GSTM1 and anemia (phenotype): Vitamin B2 (riboflavin) deficiency may also contribute to anemia through its effects on iron metabolism, including a decrease in iron absorption, an increase in intestinal loss of iron or the impairment of iron utilization for Hb synthesis.16 In the second study by Dillon et al, vitamin B2 status was positively associated with Hb concentrations and plasma ferritin.