A preliminary analysis of within-subject variation in human serum oxidative stress parameters as a function of time

The aim of this study was to determine variability at both levels of two serum oxidative stress markers (lipid peroxides and carbonyl concentration) as well as total antioxidant capacity in humans as a function of time. Assays for oxidative stress and antioxidant capacity were repeated in the same individuals three times daily on four particular days over a period of 51 days. The results show a high variation within subject in the concentration of these markers not only when comparing the different days (the morning values can change up to 98%), but also during the day, where the evening values can increase up to 84% with respect to those of the morning. This suggests that several measurements are required to establish the typical oxidative stress status of an individual before studying the potential effect of treatments that possibly influence oxidative damage. The observed changes during the day allowed us to speculate about the optimum temporal antioxidant delivery regimes that minimize the imbalance between oxidants and antioxidants. In the study, only a few general aspects of basic lifestyle habits were controlled. However, the levels of these markers are sensitive to possibly a group of factors. This points to the necessity of using a much bigger population to establish the possible contribution of each lifestyle habits to the concentration of the markers.