In agreement, T-AOC in saliva was reduced in smokers compared with non-smokers (Bakhtiari et al., 2015), and the activities of SOD and catalase, the most important antioxidant enzymes, were reduced in serum of smokers and COPD patients compared to normal controls (Tavilani et al., 2012). This evidence concerns the gene SOD1 and chronic obstructive pulmonary disease.