This is a trial with an observational and an interventional arm, in patients with moderate to severe anemia and control subjects. The main purposes of this study is to phenotype the scope of neurocognitive deficits from iron deficiency anemia (IDA) in adult women, determine derangements in cerebral perfusion, vascular reactivity, functional connectivity, and blood brain barrier permeability in adult-onset IDA and relate them to neurocognitive deficits, as well as determine the reversibility and durability of both the physiologic and neurocognitive derangements by iron replacement therapy. All eligible subjects will be asked to provide informed consent before participating in the study.