CAT and depressive symptom measurement: As previously mentioned, studies have shown that the ‘oxidative–antioxidant’ function of the body in patients with depression is dysfunctional, mainly manifested in the increased concentration of oxygen free radicals and the abnormal activity of some antioxidant enzymes; namely, copper–zinc superoxide dismutase (CuZn SOD), glutathione peroxidase (GPX), and catalase (CAT) [137].