An stronger association between ferritin levels and metabolic syndrome was detected in studies adjusted by CRP [OR = 1.92 (95% CI: 1.61, 2.30; I2 = 78%)] compared to studies that did not adjust by CRP [OR = 1.52 (95% CI: 1.36, 1.69; I2 = 41%)]. This evidence concerns the gene CRP and metabolic syndrome.