title: Association between inflammatory components and physical function in the health, aging, and body composition study: a principal component analysis approach.
abstract: 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: betaTNFalpha = -2.71, p = .002; betaCRP = -0.88, p = .325; physical performance battery score: betaTNFalpha = -0.05, p < .001; betaCRP = -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.
authors.affiliation: Department of Biostatistical Sciences, Wake Forest University School of Medicine, 100 North Main Street, Suite 2323, Winston-Salem, NC 27101, USA. fhsu@wfubmc.edu
authors.forename: Fang-Chi
authors.initials: FC
authors.lastname: Hsu
authors.forename: Stephen B
authors.initials: SB
authors.lastname: Kritchevsky
authors.forename: Yongmei
authors.initials: Y
authors.lastname: Liu
authors.forename: Alka
authors.initials: A
authors.lastname: Kanaya
authors.forename: Anne B
authors.initials: AB
authors.lastname: Newman
authors.forename: Sara E
authors.initials: SE
authors.lastname: Perry
authors.forename: Marjolein
authors.initials: M
authors.lastname: Visser
authors.forename: Macro
authors.initials: M
authors.lastname: Pahor
authors.forename: Tamara B
authors.initials: TB
authors.lastname: Harris
authors.forename: Barbara J
authors.initials: BJ
authors.lastname: Nicklas
mesh_terms: D000368:Aged; D000375:Aging / Q000502:physiology*; D015415:Biomarkers; D001823:Body Composition / Q000502:physiology*; D002097:C-Reactive Protein; D005260:Female; D006262:Health; D006801:Humans; D007249:Inflammation; D007376:Interleukin-2; D015850:Interleukin-6; D008297:Male; D017395:Plasminogen Activator Inhibitor 1; D014409:Tumor Necrosis Factor-alpha
chemical_list: D015415:Biomarkers; D007376:Interleukin-2; D015850:Interleukin-6; D017395:Plasminogen Activator Inhibitor 1; D014409:Tumor Necrosis Factor-alpha; D002097:C-Reactive Protein