development of heart disease in healthy patients, as well as adverse cardiovascular outcomes in patients with preexisting heart disease (Whooley, 2006).

Risk Factors for Major Depressive Disorder

Major depressive disorder is often referred to as the common cold of psychiatric disorders. Around 6.6% of the U.S. population experiences major depressive disorder each year; 16.9% will experience the disorder during their lifetime (Kessler & Wang, 2009). It is more common among women than among men, affecting approximately 20% of women and 13% of men at some point in their lives (National Comorbidity Survey, 2007). The greater risk among women is not accounted for by a tendency to report symptoms or to seek help more readily, suggesting that gender differences in the rates of major depressive disorder may reflect biological and gender-related environmental experiences (Kessler, 2003).

Lifetime rates of major depressive disorder tend to be highest in North and South America, Europe, and Australia; they are considerably lower in Asian countries (Hasin, Fenton, & Weissman, 2011). The rates of major depressive disorder are higher among younger age cohorts than among older cohorts, perhaps because people in younger age cohorts are more willing to admit depression (Kessler & Wang, 2009).

A number of risk factors are associated with major depressive disorder: unemployment (including homemakers); earning less than $20,000 per year; living in urban areas; or being separated, divorced, or widowed (Hasin et al., 2011). Comorbid disorders include anxiety disorders and substance abuse disorders (Kessler & Wang, 2009).