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