People with heart conditions who also experience chronic depression are at greater risk of dying, say researchers, who point out that those with mild or occasional depression didn't face the same threat.

Researchers looked at the association between occasional or persistent mental distress and the risk of death in 950 people with stable coronary heart disease who were between 31 and 74 years old. All participants were part of a study called the Long Term Intervention with Pravastatin in Ischaemic Disease Trial and had had a heart attack or other heart condition up to three years previously.

Each participant answered a stress-test questionnaire at various intervals: at 6 months, one year, two years, and four years. Overall health — as well as survival rates — were then tracked for an average of 12 years.

During that period, 398 people died from all causes and 199 died from cardiovascular disease.

The results were telling: 587 (62 percent) said they had not been distressed at any of the assessments, while around 1 in 4 (27 percent) said they had experienced occasional distress of any severity. Around 1 in 10 (8 percent) said they had experienced persistent mild distress, and 35 people (4 percent) complained of persistent moderate distress.

This last group were nearly four times as likely to have died of heart disease and nearly three times as likely to have died from any cause as those who said they had not been distressed during the intervals.

No such associations were observed for those who said they had only mild anxiety or those who said they had only experienced anxiety occasionally.

Dr. Gjin Ndrepepa of the Technical University in Munich, Germany, wrote that “these findings suggest that in patients with stable [coronary heart disease], long-term mortality risk is related to the cumulative burden of psychological distress,” adding that the study "helps to uncover the intricate relationship between psychological distress and cardiovascular disease.”

The study was published in the Heart journal, an online publication of BMJ.

The researchers stressed some factors to consider: Since this was an observational study, no firm conclusions could be drawn about cause and effect. And the study was limited by the length of time — four years of study period might underestimate the true impact of persistent distress.

Add to that, the researchers stress they didn’t account for the impact of traumatic life events or socioeconomic factors.

But the connection has long been suspected, and at least the implication is clear: Anxiety boosts stress hormones, which can manifest in harmful physiological changes, some of which may be permanent, the researchers report.

The upshot: It's crucial to routinely screen for anxiety and mental distress in patients with heart disease.