Sickness behavior in community-dwelling elderly: associations with impaired cardiac function and inflammation

Sickness behavior is a cluster of symptoms that occur as a response to an infection and alterations in the inflammatory response. Under normal circumstances, sickness behavior is fully reversible once the pathogen has been cleared. Aging and chronic illness such as heart failure are associated with enhanced inflammatory activity that lasts for a long duration and no longer represents an adaptive response. The aim of this study was to explore whether inflammation mediates the relationship between impaired cardiac function and a symptom cluster including anhedonia, fatigue, and sleepiness, which might represent sickness behavior in community-dwelling elders. Structural equation modeling (SEM) showed that the factor impaired cardiac function (i.e., N-terminal fragment of pro-brain natriuretic peptide, left ventricular ejection fraction, and the heart failure medications angiotensin converting enzyme inhibitor, angiotensin receptor blockade, β-blocker, and diuretics) was associated with both inflammation (i.e., C-reactive protein; β = .26) and the symptom cluster (β = .31). Inflammation had a significant direct, but smaller, association with the symptom cluster (β = .21). By this pathway, inflammation also mediated an indirect association between impaired cardiac function and the symptom cluster (β = .05). Including creatinine, blood glucose, ischemic heart disease, previous and current tumor, respiratory disease, age, and body mass index in the SEM model did not change these associations. Our results imply that some aspects of the symptom panorama in elderly individuals with impaired cardiac function or heart failure could represent sickness behavior.