Our data show that at higher-than-normal levels of Hb, increasing deciles of Hb concentration were significantly associated with MetS across all sex subgroups in both ethnicities, with the highest deciles resulting in up to three times greater risk than the reference group [Taiwanese HC: OR = 3.17 (95% CI, 2.75–3.67) for Hb ≥ 16.5 g/dL in men, OR = 3.11 (2.78–3.47) for Hb ≥ 14.5 g/dL in women; European Whites: OR = 1.89 (1.80–1.98) for Hb ≥ 16.24 g/dL in men, OR = 2.35 (2.24–2.47) for Hb ≥ 14.68 g/dL in women]. This evidence concerns the gene GSTM1 and metabolic syndrome.