SOD1 and migraine disorder: The Pearson correlation analysis revealed significant strong negative correlations between the number of headache days per month and serum concentrations of the two antioxidant enzymes, CAT (r = − 0.60, P-value< 0.001) and SOD (r = − 0.50, P-value< 0.001), and the serum antioxidant capacity measured by the TEAC assay (r = − 0.61, P-value< 0.001) among 71 subjects suffering from migraine.