Katsumata et al. [17], in a rat model, have reported that iron deficiency decreased the levels of 1,25-dihydroxycholecalciferol and osteocalcin concentrations, suggesting that hydroxylation of vitamin D is dependent on iron, and hence iron-deficient rats had lower concentrations of the active form of vitamin D. In the present study, ferritin level and Hb level were the most significant factors affecting vitamin D levels. The gene discussed is GSTM1; the disease is Iron deficiency anemia.