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For Those With One Disorder, What's the Risk of Another?

Research examines how having one mental disorder increases risk for a second.

By Tara Santora

Mental disorders are often interconnected, though previous research has only traced a few strands of the tangled web. But a new study has outlined the complicated paths in unusually comprehensive detail, revealing hidden relationships between the chances of having one mental disorder and developing a second.

Olena Yakobchuk/Shutterstock
Source: Olena Yakobchuk/Shutterstock

For the study, published in JAMA Psychiatry, scientists analyzed the mental health records of nearly six million people in Denmark from periods of up to 17 years. They assessed mental disorders by category—such as personality disorder, eating disorder, or substance use disorder—and found that an initial diagnosis in one category elevated the risk of a second diagnosis in any other category. They also broke down the risk by age, sex, and time since diagnosis to create tailored predictions. Visualizations of the results are available on an interactive website that they created.

“It’s like we developed Google Maps for every type of mental disorder, and we've gone down to the street level,” says senior author and psychiatrist John McGrath, the director of the Queensland Centre for Mental Health Research in Australia.

For example, around 10 percent of people with a mood disorder (such as depression or bipolar disorder) were diagnosed, just one month later, with one of the conditions classified in this study as a “neurotic disorder,” which included anxiety disorders. A more specific example of their findings: A woman diagnosed with a mood disorder before age 20 had a nearly 40 percent chance of developing a neurotic disorder within five years.

Developing a second mental disorder after having one is "the rule, not the exception,” McGrath says. But he doesn’t want to scare people, only to equip them with information so they can better prepare for mental health risks. “We’re not saying you’re doomed to get [a particular condition],” he says.

Doctors might teach people at high risk of developing a specific type of mental disorder how to recognize the warning signs, so patients can seek early treatment if they begin to develop symptoms. Even in the absence of reliable techniques to prevent mental disorders, McGrath says, clinicians can use strategies to help in some cases. Psychologists can, for example, provide cognitive-behavioral therapy and teach relaxation exercises to those at risk for anxiety.

Kids and young adults with a mental disorder appear to be especially at risk of developing another. “If a person has their first mental illness when they’re young, say under 20,” McGrath says, “their risk of going on to get another mental illness is much, much higher than those with a first mental illness at 30 or 50.”

One question the study doesn’t answer is why having one mental disorder amplifies the risk of developing another, says Jordan Smoller, a psychiatrist at Harvard Medical School who was not involved in the study.

While the study can’t answer Smoller’s question, it does hint at possibilities. McGrath’s team found that many mental disorder pairs, such as mood and neurotic disorders, are about equally predictive of each other. A potential explanation for this two-way street is that mental disorders are caused in part by overlapping genetic factors and environmental factors like severe trauma, McGrath says.

He hopes to eventually tease apart which mental disorders should be reclassified or combined into one diagnosis. “The labels we use to describe mental illnesses are interim, temporary placeholders,” McGrath says. “They describe surface-level symptoms, but many of these disorders go together.” His research could help show which disorders are potentially just different expressions of a common underlying issue.

Another drawback of the study, Smoller says, is that researchers compared large groupings of mental disorders (like developmental disorders and behavioral disorders), instead of individuals disorders (like autism spectrum disorder or ADHD). But the research team is currently working to analyze comorbidities at the level of individual mental disorders as well. McGrath also plans to study comorbidities that occur in clusters, not just in groups of two. These next steps could provide more in-depth knowledge about a patient’s risk of developing a second or third mental disorder and ultimately lead to more nuanced prevention and early treatment strategies, he says.

“We do not have good treatments to prevent mental illness,” McGrath says, but identifying whether a person is likely to develop another disorder could help doctors and patients to prepare as much as possible.

Tara Santora is an Editorial Intern at Psychology Today.

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