Circadian Profiles of XOR Isoforms and Melatonin-Cosinor Analysis The combined 24 h cosinor analysis revealed strong, highly significant rhythmicity in plasma melatonin (global p < 10 −6 ), with nearly identical acrophases in women and men (≈3.8–3.9 h).
In women, however, the Friedman ANOVA test did not show statistically significant differences, although the p -value approached significance ( p = 0.054), with Kendall’s coefficient of concordance at 0.18.
The near-significant trend observed for XDH ( p = 0.094) might indicate a weak endogenous rhythm, consistent with its antioxidative role and earlier studies describing partial circadian control of redox enzymes such as superoxide dismutase, catalase, and glutathione peroxidase [ 9 , 65 , 67 ].