Having depression or heart disease is bad enough, but having a combination of the two can be significantly more lethal than either one of them on their own, researchers wrote in an article published in the medical journal Heart. According to previous research, people who were diagnosed with depression but were otherwise healthy had a higher risk of developing coronary heart disease, regardless of what other risk factors they had.

There is a higher risk of death from all causes among people with depression, the authors inform. However, before this study nobody was sure whether depression was more fatal for those with or without heart disease.

The researchers gathered data on nearly 6,000 adults in the British Whitehall II study, whose physical and mental health were followed up for five and a half years. The Whitehall II Study examined social and economic factors on the long-term health of approximately 10,000 civil servants aged 35-55 in 1985.

Approximately 14.9% of them scored highly on a depressive symptom scale. 20% of those diagnosed with heart disease were depressed, compared to just 14% of those with no heart problems.

170 civil servants died during the 5.5 year monitoring period. 47 of those deaths were due to heart attack or stroke.

The authors wrote that: The individuals with coronary heart disease alone had a 67% higher risk of dying of all causes compared to others. Those with depression who were otherwise healthy were twice as likely to die from all causes compared to people who had neither depression nor heart disease. Individuals who had a combination of depression and heart disease were nearly five times as likely to die from all causes compared to others with neither depression nor heart disease When relevant influential factors were taken into account, such as age and sex, the investigators found that those with a combination of heart disease and depression had three times the risk of death from all causes, and four times the risk of death from heart attack or stroke, compared to healthy individuals.

The authors say that nobody is sure why depression has an impact on risk of death. They suggest it may involve a stimulation of the inflammatory process, clot formation, a change in cellular responses, an alteration in the metabolism of blood lipids (fats), as well as some behavioral factors.

They concluded:

This study provides evidence that depressive symptoms are associated with an increased risk of all-cause and cardiovascular death and that this risk is particularly marked in depressive participants with co-morbid CHD.

They added that there is a need for healthcare professionals to focus on possible depressive symptoms in cardiac patients.

Effects of depressive symptoms and coronary heart disease and their interactive associations on mortality in middle-aged adults: the Whitehall II cohort study
Hermann Nabi, Martin J Shipley, Jussi Vahtera, Martica Hall, Jyrki Korkeila, Michael G Marmot, Mika Kivimäki, Archana Singh-Manoux
Heart doi:10.1136/hrt.2010.198507