CAT and fibromyalgia: Total antioxidant capacity (TAC) levels and levels of antioxidant enzymes, such as superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) have been reported to be significantly lower in patients with FM, and these reductions are inversely correlated with disease severity indices, including Fibromyalgia Impact Questionnaire scores, pain ratings and anxiety levels [30,56,57].