Long-term melatonin administration enhances the antioxidant potential of human plasma maintained after discontinuation of the treatment

We investigated the effect of long-term oral melatonin administration on the antioxidant capacity of plasma. The study was performed on healthy volunteers divided into two groups: the control group (without melatonin treatment) and the study group treated with 6 mg of melatonin per day for two weeks, 2 hours before bedtime. Blood samples were drawn: before melatonin administration, on the 7(th) and 14(th) day of melatonin treatment and on the 10(th) day after the last dose of melatonin. It was shown that oral administration of melatonin increases plasma antioxidant ferric reducing ability (FRAP assay) (p < 0.05) and DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging (p < 0.01), and decreases thiobarbituric acid reactive substances (TBARS) (p < 0.05) and DNA damage (p < 0.001). This protective effect is maintained for at last 10 days after discontinuation of the treatment. The present work highlights that the antioxidant capacity of plasma was significantly higher on the 10(th) day after the discontinuation of melatonin treatment than on the 14(th) day of its administration. Our findings indicated that a long-term oral melatonin administration maintained the increased antioxidant capacity of plasma and prevented oxidative damage to DNA after hormone administration was discontinued.