The findings are published online in the Journal of Affective Disorders.

Up to 4 percent of Americans have some form of bipolar illness, and of those, just under 10 percent also have binge eating disorder -- a higher rate of binge eating than seen in the general population, says co-author Mark Frye, M.D., a psychiatrist and chair of the Department of Psychiatry/Psychology at Mayo Clinic in Rochester. The Diagnostic and Statistical Manual of Mental Disorders (DSM-5) update released this spring recognizes binge eating disorder as a distinct condition, he noted.

Bipolar patients who binge eat are more likely to have other mental health issues such as suicidal thoughts, psychosis, anxiety disorders and substance abuse, the study found. People with bipolar disorder who are obese but do not binge eat are more likely to have serious physical problems such as arthritis, diabetes, high blood pressure and heart disease.

It was more common for women than men with bipolar disorder to binge eat or to be obese, the study showed.

"The illness is more complicated, and then by definition how you would conceptualize how best to individualize treatment is more complicated," Dr. Frye says. "It really underscores the importance of trying to stabilize mood, because we know when people are symptomatic of their bipolar illness their binge frequency is likely to increase. We want to work with treatments that can be helpful but not have weight gain as a significant side effect."

The researchers used the Mayo Clinic Bipolar Biobank, a collaborative effort by Mayo Clinic, the Lindner Center of HOPE, University of Minnesota and Mayo Clinic Health System. More research is planned to see whether there is a genetic link to binge eating disorder in bipolar disease.

"Patients with bipolar disorder and binge eating disorder appear to represent a more severely ill population of bipolar patients. Identification of this subgroup of patients will help determine the underlying causes of bipolar disorder and lead to more effective and personalized treatments," says co-author Susan McElroy, M.D., chief research officer at the Lindner Center of HOPE.

The study was funded by the Marriott family. Co-authors also include Scott Crow, M.D., University of Minnesota Medical School; Nicole Mori of the Lindner Center of HOPE; and Joanna Biernacka, Ph.D., Stacey Winham, Ph.D., Jennifer Geske, Alfredo Cuellar Barboza, M.D., Mikel Prieto, M.D., Mohit Chauhan, M.D., and Lisa Seymour of Mayo Clinic.