Zinc levels after iron supplementation in patients with chronic kidney disease

Abstract

Objective The goal of this study was to evaluate the effects of iron supplementation on zinc distribution in nondialyzed chronic kidney disease (CKD) patients. Design Prospective nonrandomized observational study. Setting Outpatients of the Nephrology Division at Federal University of São Paulo. Patients Zinc and iron status of 38 nondialyzed patients (63% male; creatinine clearance, 34.5±13.3 mL/min/1.73 m 2) was evaluated before and after 3 intramuscular injections of 100 mg iron each. Main outcome measures The following parameters were analyzed: erythrocytes and plasma zinc, zinc protoporphyrin (ZPP), plasma ferritin, transferrin saturation (TFS), and total iron. The patients’ diets were analyzed by the Association of Official Analytical Chemists method for macronutrients, and neutron activation analysis was used for iron and zinc concentration determinations. Results Ferritin and TFS increased from 86.3±67.5 ng/mL to 105.4±63.7 ng/mL and from 19.5±7.4% to 23.2±6.7% ( P < .05), respectively, after iron supplementation. Absolute iron deficiency (ferritin <100 μg/L and TFS <20%) was present in 41% of the patients and decreased to 15.7% after iron treatment. In comparison with baseline values (76.4±16.7 μg/dL), there were no significant changes in plasma zinc levels, but after supplementation the number of patients with low plasma zinc levels decreased from 46.1% to 23.7% ( P = .08). At baseline, erythrocyte zinc was 49.0±7.6 μg Zn/gHb, and 76.3% of the patients had high erythrocyte zinc concentration. After iron treatment, erythrocyte zinc decreased to 45.5±7.3 μg Zn/gHb ( P = .001). No significant change was observed in ZPP concentration. The analysis of the diet showed energy and protein intakes of 26.2±7.1 kcal/kg/day and 0.89±0.2 g/kg/day, respectively, and a low intake of both iron and zinc. Conclusions This study suggests that iron deficiency may contribute to the inadequate distribution of zinc in patients with CKD and that iron supplementation may decrease the abnormal elevated erythrocyte zinc levels of these patients.