Effect of Anemia on Physical Function and Physical Activity in CKD: The National Health and Nutrition Examination Survey, 1999–2016

KEY POINTS: In a large sample representative of the US adult noninstitutionalized population, among participants with CKD stages 3–5, anemia was associated with a significantly lower level of physical activity. The presence of CKD and anemia showed a positive interaction on physical functioning outcomes. Among participants with CKD, physical functioning was worse in patients with anemia compared with those without anemia. BACKGROUND: CKD is a major public health problem worldwide. Anemia, a frequent and treatable complication of CKD, is associated with decreased physical functioning and physical activity. The objective of this study was to evaluate the joint association of CKD and anemia with physical functioning and physical activity in a representative sample of the US population. METHODS: Cross-sectional study using the National Health and Nutrition Examination Survey (NHANES) 1999–2016 for physical functioning outcomes (N=33,300) and NHANES 2007–2016 for physical activity (N=22,933). The NHANES physical functioning questionnaire included 19 items. The NHANES physical activity questionnaire captured work-related, leisure-time, and sedentary activities. Higher physical functioning scores represent worse function. CKD was classified using Kidney Disease Outcomes Quality Initiative 2002 criteria, and anemia was defined using the World Health Organization criteria. RESULTS: The adjusted mean differences (95% confidence interval) in overall physical functioning score comparing participants with anemia with those without anemia among participants with no CKD, CKD stages 1–2, and stages 3–5 were 0.5 (−0.1 to 1.0), 1.5 (0.2 to 2.8), and 3.6 (2.0 to 5.2). Anemia and CKD showed a supra-additive interaction for all physical functioning outcomes among participants in CKD stages 3–5. The prevalence of high physical activity was also lower in participants with anemia compared with those without anemia among participants in CKD stages 3–5 (adjusted prevalence ratio, 0.74; 95% confidence interval, 0.54 to 1.01). CONCLUSIONS: CKD and anemia were associated with impairments in physical functioning and reduced physical activity. For physical functioning outcomes, the combined presence of CKD and of anemia showed a stronger effect than what was expected from their independent effects.