Background: The association between physical activity and renal function in subjects with and without metabolic syndrome was examined.
Methods: Renal function was evaluated in subjects of the Third National Health and Nutrition Examination Survey by using calculated glomerular filtration rate (GFR) and urine microalbuminuria (urine albumin-creatinine ratio). These parameters were studied as a function of physical activity by using a 1-month recall. Measures included activity variety, number of different types of exertion; activity frequency, the sum of all activity periods; and metabolic equivalent (METS), the total sum of energy expenditures. Individuals were segregated into those with metabolic syndrome and no metabolic syndrome; ages 18 to 44, 45 to 55, and older than 55 years; men and women; and 3 racial groups: Caucasians, African Americans, and Mexican Americans.
Results: Younger individuals, men, and those with higher levels of education had a lower risk for metabolic syndrome. The groups also had better renal function, measured by using GFR and urinary protein. Those without metabolic syndrome performed larger numbers of activity varieties in the unadjusted analysis (2 +/- 2 [SD]; n = 11,184) compared with those with metabolic syndrome (1 +/- 1; n = 2,569; P < 0.0001). Similar differences in activity frequency and METS also were observed. Conversely, GFR correlated with activity variety and METS, but negatively with activity frequency in those without metabolic syndrome after adjustment for confounders. In subjects with metabolic syndrome, GFR correlated only with activity variety. Variable observations were made among ages, sexes, and races.
Conclusion: There is a clear association between physical activity and GFR, particularly in subjects without metabolic syndrome; however, cross-sectional analysis precludes establishing causality.