Elevated IL-6 and CRP Levels Are Associated With Incident Self-Reported Major Mobility Disability: A Pooled Analysis of Older Adults With Slow Gait Speed
Daniel P. Beavers, Stephen B. Kritchevsky, Thomas M. Gill, Walter T. Ambrosius, Stephen D. Anton, Roger A. Fielding, Abby C. King, W. Jack Rejeski, Laura Lovato, Mary Mcdermott, Anne B. Newman, Marco Pahor, Michael P. Walkup, Russell P. Tracy, Todd M. Manini
Abstract
BACKGROUND: Elevated interleukine-6 (IL-6) and C-reactive protein (CRP) are associated with aging-related reductions in physical function, but little is known about their independent and combined relationships with major mobility disability (MMD), defined as the self-reported inability to walk a quarter mile. METHODS: We estimated the absolute and relative effect of elevated baseline IL-6, CRP, and their combination on self-reported MMD risk among older adults (≥68 years; 59% female) with slow gait speed (<1.0 m/s). Participants were MMD-free at baseline. IL-6 and CRP were assessed using a central laboratory. The study combined a cohort of community-dwelling high-functioning older adults (Health ABC) with 2 trials of low-functioning adults at risk of MMD (LIFE-P, LIFE). Analyses utilized Poisson regression for absolute MMD incidence and proportional hazards models for relative risk. RESULTS: We found higher MMD risk per unit increase in log IL-6 (hazard ratio [HR] = 1.26; 95% confidence interval [95% CI] 1.13-1.41). IL-6 meeting predetermined threshold considered to be high (>2.5 pg/mL) was similarly associated with higher risk of MMD (HR = 1.31; 95% CI 1.12-1.54). Elevated CRP (CRP >3.0 mg/L) was also associated with increased MMD risk (HR = 1.38; 95% CI 1.10-1.74). The CRP effect was more pronounced among participants with elevated IL-6 (HR = 1.62; 95% CI 1.12-2.33) compared to lower IL-6 levels (HR = 1.19; 95% CI 0.85-1.66). CONCLUSIONS: High baseline IL-6 and CRP were associated with an increased risk of MMD among older adults with slow gait speed. A combined biomarker model suggests CRP was associated with MMD when IL-6 was elevated.