The goal of this clinical trial is to evaluate, if a change in dosing strategy in oral iron supplementation from leads to an improvement of iron absorption and consequently a faster therapy in patients with iron deficiency. The main question the study aims to answer is: Does a treatment effect (measured by change in hemoglobin after 12 weeks of treatment) exist between daily oral iron supplementation and interval administration (every second day)? Participants will receive oral iron supplementation every second day with double the standard dose (intervention group). Researchers will compare this group with the active control group, that receives oral iron supplementation every day with the standard dose. Participants will present for three patient visits (at baseline, after 6 and after 12 weeks of treatment).