GSTM1 and anemia: Another meta-analysis of post-only studies with concurrent control determined that YYB was associated with an increase of 4.43 g/L (95% CI:1.55, 7.30) in Hb concentration, and reductions in the prevalence of anemia (risk ratio (RR) = 0.55; 95% CI: 0.45, 0.67) [28].