GSTM1 and chronic kidney disease: In chronic kidney disease (CKD) patients, some nonrandomized intervention studies could already show that intravenous administration of activated vitamin D (1,25-dihydroxyvitamin D3 = 1,25(OH)2D3) is associated with an increase in Hb levels within 12 months of treatment and a reduced need for erythropoietin (EPO) [16, 17].