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March 19, 1999
By Mark Moran
"An ounce of prevention. . ." goes the saying, reflecting an age-old medical truth that is finally becoming meaningful in the psychiatric field.
For a host of conditions, from AIDS to coronary artery disease, science has discerned any number of factors-such as genetic, biological, behavioral, and environmental-that can protect an individual from disease or lead to it. This information has been complemented by data from epidemiologic studies of populations over time corroborating links between risk factors and disease. Often elaborate strategies have been put in place to educate the general public about these risks and to target at-risk individuals with preventive interventions.
Yet mental illness has so far seemed to defy similar efforts. Teasing out the genetic, biological, behavioral, and environmental risk factors that may interact over a lengthy developmental course, often beginning in childhood, has proven to be a methodological Mount Everest-to say nothing of the time and expense required to conduct long-term intervention trials for testing prevention strategies.
But today there is a growing body of research on risk and protective factors associated with mental illnesses, and a cadre of prevention scientists are calling for a renewed focus on prevention of mental disorders.
"If we consider what we now know about early risk and moderating factors and about developmental trajectories and variation, we know a great deal compared with what we know about the developmental course for cancer, heart, lung, and blood disease," said psychiatrist Sheppard Kellam, M.D., director of the prevention research department at Johns Hopkins University School of Medicine.
"We know that certain risk factors and family processes in combination with certain biological and environmental interactions are very important predictors, and there is no reason for us to be reluctant to advance the priority of prevention."
Kellam cited studies at Hopkins showing the effect of early classroom environment on development of later conduct disorder. "It turns out that kids who were aggressive and disruptive in first grade and who were also in a [classroom characterized by high aggression and disruption] had a risk for severe aggressive, disruptive behavior in middle school up to as high as 60 times that of the average child," he said. In contrast, "the same child with the same aggressive, disruptive behavior but in a low aggressive, disruptive classroom-in other words, a well-managed class-shows a risk of maybe two and a half to three times the risk for later conduct disorder."
Kellam believes that a preventive approach to mental illness allows researchers and clinicians to think about disorders as occurring across a continuum-from asymptomatic, to presymptomatic, to symptomatic-and within populations, rather than as acute episodes striking individuals.
"What shifts is the developmental stage of the disorder and the denominator," said Kellam of this preventive approach. "We now think of baseline only as a point in time on a developmental trajectory or growth curve. Prevention science as it has matured is much more involved with longitudinal analysis and growth-curve modeling."
The National Advisory Mental Health Council Workgroup Report on Mental Disorders Prevention Research, delivered last year to Steven Hyman, M.D., director of the National Institute of Mental Health (NIMH), cited progress in mental illness prevention research, especially in the area of conduct disorders. The report noted that long-term evaluations of experimental trials of home-visitation programs with high-risk mothers and infants have proven effective in reducing antisocial behavior problems. One 15-year follow-up of a randomized trial of a home-visitation program found that the high-risk mothers in the program had significantly fewer verified reports of child abuse and neglect, fewer arrests for criminal behavior, less impaired behavior from alcohol or drug abuse, and fewer subsequent pregnancies-all of which are risk factors for children's development of conduct disorders.
"Prevention of mental illness is just now catching up with the success of prevention in other fields," said Thomas Coates, Ph.D., a professor of medicine and epidemiology at the University of California, San Francisco, and chair of the work group. "It has taken a while to understand how to do risk-factor research and to develop the methodologies to do the preventive interventions. But if one thinks of cardiovascular disease, it took a long time to figure out the associations with smoking and hypertension and hypercholesterolemia."
Yet last year's report was also largely a catalog of gaps in pre-intervention, intervention, and preventive services research. The gaps are not surprising, however, given the daunting task of doing mental illness prevention research: to identify risk and protective factors for a condition and follow a large at-risk population over time to see whether the condition develops while controlling for confounding variables. Similarly, the job of testing an intervention requires rigorous study design, time, and money.
"You don't want to go forward with an intervention trial-which typically means selecting a group at risk for the disorder and following them for enough time to be sure you are getting an effect-until you have a really good sense of what the risk factors are and a tight trial design so you can really see the effect," said Coates. "It's very different from taking people who are at a symptomatic stage of disease and treating them when you can have smaller sample sizes and a more immediate effect. Mental illness prevention research requires a large sample size and long-term research. And it's expensive."
In contrast to the optimism expressed by some prevention researchers, Hyman believes the ability to use population-based strategies for prevention of common mental disorders is a dream still to be deferred. But he says that while the traditional public health model of prevention may not yet be attainable, the tools of prevention can be applied over the life course of a mental disorder to avoid disability and relapse.
"We really don't know how to prevent depression or anxiety disorders or schizophrenia," he told Psychiatric News. "But what we do recognize is that these are chronic life-course disorders. As in the case of all chronic disease, what we want to think about is preventing progression of symptoms to full-blown illness and prevention of disability."
In keeping with recommendations from last year's report on mental disorders prevention research, Hyman has vowed to expand NIMH's epidemiology portfolio to provide better data on prevalence and incidence of mental illness. These, in turn, can be used to follow populations over time and work toward development of risk profiles.
In the meantime, Hyman is critical of prevention theories that he believes have not been tested in the crucible of real-world intervention trials-especially those that draw on the resources of schools and other societal institutions. "We care a great deal that we do things that will be relevant to the real world, and when you recognize what schools are being asked to do other than simply teach, we have to be sure that these things are appropriately targeted and have an appropriate impact," said Hyman. "What I am looking for is research that is going to have an impact in the real world."
He cites depression in children as an example of how better epidemiologic data and a preventive approach can be applied to averting disability and relapse, even if the field is not yet able to prevent the onset of symptoms.
"There are data that perhaps only 20 percent of children taken to primary care providers with depression get appropriate treatment," he said. "We should remember that depression is a continuous variable, like blood pressure. The DSM gives us an arbitrary cutoff in terms of severity and time, but what we need to know are the children's attributes, risks, and actual symptoms that would help us intervene, most likely with psychotherapy, to prevent full-blown depression."
Until the public health model of prevention becomes a reality, the concept of mental illness as a life course disorder should be critical for office-based clinicians.
"The best clinicians conceptualize mental illness as recurring across a life span and are always thinking not only about the acute treatment episode, but about the long-term course, including the prevention of relapse and disability," he said.