Inflammation has been linked with depression in recent research, but scientists have yet to determine if inflammation in the body is a consequence of, or contributor to, major depression.
A new study suggests that depression is the likely instigator. However, given the episodic pattern of depression, inflammation may persist even when depressive symptoms have subsided.
Inflammation in the body is common to many diseases including infections, malignancy and tissue injuries.
Depression has also been linked to an inflammation marker in blood called C-reactive protein (CRP), a biomarker that is often associated with an increased risk of diabetes, hypertension and cardiovascular disease.
In the study, William Copeland, Ph.D., at Duke University Medical Center and his colleagues tested the direction of association between depression and CRP in a large sample of adolescent and young adult volunteers.
The researchers studied the children as they matured into adulthood. This longitudinal approach allowed the experts to assess changes over time in both CRP levels and any depressive symptoms or episodes.
Investigators found that elevated levels of CRP did not predict later depression, but the number of cumulative depressive episodes was associated with increased levels of CRP.
“Our results support a pathway from childhood depression to increased levels of CRP, even after accounting for other health-related behaviors that are known to influence inflammation. We found no support for the pathway from CRP to increased risk for depression,” said Copeland.
The study is presented in the journal Biological Psychiatry.
Researchers say that the findings suggest that, by this measure (CRP levels), depression is more likely to contribute to inflammation in the body as opposed to arise as a consequence of inflammation in the body.
The highest levels of CRP were found in those who had endured the wear and tear of multiple depressive episodes.
Experts believe this could mean that long-term emotional distress, beginning in childhood, may influence the development of cardiovascular disease and diabetes in middle-age.
“Depression is a recurring disorder for many people. Thus the finding that repeated episodes of depression contribute to inflammation in the body highlights a potentially important role for untreated depression as a contributor to a range of serious medical problems,” commented Dr. John Krystal, Editor of Biological Psychiatry.
“These data add to growing evidence of the medical importance of effectively treating depression.”