In a supplementation study carried out in Brazil that compared administration of ferrous sulfate (40 mg of iron per week) versus iron bis-glycinate chelate (3.8 mg per week as bis-glycinate chelate-enriched cookies) for 8 weeks on schoolchildren with anemia, the authors reported a significant increase in Hb concentration but no significant difference in the inter-group comparison. Here, GSTM1 is linked to anemia (phenotype).