About 25 percent of all Americans meet the criteria for a mental disorder, and an estimated half of them have mild cases. But little is known about what turns those mild cases into severe mental health problems over time.

At APA's 2005 Annual Convention, Harvard Medical School epidemiologist Ronald C. Kessler, PhD, called for more research on what factors might exacerbate mild disorders and whether interventions could halt that escalation. He also pressed for more treatment of mild cases.

"There's no other class of conditions in the general population of our country or any other developed country that comes close to having the societal impact of mental disorders," explained Kessler.

Kessler is the principal investigator of the U.S. National Comorbidity Survey (NCS), the nation's first nationally representative survey of mental health disorders, and co-director of the World Health Organization's World Mental Health surveys, a 28-country epidemiological investigation with more than 200,000 respondents. He also directs a U.S. survey of adolescent mental disorder prevalence, the NCS-A. Data from these studies were recently published in the Archives of General Psychiatry (Vol. 62, No. 6, pages 593-602).

Before his talk, he received an APA presidential citation for his scholarly leadership and research in the epidemiology of mental health disorders.

Comorbidity in America

Researchers conducted the first round of NCS from 1990 to 1992 with 8,000 participants and collected follow-up data for the NCS-2 in 2001 and 2002. A 10,000-participant replication survey, the NCS-R, is ongoing.

The surveys have found that about 50 percent of Americans will have a mental health problem at some point in their lives, and a substantial number of individuals are not in treatment. Moreover, a substantial portion of those mental health problems are mild.

"The DSM is a very broad system," he explained. "It's not terribly surprising that half of the population at some time in their life meets criteria for one of those conditions."

Though some have questioned whether such mild conditions should be classified as disorders, Kessler maintained that they should in fact be diagnosed and even treated.

NCS data show that people who had a mild disorder at baseline were two to three times more likely than those with no disorder to have poor outcomes, such as hospitalization or a serious mental illness, 10 years later.

Moreover, those with mild disorders at baseline made up a substantial percentage of those who had severe mental health problems at the 10-year mark. In fact, while the largest proportion of those with severe problems at 10 years had severe problems at baseline, the next largest group consisted of those with mild disorders at baseline. Kessler noted that most of the cases that progress to severe problems involve young adults.

"On the basis of that, we can say that it is probably clinically significant to have something that's mild," said Kessler. "But very few of those mild cases are in treatment."

In fact, he noted that NCS data show it takes an average of nine years for those with depression to enter treatment after the disorder fully manifests; other disorders such as generalized anxiety, phobias and obsessive-compulsive have similar lag times.

Is intervention the answer?

Once people finally do seek help, their problems are severe, noted Kessler. For example, he said, a typical NCS case might involve a young woman who began having social anxiety and school phobia as a girl, then became depressed and started drinking as a teenager, then drops out of high school, has two children and is an alcoholic before seeking treatment.

Intervening with the girl's social anxiety as a child or at the initial onset of depression as a teen might have prevented the challenges she now faces, Kessler said. However, there's no epidemiological evidence that intervention in mild cases could change the course of people's lives, said Kessler.

"The reason is we have very little experience in treating mild cases," he explained, "because we don't see mild cases. The 15-year-olds we see are the ones who are suicidal or have ADHD or oppositional defiant disorder."

That's why, he said, it's important to step up treatment and diagnosis of mild cases--rather than categorize them as nondisordered.

In fact, that's the trend in medicine, he noted, for health problems such as high cholesterol. Originally, about 2.5 percent of the population--those with cholesterol above 250--were considered at high risk, but that cutoff number has steadily been lowered. Kessler noted that studies published last year found it was cost-effective to treat those with cholesterol above 200, about 30 percent of people. Similarly, broadening the treatment of mental health disorders may prove effective, he said.

"We really need better work than we have so far in doing serious large-scale, long-term controlled studies that are naturalistic," he said, "to demonstrate the effectiveness of the kind of work that's done and the implications for people's lives."

Some of the NCS studies help to bridge that gap, analyzing the societal cost of mild mental health problems. For example, the data show that untreated mental disorders are by far the most costly class of health problems, and that, for specific conditions, depression ranks third in cost behind muscular/skeletal problems and sleep/energy problems.

"That's not something that's widely known," he said, noting that psychologists and other mental health providers need to further educate policy-makers to gain additional support for their services and research.

Further Reading

For more on the NCS, see "Study indicates mental illness toll on youth, delays in treatment," in the September Monitor.