Researchers have long observed that men and women tend to experience mental illnesses at different rates, with women showing higher rates of mood and anxiety disorders, and men showing higher rates of antisocial personality disorder and substance abuse. A new study, published online in September in the Journal of Abnormal Psychology, may have uncovered an underlying reason: A tendency among women to internalize distress (by ruminating on negative thoughts, for instance) and a tendency among men to externalize their distress (through, for example, aggressive or coercive behavior), says the study's lead author Nicholas Eaton, a psychology doctoral candidate at the University of Minnesota.

The researchers analyzed data from a National Institutes of Health survey of 43,093 Americans and looked at which disorders tended to co-occur. They found that, for both men and women, the patterns of co-morbidity looked the same, with depression and anxiety disorders tending to go together, for instance. Overall, the disorders tended to cluster, with externalizing disorders going together and internalizing disorders co-occurring.

The findings show that for men and women, mental illnesses have similar underpinnings, but the sexes differ in how they combine the elements, Eaton says.

"You can think about it like a recipe for making something — say, stew," he says. "Women and men both make stew from the same recipe. However, men might use twice as many ingredients as women, and therefore they'd wind up with twice as much stew at the end."

The findings suggest that prevention efforts might be able to target multiple disorders with a single intervention, for instance by teaching people who tend to internalize how to avoid dwelling on negative thoughts, and by teaching people who tend to externalize distress how to cope with negative emotions in more positive ways, perhaps through exercise or meditation.

—S. Dingfelder