The study was the work of Dr Mary A Whooley, of the VA Medical Center in San Francisco, California, and colleagues from other research centres in the US, Germany and The Netherlands, and was published in the November 26 issue of the Journal of the American Medical Association, JAMA.
Doctors have long known that depression is a risk factor for developing cardiovascular disease in healthy people, and a large body of evidence shows that depression is more common among heart patients and increases the risk of a second cardiovascular event. But the underlying mechanisms have remained somewhat of a mystery.
"Understanding how depression leads to cardiovascular events is necessary for developing interventions to decrease the excess cardiovascular morbidity [illness] and mortality [death] associated with depression," wrote the authors in their background to the article.
For the study, called the Heart and Soul Study, Whooley and colleagues recruited 1,017 patients between September 2000 and December 2002 who were attending 12 outpatient clinics in the San Francisco Bay Area and followed them for an average of 4.8 years up to January 2008. All the participants had stable coronary heart disease.
To enable the researchers to assess symptoms of depression at the start of the study, the patients completed the Patient Health Questionnaire (PHQ). During follow up, the researchers counted incidences of cardiovascular events such as heart failure, myocardial infarction (heart attack), stroke, transient ischemic attack ("mini stroke", a temporary loss of blood flow to the brain), and death. The patients also answered questions about how much physical exercise they had taken in the past month, including sports.
Whooley and colleagues used a range of statistical tools called proportional hazards models to find how any links between symptoms of depression and subsequent cardiovascular events occuring during follow up might be explained by biological or behavioural factors.
The results showed that patients who were depressed at the start of the study had an approximately one third higher risk of another cardiovascular event, which is more or less as expected. But the higher risk vanished when the figures were adjusted to take account of behaviours such as lack of physical activity, not taking medications according to schedule, and smoking.
The results showed that:
- Over 4,876 person-years of follow-up there were 341 cardiovascular events.
- After adjusting for age, the yearly rate of cardiovascular events was 10 per cent among the 199 patients who were depressed (PHQ score equal to or greater than 10) and 6.7 per cent among the 818 patients who were not depressed).
- After adjusting for other illnesses and disease severity, depressive symptoms were linked to a 31 per cent higher rate of cardiovascular events.
- These links were influenced by adjusting for potential biological mediators.
- And after adjusting for potential behavioural mediators (including physical inactivity), the links lost their statistical significance.
"In this sample of outpatients with coronary heart disease, the association between depressive symptoms and adverse cardiovascular events was largely explained by behavioral factors, particularly physical inactivity."
According to Reuters, Whooley said in a telephone interview:
"It's really difficult to tease out where the independent effect of depression is happening and where the other effects of cardiac disease are ending."
"But the message is that once you account for those health behaviors the patients would not longer have this excess risk of cardiac events. The risk would go from one in 10 down to one in 15," she added, explaining that some patients get trapped in a downward spiral of exercising less because they are depressed and this just makes them more depressed.
The authors recommended that heart patients should be offered counselling to help them do more exercise and adopt healthier lifestyles. They wrote that the findings of this study:
"Raise the hypothesis that the increased risk of cardiovascular events associated with depression could potentially be preventable with behavior modification, especially exercise. Given the relatively modest effects of traditional therapies on depressive symptoms in patients with heart disease, there is increasing urgency to identify interventions that not only reduce depressive symptoms but also directly target the mechanisms by which depression leads to cardiovascular events."
"Depressive Symptoms, Health Behaviors, and Risk of Cardiovascular Events in Patients With Coronary Heart Disease."
Mary A. Whooley; Peter de Jonge; Eric Vittinghoff; Christian Otte; Rudolf Moos; Robert M. Carney; Sadia Ali; Sunaina Dowray; Beeya Na; Mitchell D. Feldman; Nelson B. Schiller; Warren S. Browner.
JAMA, Vol. 300 No. 20, pp 2379-2388. November 26, 2008.
Click here for Abstract.
Sources: JAMA, Reuters.
Written by: Catharine Paddock, PhD