Mental disorders more widespread than estimated: study comes as psychiatrists reevaluate diagnostic manual.

Some mental disorders aren't merely common--they're the norm.

Depression, anxiety disorders, alcohol dependence and marijuana dependence affect roughly twice as many people as had been estimated previously, a new study finds. Nearly 60 percent of the population experiences at least one of these mental disorders by age 32, say study directors and psychologists Terrie Moffitt and Avshalom Caspi, both of Duke University in Durham, N.C.

That figure probably gets higher by the time people reach middle age, Moffitt suggests, as additional people develop at least one of these four ailments for the first time.

In a paper published online September 1 and in an upcoming Psychological Medicine, Moffitt and Caspi present results from a study of more than 1,000 New Zealanders assessed for mental disorders 11 times between ages 3 and 32. This study took a prospective approach, following people as they aged, and assessed prevalence rates based on long-term data. Moffitt's team focused most intensively on the period from age 18 to 32, when these disorders typically first start to appear. Earlier prevalence estimates for mental disorders in the United States and New Zealand relied on self-reports and therefore adults' ability to remember and willingness to recount their own past emotional problems.

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"Like flu, if you follow a cohort of people born in the same year, as they age almost all of them will sooner or later have a serious bout of depression, anxiety or a substance abuse problem" Moffitt says.

It comes as no surprise that, compared with one-time survey responses, the new prospective study identified considerably more people who have had mental disorders, comments epidemiologist Ronald Kessler of Harvard Medical School. But self-report responses remain valuable, he says. Evidence indicates that individuals who report past mental disorders in surveys display an increased likelihood of developing such ailments in the future. Kessler directs ongoing U.S. surveys of mental disorders based on self-reports.

In the new study, half of the people diagnosed (using structured interviews and information from parents and teachers) had a mental disorder for a relatively short period or in a single episode. Moffitt nonetheless regards these cases as serious, since short-term symptoms often led to work problems, efforts to get mental-health care or suicide attempts.

Among 32-year-old New Zealanders, Moffitt and her colleagues find lifetime prevalence rates of 50 percent for anxiety disorders, 41 percent for depression, 32 percent for alcohol dependence and 18 percent for marijuana dependence. Participants who developed one of these disorders tended to experience others as well, including less common ones such as eating disorders.

Self-report surveys in the United States (SN: 6/11/05, p. 372) and New Zealand have found lifetime prevalence rates for common mental disorders that are about half as large as those in the new investigation.

A long-term study of 1,500 North Carolina children tracked into young adulthood finds rates of mental disorders comparable to those reported by Moffitt's team, according to Duke psychologist and study director Jane Costello. Those data have yet to be published.

Researchers generally agree that self-reports underestimate lifetime prevalence rates of mental ailments. Other investigations suggest that many adults forget periods of depression, and even hospitalizations for depression, from earlier in their lives.

Still, some researchers have charged that self-report surveys inflate prevalence rates by assigning mental ailments to many people with mild symptoms of no real clinical concern.

As work intensifies to develop a new version of the diagnostic manual of mental disorders by 2012, Moffitt says the findings indicate that prevalence estimates for serious mental disorders have been too low, not too high. The upcoming manual, known as DSM-V and published by the American Psychiatric Association, will be used as the standard for classifying disorders and for insurance purposes in the United States.

Higher prevalence rates can be used to support either side of along-running dispute over psychiatric diagnoses, Moffitt notes. Some researchers see a large, unmet need for mental-health care, leading them to support definitions of certain mental disorders as serious even if they are not long-lasting. Others want to narrow DSM definitions in order to avoid labeling temporary emotional woes as mental illnesses.

Jerome Wakefield, a professor of social work at New York University, calls the new report "a watershed and a fundamental challenge to the mental-health field and to DSM, just as it is in a process of revision."

In Wakefield's view, current DSM definitions encompass much "normal, often transient, human suffering," which in turn got pegged as mental disorders in Moffitt's study. Researchers have yet to establish how often temporary distress elicited by life's misfortunes gets misclassified as depression, he asserts.

Efforts underway to expand DSM-V's definition of depression "come close to pathologizing the entire population and opening the way for increases in medicating our society" Wakefield says.

Harvard's Kessler disagrees. Mental disorders, like physical ailments, range from mild to severe, he says. Accumulating national survey data indicate that "common cold equivalents" in the mental realm, such as relatively mild or brief episodes of depression and specific phobias, often precede more serious or chronic mental disorders later in life, Kessler remarks.

"It's not surprising either that 99.9 percent of the population has some sort of physical illness at some time in their lives or that the majority of people meet criteria for a mental illness at some time in their lives" Kessler says. Alarm over high lifetime prevalence rates for mental disorders largely reflects stigma attached to these conditions, in his view.

Kessler recommends that DSM-V, unlike its current version, distinguish between mild, moderate and severe forms of major depression.

Moffitt notes that treatment costs and insurance coverage also drive this debate: "How many psychiatric patients are there? Well, there are as many as America can afford to treat."

Back Story | HISTORY OF U.S. PSYCHIATRIC DIAGNOSIS

The Diagnostic and Statistical Manual of Mental Disorders has faced criticism, praise and a series of revisions since it was first published.

1952: DSM-I

The American Psychiatric Association released DSM-I, taking a descriptive, psychoanalytic approach to a relatively small number of mental disorders. This version of the manual had 145 pages.

1968: DSM-II

The review committee tried to improve the uniformity of psychiatric diagnoses. Also, homosexuality was removed from the list in the seventh printing of this version after a vote in 1973. "Sexual orientation disturbance," now "gender identity disorder," was added.

1980: DSM-III

DSM-III defines a larger array of mental disorders--including post-traumatic stress disorder and attention deficit disorder (with or without hyperactivity)--on the basis of lists of symptoms and features associated with the conditions.

1994: DSM-IV

A fourth manual, with more than 880 pages, came after reviews of published literature, reanalyses of data sets and field trials. It includes symptoms' impact on a person's daily life among the diagnostic criteria for many disorders. A text revision was released in 2000.

2012: DSM-V

The next DSM is in its planning and preparation phase and is expected to be released in May 2012. The process has already generated some controversy and public protest, including against the listing of "gender identity disorder."

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