According to researchers, the strength of the association of depression with future heart disease is similar to that of traditional risk factors like smoking, high blood pressure and elevated cholesterol.
In a study to examine both directions of the depression-inflammation connection and to measure the physical symptoms of depression, such as fatigue and sleep disturbance, in addition to the cognitive-emotional symptoms, such as pessimism and sadness, it was found that depression leads to elevated inflammatory proteins in the human body.
Symptoms of depression are associated with increases over time in interleukin-6, an inflammatory protein that predicts cardiovascular events. In contrast, levels of interleukin-6 are not related to later increases in depressive symptoms.
Several previous studies have linked depression to increased inflammatory protein levels measured at the same time. These studies, however, cannot speak to which is the cause and which is the effect. “There is two-way communication between the brain and the immune system, so we had to determine whether activation of the body’s immune system sent a signal to the brain to affect mood and behavior or whether the depression activated the immune system,” said study leader Dr. Jesse Stewart.
Participants in the study were 263 healthy men and women aged 50-70 years at the start of the study. They were tested at baseline and again six years later to determine their levels of depressive symptoms and interleukin-6. Levels of C-reactive protein, another inflammatory protein, were also measured but were not related to depression.
“Promotion of inflammation may be one pathway through which depression may negatively influence cardiovascular health. The link to cardiovascular disease demonstrates that there may be physical as well as mental health reasons to treat depression,” said Dr. Stewart.
References:
1. Jesse C. Stewart, Kevin L. Rand, Matthew F. Muldoon, Thomas W. Kamarck. A prospective evaluation of the directionality of the depression-inflammation relationship. Brain, Behavior, and Immunity, Volume 23, Issue 7, October 2009, Pages 936-944.
