Associations between time spent sitting and cancer-related biomarkers in postmenopausal women: an exploration of effect modifiers

Abstract

Purpose: 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.

Fig. 1

Graphs presenting distributions of adjusted mean levels of the cancer-related biomarkers by quartiles of time spent sitting and selected covariate in participants enrolled in the ancillary study of the Women’s Health Initiative Observational Study at Baylor College of Medicine and Wake Forest University School of Medicine from February 1995 to July 1998 (Note: Quartile cut-points: Q1 <4 h/day; Q2 = 4–<6 h/day; Q3 = 6–<8 h/ day; Q4 ≥ 8 h/day; CRP, C-reactive protein; IGF-I, insulin-like growth factor-I; IGFBP-3, IGF-binding protein-3; IL-6, interlukin-6; MET, metabolic equivalent) a1 Distributions of adjusted mean levels of IGF-I by sitting hours stratified by race. a2 Distributions of adjusted geometric mean levels of IL-6 by sitting hours stratified by race. b1 Distributions of adjusted mean levels of IGFBP-3 by sitting hours stratified by physical activity. b2 Distributions of adjusted geometric mean levels of insulin by sitting hours stratified by physical activity. c1 Distributions of adjusted mean levels of leptin by sitting hours stratified by estrogen use. c2 Distributions of adjusted geometric mean levels of CRP by sitting hours stratified by estrogen use. d Distributions of adjusted mean levels of C-peptide by sitting hours stratified by history of hypertension