Patients with heart disease may have a higher mortality rate if they suffer from depression, according to findings published in the journal Heart.

Over the course of five and a half years, a team of researchers observed the mental and physical health of approximately 6,000 people.

During the study, an estimated 15 percent of the individuals were diagnosed with depression, and of this group, 20 percent had developed a form of heart disease. Furthermore, approximately 14 percent of the participants had cardiovascular problems.

At the end of the trial, a total of 170 people had passed away with 63 percent of the group dying from coronary heart disease. Also, suffering from a heart attack or stroke was the cause of death in 47 people.

The researchers discovered that individuals who had been diagnosed with depression and poor cardiovascular health were five times more likely to die compared to participants who were free of both health problems.

While other studies have suggested that depression can cause inflammation and the forming of blood clots, the team concluded that further studies will be needed to determine the biological causes of this mental disorder on heart health.

In 2006, an estimated 81.1 million Americans were diagnosed with at least one type of cardiovascular disease, including approximately 6.4 million suffering from strokes, the American Heart Association reports.