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Research suggests link between inflammation, depression and pathogen host defense

Analysis of three cross-sectional surveys showed an association between inflammation and depression symptoms, particularly sleep problems, tiredness, lack of energy and appetite changes, providing further evidence for the evolutionary view that inflammation and depression are associated with pathogen host defense.

“Elevated levels of inflammatory markers, such as C-reactive protein, are well-documented in people with depression,” Markus Jokela, PhD, of University of Helsinki, Finland, and colleagues wrote. “Higher levels of inflammation are particularly likely to underlie depression symptoms that characterize sickness behavior, including fatigue, reduced appetite, withdrawal and inhibited motivation. From an evolutionary perspective, such symptoms have the beneficial effect of preserving energy resources for use in fighting infection and promoting healing processes.”

To evaluate if the association between C-reactive protein and depression is symptom-specific, researchers analyzed data from the U.S. National Health and Nutrition Surveys for 2005 to 2006 (n = 4,593), 2007 to 2008 (n = 5,151) and 2009 to 2010 (n = 5,327). Overall, 15,071 participants (mean age, 47.5 years) were included in the current analysis. C-reactive protein was measured via standard procedures and depressive symptoms were assessed via the Depression Screener Questionnaire as part of computer-assisted personal interviews.

C-reactive protein was associated with all specific depression symptoms when not adjusting for other depression symptoms.

When adjusting for other depression symptoms, C-reactive protein was independently associated with sleep problems (OR = 1.14; 95% CI, 1.07-1.21), tiredness or lack of energy (OR = 1.22; 95% CI, 1.15-1.3) and changes in appetite (OR = 1.17; 95% CI, 1.09-1.27).

The independent association between C-reactive protein and anhedonia almost reached statistical significance (P = .06), according to researchers.

When C-reactive protein was categorized into quartiles, researchers observed independent dose-response patterns for sleeping problems (P < .001), tiredness or lack of energy (P < .001), and changes in appetite (P < .001).

“This pattern of results is consistent with the evolutionary view linking inflammation and depression with pathogen host defense because tiredness, lack of energy and reduced appetite are primary characteristics of sickness behavior. Further research is needed to determine whether changes in inflammation predict changes in specific symptoms and to identify metabolic pathways that mediate such changes,” the researchers concluded. – by Amanda Oldt

Disclosure: The researchers report no relevant financial disclosures.