Heart disease, diabetes, depression. It’s the recipe for a lethal cocktail, according to new research findings.

The presence of all three diseases can boost a patient’s death by 20% to 30%, says researcher Anastasia Georgiades, of Duke University in Durham, N.C. 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. There was a higher risk of dying among patients with moderate-to-severe symptoms of depression who were also diabetics, compared with patients with either depression alone or diabetes alone.

The reason for the increased risk is unclear, “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,” Georgiades said.