Association Between Inflammatory Components and Physical Function in the Health, Aging, and Body Composition Study: A Principal Component Analysis Approach

Background. In older adults, studies demonstrate an inverse relationship between physical function and individual inflammatory biomarkers. Given that the inflammatory response is a complex system, a combination of biomarkers may increase the strength and consistency of these associations. This study uses principal component analysis to identify inflammatory component(s) and evaluates associations between the identified component(s) and measures of physical function. Methods. Principal component analysis with a varimax rotation was used to identify two components from eight inflammatory biomarkers measured in 1,269 older persons. The study sample is a subset of the Health, Aging, and Body Composition study. Results. The two components explained 56% of the total variance in the data (34%, component 1 and 22%, component 2). Five markers (tumor necrosis factor-alpha [TNF-alpha], sTNFRI, sTNFRII, interleukin [IL]-6sR, IL-2sR) loaded highest on the first component (TNF-alpha related), whereas three markers (C-reactive protein [CRP], IL-6, plasminogen activator inhibitor-1) loaded highest on the second component (CRP related). After adjusting for age, sex, race, site, sampling indicator, total lean and fat mass, physical activity, smoking, and anti-inflammatory drug use, knee strength and a physical performance battery score were inversely related to the TNF-alpha-related component, but not to the CRP-related component (knee strength: (beta) over cap (TNF alpha) = -2.71, p = .002; (beta) over cap (CRP) = -0.88, p = .325; physical performance battery score: (beta) over cap (TNF alpha) = -0.05, p < .001; <(beta)over cap>(CRP) = -0.02, p = .171). Both components were positively associated with 400-m walk time, inversely associated with grip strength, and not associated with 20-m walking speed. Conclusions. At least two infl ammatory components can be identifi ed in an older population, and these components have inconsistent associations with different aspects of physical performance.