This pilot study is designed to investigate (1) whether getting iron treatment affects iron in the brain and (2) how getting iron treatment affects brain functions when it is performing specific cognitive tasks. By cognitive tasks, it means tasks that involve perceiving, representing, or assessing things. The specific cognitive tasks used here will involve tests of memory and processing speed.

Iron, the most abundant metal in the brain, is vital for multiple cellular processes, including neurotransmitter synthesis, neuron myelination, and mitochondrial function. In the United States, of the donors who provided the ~15 million units of red blood cells that were collected for transfusion, 69% were repeat donors. Although iron deficiency is surprisingly prevalent in first-time donors, its prevalence is even higher in these particularly altruistic frequent donors, (i.e., up to 49% and 66% of male and female repeat donors, respectively), manifested as iron depletion or iron-deficient erythropoiesis. Iron deficiency from blood donation is associated with fatigue, restless leg syndrome, decreased physical endurance and work capacity, and impaired concentration, attention, and other neurocognitive functions; however, these conclusions are not based on definitive studies and have not yet changed blood donation policy. This study is to collect data through noninvasive procedures routinely employed in clinical practice to better understand how iron treatment may affect brain functions.

Inclusion Criteria:

• Current participant of the associated randomized controlled trial conducted at Columbia University Medical Center (therefore invited to participate in this optional ancillary study).

Exclusion Criteria:

• Not a current participant of the associated randomized controlled trial conducted at Columbia University Medical Center.

Subjects with iron deficiency from blood donation will be recruited over 5 years in the associated randomized controlled trial conducted at Columbia University Medical Center.