Physical Activity and Mortality in Chronic Kidney Disease (NHANES III)

Background and objectives: Chronic kidney disease (CKD) is associated with impaired physical activity. However, it is unclear whether the associations of physical activity with mortality are modified by the presence of CKD. Therefore, we examined the effects of CKD on the associations of physical activity with mortality.Design, setting, participants, & measurements: This was an observational study of 15,368 adult participants in the National Health and Nutrition Examination Survey III; 5.9% had CKD (eGFR < 60 ml/min per 1.73 m²). Based on the frequency and intensity of leisure time physical activity obtained by a questionnaire, participants were divided into inactive, insufficiently active, and active groups. Time to mortality was examined in Cox models, taking into account the complex survey design.Results: Inactivity was present in 13.5% of the non-CKD and 28.0% of the CKD groups (P < 0.001). In two separate multivariable Cox models, compared with the physically inactive group, hazard ratios (95% confidence intervals) of mortality for insufficiently active and active groups were 0.60 (0.45 to 0.81) and 0.59 (0.45 to 0.77) in the non-CKD subpopulation and 0.58 (0.42 to 0.79) and 0.44 (0.33 to 0.58) in the CKD subpopulation. These hazard ratios did not differ significantly between the CKD and non-CKD subpopulations (P > 0.3).Conclusions: Physical inactivity is associated with increased mortality in CKD and non-CKD populations. As in the non-CKD population, increased physical activity might have a survival benefit in the CKD population.There are >16 million U.S. adults with stage III and IV chronic kidney disease (CKD) (1), yet there are only ∼400,000 in stage V CKD. A vast majority of those with moderate CKD die before they reach ESRD (2). However, the current focus of the providers taking care of the stage III and IV CKD population is on measures to slow the progression of kidney disease rather than on measures that could reduce the mortality in this population.Increased physical activity is associated with better survival in the general population. A previous analysis of the Modification of Diet in Renal Disease (MDRD) Study suggested that higher levels of physical activity were not significantly associated with reduced mortality in the CKD population (3). To our knowledge, there are no other data on exercise and survival in the CKD population. Therefore, we examined whether the presence of CKD modifies the association of exercise with mortality in the National Health and Nutrition Examination Survey (NHANES) III.