Scientists have known that heart patients who also suffer from depression are at greater risk for a subsequent attack. But the experts did not quite know why. Epidemiologists at Ohio State University’s School of Public Health have offered an intriguing explanation. They scanned the blood of depressed and nondepressed heart patients and found that those with deflated moods are pumping out twice the level of a pro-inflammatory molecule that can damage vascular muscle.

The scientists asked 32 patients who were under care for heart failure to fill out a questionnaire that identifies depression. For patients who ranked high on that scale, one immune system messenger molecule called tumor necrosis factor alpha was almost twice as high in the bloodstream than it was for the other survey respondents. “This suggests a mechanism linking depression to heart failure,” says Amy K. Ferketich, an assistant professor of epidemiology at Ohio State University and head of the investigation. She suspects that identifying and treating depression in patients with cardiovascular disease could offer greater prevention against recurring vascular problems.