PON1 and psoriasis: In sub-group analysis, reported in Fig. 6, there was a significant psoriasis-associated decrease in serum PON-1 activity in European studies (SMD = − 2.34; 95% CI − 3.76 to − 0.91, p = 0.001; I2 = 94.8%, p < 0.001) but not in studies conducted in Asia (SMD = − 1.06; 95% CI − 2.20 to 0.08, p = 0.07; I2 = 95.1%, p < 0.001) or America (SMD = 0.17; 95% CI − 0.76 to 1.10, p = 0.72; I2 = 89.4%, p = 0.002).