Multimorbidity, inflammation, and disability: a longitudinal mediational analysis

Background: Using longitudinal data from the Survey of Mid-Life Development in the United States, this study examined the role of systemic inflammation in mediating the link between multimorbidity and increases in and onset of functional limitations over a 17-19 year follow-up period. Methods: Participants completed questionnaire assessments of chronic conditions and functional limitations. Interleukin-6, C-reactive protein, and fibrinogen were assayed in serum. Structural equation models were used to predict increases in and onset of functional limitations associated with baseline multimorbidity status; mediation by inflammation was also determined. Results: Multimorbidity (versus 0-1 conditions) predicted more functional limitations and greater odds of onset of limitations over time. Significant indirect effects showed that inflammation partially mediated the link between multimorbidity and changes in, but not onset of, limitations. Discussion: These results show that inflammation, a nonspecific marker of multiple disease conditions, explains in part the degree to which multimorbidity is disabling.