Symptoms of depression may be causally linked to the risk of coronary heart disease. This is according to new research recently published in the European Journal of Preventive Cardiology.
The research team, including Dr. Eric Brunner of the Department of Epidemiology and Public Health at University College London in the UK, says the findings indicate that depressive symptoms should be considered potential risk factors for coronary heart disease (CHD).
The investigators say previous research that has assessed the link between depression and cardiovascular disease is diverse, in that some studies have shown strong associations between the two while others have been inconclusive.
The team notes that some studies in dispute of the association may be biased as a result of "reverse causation." This means that vascular disease has not been deemed as the consequence of depressive symptoms, but as the influence.
Furthermore, the investigators question the accuracy of depressive symptoms assessed in previous research.
For their study, the researchers decided to exclude reverse causation as an explanation for the association between depression and vascular events.
They also set out to determine whether there is any evidence that the likelihood or severity of depressive symptoms are a direct cause of vascular events. This is known as a "dose-response" effect.
The investigators analyzed data of 10,308 civil servants in the UK who were a part of the Whitehall II study.
All participants underwent clinical examination and were required to complete a 30-item General Health Questionnaire.
Subjects were followed up for 20 years. During this time, health assessments were carried out every 2-3 years and any major stroke or CHD events were recorded. Participants were also measured for their "exposure" to depression on six separate occasions.
'No causal relationship between depression and stroke'
From their analysis, the researchers found that participants who showed depressive symptoms in the first one or two assessments demonstrated no increased risk of CHD. But those who had symptoms of depression in the third or fourth assessments showed a 100% increase in risk of CHD.
However, the researchers found that the link between depressive symptoms and stroke only appeared after a short follow-up period. This suggests that the link between depression and stroke is a reverse causation effect.
"In other words, depressive symptoms may be a sign of imminent stroke, but are not causally related," says Dr. Brunner.
Furthermore, the investigators say they found no evidence of a dose-response effect with stroke, indicating that depressive symptoms are not a cause of vascular disease when it comes to stroke, but they are a consequence.
From this, the researchers say their findings provide "evidence supporting a causal relationship between depression and CHD, in contrast to the findings in relation to stroke."
Commenting on the findings, Dr. Brunner says:
"European prevention guidelines refer to depression as a coronary risk factor, and in our study repeated episodes of depressive symptoms accounted for 10% of all CHD events in the study population.
However, this figure relies on the strong assumption of a direct causal mechanism. Whether or not the association is causal, supporting individuals to recover from chronic or repeated episodes of depression has merit, particularly if the individual is then better able to reduce any vascular risk, for example by quitting smoking."
Last year, Medical News Today reported on a study suggesting that depression is the second leading cause of disability worldwide.