Summer Day/Night Gender Differences in Serum Total Antioxidant Capacity as a Methodological Pitfall in Human Antioxidant Research

Background: A dysregulation of the oxidant-antioxidant system has been described in several medical conditions. The total antioxidant capacity (TAC) is one measure of the antioxidant capacity of a system. Circadianity is a biological characteristic of hormones such as melatonin or cortisol. There is little information about TAC circadian rhythm in healthy subjects. Objective: Assessing if healthy subjects present day/night serum TAC changes. Methods: Blood of48 men and 49 women were drawn at 12:00 and 00:00 hours in summer. Serum TAC was measured by the ABTS radical cation technique. TAC results are expressed as mmol of trolox/L (mean ± SD). Results: Men had higher serum TAC concentrations at midday than midnight (0.88±0.18 vs. 0.75±0.19, p<0.001). Women did not have a day/night difference in TAC concentrations (12:00: 0.78±0.19 vs. 0.76±0.19, p: NS). Conclusions: Methodological pitfalls may be committed if those gender day/night differences are not taken into account when researching about this biological parameter.