Depression - Prevalence

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Prevalence

Major depressive disorder affects approximately 6.7% (15 million) of the US population aged 18 and older in a given year. It is the leading cause of disability in the United States for individuals aged 15 to 44 (Kessler, 2005; World Health Organization, 2004).

Clinical depression affects about 16% of the population on at least one occasion in their lives. The mean age of onset, from a number of studies, is in the late 20s. About twice as many females as males report or receive treatment for clinical depression, though this imbalance is shrinking over the course of recent history; this difference seems to completely disappear after the age of 50 - 55, when most females have passed the end of menopause. Clinical depression is currently the leading cause of disability in the US as well as other countries, and is expected to become the second leading cause of disability worldwide (after heart disease) by the year 2020, according to the World Health Organization.

According to the National Institutes of Mental Health, in any given year, major depression afflicts nearly 10 million Americans over the age of 18, or about 5% of the population. When dysthymia (chronic mild depression) is included in the head count, the numbers rise to 18.8 million American adults, or about 9.5% of the population (Narrow 1998). Nearly twice as many women as men suffer from major depression each year (Narrow 1998). If you have just one episode of major depression, there's a 50/50 chance you'll have more, perhaps as many as one or two a year. Millions of depression cases are never diagnosed or treated. Untreated, major depression may last for 6 months to a year, with recurrences becoming more frequent and severe. Without treatment, dysthymic disorder (mild depression) is so persistent that periods of normal mood may last only a few weeks at a time. Major depression is the leading cause of disability in the U.S. Depressed mood ranks just behind high blood pressure as the most common chronic condition doctors see (Wells et al. 1996). Depression costs our society an estimated $44 billion a year, including $23 billion for lowered productivity and absenteeism at work, and $12.3 billion for medical and psychiatric care. Every year thousands of people commit suicide. In 1997, 30,535 people committed suicide, partly or largely as a result of depression, costing taxpayers billions of dollars.

n a recent replication of the National Comorbidity Survey (NCS-R), 9282 individuals aged 18 years and older completed a face-to-face survey using a diagnostic interview guided by the World Health Organization (WHO) World Mental Health Survey Initiative version of the Composite International Diagnostic Interview (WMH-CIDI). Results showed that MDD (6.7%) ranked third in overall prevalence after specific phobia (8.7%) and social phobia (6.8%) when specific disorders were considered. When disorders were assessed according to severity, mood disorders had the highest percentage of serious classifications (45%) as compared with anxiety disorders (22.8%). Severity was also strongly associated with comorbidity. The authors noted that the study under-represented the homeless, individuals in institutions, and non-English speakers. The survey also did not include all DSM-IV diagnoses such as schizophrenia and other nonaffective psychoses. The authors noted that lay administration and the potential for under-reporting were further limitations of the study. However, they also noted that the NCS-R results were consistent with previous epidemiological surveys (Kessler, 2005).

For depression to be considered chronic, full criteria for an episode of major depression must be met without interruption for the preceding 2 years or longer. A number of factors may predispose individuals to chronic depression, including early onset, comorbidity, chronic medical illness, intrapersonal factors, social factors, and either lack of or inadequate treatment (Riso, 2002). Early life trauma, such as child abuse or neglect, is also related to chronic or recurrent episodes of clinical depression (Bifulco, 2000).

Chronic major depression (CMD) is a subtype of MDD. Chronic major depression accounts for 30% to 35% of all depression and is associated with high rates of psychosocial and physical impairment (Keller, 1995a, 1995b). Chronic major depression is also associated with high rates of comorbidity with other mental illnesses, in particular anxiety disorders, substance abuse, and personality disorders, as well as medical disorders such as coronary artery disease (National Institute of Mental Health, 2002; Keller, 1995a; McCullough, 2000; Russell, 2003).

A number of strategies can be used to help prevent chronic forms of depression. These include early recognition and vigorous treatment, increased and improved retention, efforts aimed at producing remission, measurement and monitoring of outcomes, and prevention of relapse (Riso, 2002).

Despite the prevalence of MDD in the US adult population, many cases go unrecognized, and even those patients who are diagnosed often receive inadequate care. Some individuals diagnosed with depression never initiate therapy, and others who do fail to complete an adequate treatment course (Saver, 2007; Keller, 1995b; Kessler, 2003; Horwath, 1992). Patients with chronic depression who do not receive appropriate therapy may experience a variety of problems that can negatively affect their ability to function and quality of life. These individuals may suffer from emotional dysregulation, poor sociability patterns, feelings of helplessness, poor coping skills, and submissive and/or hostile-submissive interpersonal style (McCullough, 2000).

Key texts

Papers

• Blazer, RC et al (1994) The prevalence and distribution of major depression in a national community sample: the National Comorbidity Survey. Am J Psychiatry ; 151:979-986 Abstract

Additional material

Papers

• Lehtinen,V & Joukamaa M(1994) Epidemiology of depression: prevalence, risk factors and treatment situation.- Acta Psychiatr Scand Suppl, PMID 8053370