The Journals of Gerontology Series A: Biological Sciences and Medical Sciences Advance Access originally published online on February 19, 2009
The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 2009 64A(5):581-589; doi:10.1093/gerona/glp005
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Association Between Inflammatory Components and Physical Function in the Health, Aging, and Body Composition Study: A Principal Component Analysis Approach
1 Department of Biostatistical Sciences
2 Sticht Center on Aging
3 Department of Internal Medicine
4 Department of Epidemiology and Prevention, Wake Forest University School of Medicine, Winston-Salem, North Carolina
5 Division of General Internal Medicine, University of California, San Francisco
6 Division of Geriatric Medicine, University of Pittsburgh, Pennsylvania
7 Department of Epidemiology, Tulane School of Public Health and Tropical Medicine, New Orleans, Louisiana
8 Institute of Health Sciences, VU University Medical Center, Amsterdam, the Netherlands
9 Department of Aging and Geriatric Research, University of Florida, Gainesville
10 Geriatric Epidemiology Section, National Institute on Aging, Bethesda, Maryland
Address for correspondence to Fang-Chi Hsu, PhD, Department of Biostatistical Sciences, Wake Forest University School of Medicine, 100 North Main Street, Suite 2323, Winston-Salem, NC 27101. Email: fhsu{at}wfubmc.edu
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Abstract |
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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-
], sTNFRI, sTNFRII, interleukin [IL]-6sR, IL-2sR) loaded highest on the first component (TNF- 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--related component, but not to the CRP-related component (knee strength: 
= –2.71, p = .002; 
= –0.88, p = .325; physical performance battery score: = –0.05, p < .001; = –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 inflammatory components can be identified in an older population, and these components have inconsistent associations with different aspects of physical performance.
Keywords Inflammation; Physical function; Aging; Principal component analysis
Received: June 18, 2008; Accepted: December 7, 2008