Mood disorders and cardiovascular disease (CVD) are often linked—1 mechanism may be common underlying low-grade inflammation. Specifically, studies have found a consistent association between circulating levels of pro-inflammatory cytokines with both mood disorders and CVD, say researchers from Lausanne University Hospital and Bern University Hospital, in Switzerland and National Institute of Mental Health in Maryland. They suggest that influence may be oneway: Mood disorders may lead to inflammation, but inflammation may not be a risk factor for the onset of mood disorders.
Noting that much of the research on inflammatory markers and CVD has focused on dysthymia, the researchers decided to conduct a study to investigate any association between atypical subtype of dysthymia and increased levels of inflammatory markers. They analyzed data from 3,118 participants who underwent comprehensive somatic and psychiatric evaluations at baseline and a mean of 5.5 years later. Current and remitted mood disorders included bipolar and major depressive disorders (MDD); subtypes included atypical, melancholic, and combinations of those.
After adjusting for confounders, they found current combined MDD was associated with increased high sensitivity C-reactive protein (hsCRP) levels and decreased IL-6 levels. Current atypical MDD was associated with increased hsCRP levels at follow-up. Moreover, remitted melancholic MDD was associated with decreased IL-6 levels at follow-up.
The major finding, the researchers say, was the association between the current atypical subtype of MDD at baseline with increased levels of hsCRP at follow-up. By contrast, inflammatory levels at baseline were not associated with subsequent atypical MDD at follow-up. What this suggests is that the disorder is causally related to increased inflammation, rather than inflammation increasing the mood disorder.
The finding of unidirectional association seems to be specific to the atypical subtype of MDD, the researchers add, which is characterized by somatic symptoms, including sleep, energy, and eating behavior.