Association of self-reported physical activity with laboratory markers of nutrition and inflammation: the Comprehensive Dialysis Study

Abstract

Objective: Patients on dialysis maintain extremely low levels of physical activity. Prior studies have demonstrated a direct correlation between nutrition and physical activity but provide conflicting data on the link between inflammation and physical activity. Using a cohort of patients new to dialysis from the Comprehensive Dialysis Study (CDS), we examined associations of self-reported physical activity with laboratory markers of nutrition and inflammation.

Design, setting, and patients: Between June 2005 and June 2007, CDS collected data on self-reported physical activity, nutrition, and health-related quality of life from patients starting dialysis in 296 facilities located throughout the United States. Baseline serum samples were collected from participants in a nutrition sub-study of CDS.

Measures: Serum albumin and prealbumin were measured as markers of nutrition, and C-reactive protein (CRP) and α-1-acid glycoprotein as markers of inflammation. Self-reported physical activity was characterized by the maximum activity score (MAS) and adjusted activity score (AAS) of the Human Activity Profile.

Results: The mean age of participants in the analytic cohort (n = 201) was 61 years. The MAS and AAS were below the 10th and first percentile, respectively, in comparison with healthy 60 year-old norms. Both activity scores were directly correlated with albumin (r(2) = 0.3, P < .0001) and prealbumin (r(2) = 0.3, P < .0001), and inversely correlated with CRP (AAS: r(2) = -0.2, P = .01; MAS: r(2) = -0.1, P = .08). In multivariate analyses adjusting for age, gender, race/ethnicity, diabetes status, and center, both activity scores were directly correlated with prealbumin and inversely correlated with CRP.

Conclusions: Patients new to dialysis with laboratory-based evidence of malnutrition and/or inflammation are likely to report lower levels of physical activity.

Copyright © 2011 National Kidney Foundation, Inc. All rights reserved.

Figures

Figure 1. Analytic cohort for current study in relation to larger Comprehensive Dialysis Study

A total of 265 participants agreed to participate in the nutrition sub-study and provide serum samples. Of these, data were available from both patient questionnaires and serum samples from 225 participants. The current analysis is limited to 201 participants who completed the questionnaire within 120 days of providing serum samples. Abbreviations: CDS-Comprehensive Dialysis study; HAP-Human activity profile.

Figure 2. Correlation of AAS and MAS with laboratory markers

Activity scores can range from 0-94. Pearson r2 and corresponding p values are displayed. Significant correlation was seen between AAS and albumin, prealbumin and CRP; and between MAS and albumin and prealbumin. Abbreviations: AAS-Adjusted activity score; MAS-Maximal activity score; CRP-C-reactive protein.

Figure 3. Relationship between AAS, albumin or prealbumin and ln CRP

In unadjusted analyses, AAS levels were highest when prealbumin or albumin were high and CRP low. Lowest AAS levels were seen when albumin or prealbumin were low and ln CRP was high. In Panel 2, AAS levels remained relatively low when ln CRP was high, despite high concentrations of prealbumin. Abbreviations: AAS-adjusted activity score, Ln-Natural log; CRP-C-reactive protein.