Association of physical activity and renal parameters in subjects with and without metabolic syndrome in NHANES III

Purpose To determine association between physical activity and renal parameters including Glomerular Filtration rate, (GFR), Serum Creatinine, Blood Urea Nitrogen (BUN) and Proteinuria (Urine Albumin to Creatinine Ratio) in subjects with and without metabolic syndrome. Methods Subjects were classified as having metabolic syndrome if they had 3 of the following 5 components: high blood pressure, high serum triglycerides, high waist circumference, high plasma glucose, and low HDL-cholesterol. Physical activity was defined as the number of physical activity sessions in the prior 30 days as reported by the subjects on the questionnaire. Renal parameters were measured in laboratory analysis, and GFR was calculated from serum creatinine using the MDRD formula. Linear regression for the cross-sectional association of physical activity with the individual renal parameters was adjusted for age, race, sex, education, hypertension, diabetes, household size, family size, hypertension, diabetes and poverty income ratio. Results Analysis was performed on 15,705 subjects, of whom 53% were female, 42% non-Hispanic White, 27% African American, and 27% Mexican American. Metabolic syndrome was present in 20%. In unadjusted regression in subjects with vs. without metabolic syndrome, physical activity had mixed association with GFR (β = 0.02; p < 0.07 vs. β = 0.05; p < 0.0001); a significant positive association with serum Creatinine (β = 0.001; p = 0.0001 vs. β = 0.0007; p < 0.0001); mixed association with proteinuria (β = 0.0006; p = 0.21 vs. β = 0.0003; p = 0.002) and a significant positive association with BUN (β = 0.011; p = 0.04 vs. β = 0.005; p = 0.001). In adjusted regression in subjects with vs. without metabolic syndrome, physical activity had a significant positive association with GFR (β = 0.05; p < 0.0001 vs. β = 0.034; p < 0.0001); a mixed association with serum Creatinine (β = 0.005; p = 0.02 vs. β = 0.0001; p = 0.11); no association with proteinuria (β = 0.0002; p = 0.62 vs. β = 0.0001; p = 0.07) and no association with BUN (β = 0.004; p = 0.43 vs. β = 0.002; p = 0.09). Conclusion Higher levels of physical activity were associated with better GFR regardless of metabolic syndrome.