title: Associations between time spent sitting and cancer-related biomarkers in postmenopausal women: an exploration of effect modifiers.
abstract: OBJECTIVE
  Despite evidence that prolonged periods of sitting may influence biological mediators of cancer development, few studies have considered these relationships in a cancer-specific context.
  
  
  METHODS
  This cross-sectional study included 755 postmenopausal women enrolled in an ancillary study of the Women's Health Initiative. Plasma levels of Insulin-like growth factor-I (IGF-I), IGF-binding protein-3, leptin, insulin, C-peptide, C-reactive protein (CRP), and Interleukin (IL)-6 were measured. The time spent sitting per day was categorized as quartiles (Qs). The relationships between sedentary time and biomarkers were modified by race, physical activity, and exogenous estrogen use.
  
  
  RESULTS
  IGF-I levels among African American (AA) women were higher than those of white women across the Qs of sedentary time. Likewise, IL-6 levels in AA women were higher than those in white women at Q3 and Q4 of sedentary time. IGFBP-3 levels were higher and insulin levels were lower across the Qs of sedentary time among women meeting guidelines for physical activity than women who were not. Additionally, CRP levels were higher among estrogen users than nonusers at Q1, Q2, and Q4 of sedentary time.
  
  
  CONCLUSIONS
  These results suggest that relationship between time spent sitting and cancer-related biomarkers may not be simply linear, but differ in the context of effect modifiers.
authors.affiliation: Department of Behavioral and Community Health, School of Public Health, University of North Texas Health Science Center, Fort Worth, TX, USA.
authors.forename: Raheem J
authors.initials: RJ
authors.lastname: Paxton
authors.forename: Su Yon
authors.initials: SY
authors.lastname: Jung
authors.forename: Mara Z
authors.initials: MZ
authors.lastname: Vitolins
authors.forename: Jenifer
authors.initials: J
authors.lastname: Fenton
authors.forename: Electra
authors.initials: E
authors.lastname: Paskett
authors.forename: Michael
authors.initials: M
authors.lastname: Pollak
authors.forename: Jennifer
authors.initials: J
authors.lastname: Hays-Grudo
authors.forename: Stephen D
authors.initials: SD
authors.lastname: Hursting
authors.forename: Shine
authors.initials: S
authors.lastname: Chang
mesh_terms: D001741:Black or African American; D000368:Aged; D014408:Biomarkers, Tumor / Q000097:blood*; D002096:C-Peptide / Q000378:metabolism; D002097:C-Reactive Protein / Q000378:metabolism; D003430:Cross-Sectional Studies; D015914:Estrogen Replacement Therapy; D005260:Female; D006801:Humans; D007328:Insulin / Q000097:blood; D018972:Insulin-Like Growth Factor Binding Protein 3 / Q000097:blood; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D020738:Leptin / Q000097:blood; D008875:Middle Aged; D009369:Neoplasms / Q000097:blood / Q000453:epidemiology* / Q000208:ethnology / Q000209:etiology; D017698:Postmenopause; D057185:Sedentary Behavior; D014481:United States / Q000453:epidemiology; D044465:White People; D016387:Women's Health
chemical_list: D014408:Biomarkers, Tumor; D002096:C-Peptide; C508600:IL6 protein, human; D007328:Insulin; D018972:Insulin-Like Growth Factor Binding Protein 3; D015850:Interleukin-6; D020738:Leptin; D007334:Insulin-Like Growth Factor I; D002097:C-Reactive Protein