Short-term changes in daily movement behaviour influence C-reactive protein in healthy, middle-aged women

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Willoughby, Taura N.
University of Lethbridge. Faculty of Arts and Science
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Lethbridge, Alta : University of Lethbridge, Dept. of Kinesiology and Physical Education
Despite growing awareness of the health consequences of sedentary time (ST), the underlying physiological mechanisms are poorly understood. C-reactive protein (CRP), a marker of systemic inflammation, represents a potential link between ST and adverse health. It has also become apparent that prolonged, uninterrupted bouts of ST are particularly harmful to health. The primary purpose of this thesis was to explore the effect of (a) increased ST and (b) increased physical activity (PA) on salivary CRP in healthy, middle-aged women. A secondary objective was to examine how the pattern of activity changes in response to these behavioural interventions. After completing a 7-day preliminary assessment of daily step count, ST, and PA, 20 healthy, middle-aged women were randomly assigned to one of two 10-day interventions, either sedentary or active. The sedentary group reduced their step count to <5000 steps/day. The active group added 3,000 steps/day to their preliminary average. During both the preliminary assessment and intervention period, participants wore a pedometer to monitor their daily step count and an accelerometer to objectively assess their activity profile. Salivary CRP samples were taken during the preliminary assessment, pre-intervention, and post-intervention. During the intervention, the sedentary group (n=9; 49.65.6 yrs; 28.43.5 kg•m-2) significantly increased ST by 70 minutes/day, and decreased both light physical activity (LPA) and moderate-to-vigorous physical activity (MVPA). They also increased the number of prolonged sedentary bouts (p = 0.004) and decreased the frequency of iv interruptions to ST (p = 0.006). The active group (n=10; 49.95.2 yrs; 26.63.7 kg•m-2) increased MVPA by 19.4 minutes/day, but there was no change in ST, LPA, or the pattern of ST accumulation. After 10 days of behavior change, CRP increased by 31% in the sedentary group (p<0.05) and decreased by 22% in the active group (p<0.01). These results suggest that CRP, and thus inflammation, may represent a physiological link between movement behavior and health in middle-aged women. The decrease in CRP in the active group despite no change in ST challenges current data that shows ST impacts health independent of MVPA. Importantly, interventions focused on increasing MVPA may not effectively reduce ST.
C-reactive protein , inflammation , physical activity , sedentary time