The phrase “mind-body connection” is so overused it sounds like a cliché, yet there’s a significant body of research that shows mental and physical health are in fact deeply intertwined. Despite that, healthcare systems are still slow to integrate mental and physical healthcare in order to provide better patient care. To address this, Swiss psychologists set out to study instances in which specific mental health disorders are followed or accompanied by physical disorders in adolescents. The goal was to determine a causal relationship between them, and if possible, to predict certain physical illnesses by the presence of a mental disorder.

What they found were small—but definite—associations between certain mental and physical disorders. In their paper, published in PLOS One, the authors write, “The most substantial associations with physical diseases preceding mental disorders included those between heart diseases and anxiety disorders, epilepsy and eating disorders, and heart diseases and any mental disorder.”

“To have proof of causality, you have to experimentally manipulate people being physically or mentally sick, which isn’t ethical,” Gunther Meinlschmidt, co-lead author of the study and a professor of psychology at University of Basel, Switzerland tells mental_floss. Since that wasn’t possible, he and the research team, led by Marion Tegethoff, analyzed data from a large co-morbidity survey of 6483 U.S. teenagers, aged 13 to 18.

Using statistical models, they first looked at whether mental disorders predicted physical disease. Indeed, arthritis and digestive disorders were more common after depression in adolescents, while skin disorders seem to follow anxiety disorders. Next, they reversed the variables, to see if physical disease was a better predictor of mental disorders. But those results were statistically very small, suggesting that the physical disorders either follow the mental disorders, or arise at the same time.

More research with larger sample sizes still needs to be done, including recruiting subjects who have both a physical and mental condition. Meinlschmidt plans to “try to understand if someone was treated, say, for epilepsy—does it effect [their] eating disorder?” This will help the team isolate strict causality, he says. However, “With this work, we go beyond mere associations toward these temporal or chronological associations. One indicator increases the confidence that something causal might be going on.”

This research is a necessary first step that “stresses the importance of integrative health care to have close collaboration with a system for treating people with mental disorders and physical illness,” Meinlschmidt says. Up to now, these “two separate worlds are not really working closely together.” His ultimate goal is “to dig deeper into potential mechanisms for developing new interventions." He hopes his research will bring more integration to two systems and help doctors create more integrated ways of treating a person’s health.