When two conditions show up together time after time it grabs the attention of medical and scientific researchers. Such is the case with symptoms of depression and instances of heart disease or stroke, and previous studies have been inconclusive as to which condition was causal for the other. A recent study, however, has been able to demonstrate when depression was a causal factor for the heart problem and when the heart problem caused the depression.
The study, led by Dr. Eric Brunner of University College London (UCL), tracked 10,036 individuals for nearly a quarter century. All of the study participants were 35-55 years old at their initial interview. Researchers used a general health survey along with a recognized depression scale in order to assess each subject for symptoms of depression, and then interviewed the subjects at five and 10 year intervals for the subsequent 24 years, monitoring each subject’s heart health. Medical records were also used to compare heart-related health status to depression symptoms.
The information gathered at the five year assessments indicated that depression was a risk factor for stroke, but subsequent assessments did not reveal a causal relationship. On the other hand, subjects who had undergone a stroke experienced double the occurrences of depression symptoms compared to study subjects who had not had a stroke.
Conversely, investigators discovered that persons with more symptoms of depression did face a heightened risk for heart disease and heart attack. Furthermore, the more severe a person’s depression symptoms the greater their risk for heart disease. This kind of relationship is referred to as a dose response – more symptoms on one side of the relationship equals more risk on the other side of the relationship.
However, after the five year mark there was no clear increased risk for stroke linked to depressive symptoms. The fact that depression is associated with stroke but that symptoms do not predict it suggests that stroke is a causal factor for depression, rather than the reverse.
Heart disease and stroke are among the most common reasons for poor health and disability in the general population. The UCL study demonstrates the intimate connection between mental and physical health. Depression is a serious condition in itself, but this and other studies reveal how it also serves as a risk factor for other illnesses.