Heart disease, diabetes and depression can be a lethal triple-play - boosting a patient's death risk by up to 30 percent, new research shows. 

"We do not know what this increased risk is due to, but it could either be that depression influences crucial aspects of self-care behaviors needed to manage diabetes or that a more severe disease process is reflected in more depressive symptoms," said lead researcher Anastasia Georgiades, a research associate in the department of psychiatry and behavioral science at Duke University in Durham, N.C.

In their study, the Duke team followed 933 heart patients for more than four years. During that time, there were 135 deaths among patients with type 2 diabetes and/or depression, the researchers found.

Among patients with moderate-to-severe symptoms of depression who were also diabetics, the researchers observed a significant 30 percent greater risk of dying over the four-year period compared with patients with either depression alone or diabetes alone. These data suggest that diabetes and depression exacerbate each other, but the reasons for this relationship aren't clear.

"Future research will also aim to investigate the mechanisms behind the associations closer. In the meantime, our advice is that physicians monitor these potential high-risk patients carefully," she said.

Co-author Lana Watkins, an assistant research professor, noted that "if you or a loved one has coronary artery disease and diabetes, depression may impact your survival, particularly if it's severe enough to interfere with your daily activities." "This is an interesting study that replicates earlier work showing that symptoms of depression are associated with survival in persons with coronary artery disease," said Robert M. Carney, a professor of psychiatry and director of the Behavioral Medicine Center at Washington University School of Medicine in St. Louis.

Other studies have shown that depression is very common in patients with diabetes, and it is associated with poorer metabolic control and long-term complications in these patients, Carney said.  "The researchers also report a possible interaction between depression and diabetes in patients with coronary artery disease, such that having both disorders may more than additively increase the risk for mortality," the expert noted.

"This is potentially a very important finding, as it suggests a possible link between these two risk factors," Carney said. "This could help to identify those individuals at highest risk for dying and possibly lead to novel treatment strategies to improve survival in these patients."