Vegans, on the other hand, had lower indices of ferritin in two studies [16,17] (Δ in relation to OM −25%, 95% CI −44.0–−5.0), with a median of 29 ng/mL in vegans (IQR 22–42 vs. 38 in OM, IQR 26–52), lower levels of Hb (Δ in g/dL −0.37, 95% CI −0.69, −0.05) and erythrocytes (Δ in M/μL −0.23, 95% CI −0.33, −0.12) in one study [16], but similar Hb concentrations compared to the OM group in another study that assessed iron metabolism [17]. This evidence concerns the gene GSTM1 and ocular melanoma.