The goal of this pilot study is to test whether the microbiome is affected by intravenous iron repletion.

The colonic microbiome, the community of bacteria living in our gut, is essential in human health and disease. Iron is an essential nutrient for both bacteria and humans. 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. The goal is to conduct a prospective, double-blind, randomized controlled trial, recruiting 60 healthy regular donors who meet donation standards, while exhibiting iron-deficient erythropoiesis by laboratory test criteria. In this ancillary study, we will determine what effect donor iron deficiency and IV iron repletion have on the gut microbiome.

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.