Plasma antioxidant capacity among middle-aged men: The contribution of uric acid

Objective. Although assays of plasma antioxidant capacity encompass interactions between various antioxidants, uric acid concentration can exert a predominant effect on results. Therefore, individual differences in uric acid concentration may explain a many of the differences in antioxidant capacity. The objective of this study was to measure the antioxidant capacity of plasma samples with and without uric acid in order to provide more information about how the concept of antioxidant capacity could be applied. Material and methods. Antioxidant capacity was measured using an enhanced chemiluminescence assay, and uric acid was removed from the samples using uricase. Results. Antioxidant capacity was positively correlated with uric acid concentration, body mass index, waist circumference, abdominal sagittal diameter and the concentrations of insulin and triglycerides. These correlations were not evident when uric acid was eliminated from the sample, but antioxidant capacity was correlated with lipid concentration; this may partly reflect tocopherols that are transported by lipid molecules. Conclusions. The significance of the contribution of uric acid to the antioxidant capacity could differ according to the type of study. Antioxidant capacity measurements in cross-sectional studies may be presented both with and without the contribution of uric acid, because the absence of such data complicates interpretation of results when different populations are compared.