The Link Between Mental Illness and Physical Illness

The Link Between Mental Illness and Physical Illness

Why you should care

Mind and body are more deeply intertwined than you might think.

“Heartache.” “A gut feeling.” “Butterflies in your stomach.” Deride them as clichés, but the phrases illustrate a truth: the constant interaction between mind and body. By now plenty of research backs the mind-body connection, but a classic chicken-or-egg question continues to befuddle: Does mental illness cause physical illness, or vice versa?

A recent PLOS ONE study takes a stab at answering that very question. Its conclusion:

It depends on what illness you’re talking about.

Based on data from nearly 6,500 teenagers in the United States, researchers at the University of Basel in Switzerland found distinct patterns in the sequence in which they experienced various ailments: Those who suffered from one had a higher likelihood of developing another. For instance, digestive disorders and arthritis often followed depression and other mood disorders. And teens who had already suffered from heart disease were more likely to develop anxiety disorders later. The findings suggest the medical community should rethink its tendency to treat mental and physical disorders separately, says study investigator Gunther Meinlschmidt.

Studies have already shown that certain mental and physical illnesses tend to occur together, but Meinlschmidt’s team wanted to tease apart the details — namely, whether one precedes another — by examining data from large numbers of people. Consistently seeing one disorder precede another in a large number of people doesn’t prove a causal relationship between them, but it does suggest one. Meinlschmidt and his team also wanted to know whether these associations start early in life, during childhood or adolescence.

Teens who had depression, bipolar disorder and other mood disorders were more likely to suffer from arthritis and digestive disorders later.

So they analyzed data from the National Comorbidity Survey Adolescent Supplement, a survey of 6,438 U.S. teenagers ranging 13-18 years old. The teens completed diagnostic interviews to test for the presence of mental disorders. Their parents or guardians responded to questions about the teens’ mental health, too. The teens also filled out a checklist of physical illness symptoms, and answered questions about diagnoses of physical illnesses they had received from their doctor.

Meinlschmidt’s team ran the data through statistical software to search for trends in the timing of the onset and co-occurrence of various mental and physical illnesses. In some cases, mental disorders predicted physical disease. On average, teens who had depression, bipolar disorder and other mood disorders were more likely to suffer from arthritis and digestive disorders later, and those with anxiety disorders were more likely to develop skin diseases later. Substance abuse tended to precede seasonal allergies. But physical diseases also predicted mental disorders. Having a heart disease was followed by a heightened risk of suffering from anxiety disorders. The researchers saw the same association between epilepsy and eating disorders.

The latter association “was really astonishing,” Meinlschmidt says. Only case studies have reported eating disorders following epilepsy; it’s often thought that eating disorders cause nutrient imbalances that then lead to physical symptoms. Meinlschmidt’s findings add to evidence that the opposite is true, suggesting the potential of anti-epileptic drugs to treat eating disorders. Of course, “this is really speculative,” he notes, but “might be worth looking at further.”

Dr. Emeran Mayer, a professor of medicine at the David Geffen School of Medicine at UCLA and author of the book The Mind-Gut Connection, says the findings are consistent with earlier studies linking certain gastrointestinal and behavioral disorders, as well as studies finding an increased risk of depression after heart attacks and bypass surgery.

To be sure, the study didn’t analyze data tracking the participants over time, which could have provided a more complete picture of the mental-physical health associations, Mayer says, a limitation Meinlschmidt’s team acknowledges in their paper. Still, Mayer believes the large sample size is a major strength of the study and that overall, “it’s an important study.”

The researchers write that their findings support a more integrative approach to medicine. “Mental and physical health care are separate worlds,” Meinlschmidt says. “Either you see a psychologist or psychiatrist, or you see your general physician.” But health care should reflect patients’ experience, he notes. “For people in the real world, they’re not separate.”

If you suspect that any mental and physical illnesses you’ve experienced are related, that might very well be the case. For instance, don’t be surprised if your panic attack-prone child also develops gastrointestinal problems, Mayer says. “It’s not just by chance that [mental and physical illnesses] are co-occurring,” Meinlschmidt says. “There’s a high probability they can trigger each other.”

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