Study schema of the DIDS. Frequent blood donors who were iron (Fe) deficient (defined as ferritin <15 μg/L and zinc protoporphyrin >60 μMol/mol heme) but eligible for blood donation were recruited. Each participant donated an RBC unit, which was stored for 40 to 42 days, labeled with chromium-51 (⁵¹Cr), autologously transfused, and then assessed for 24-hour posttransfusion recovery. These individuals were then randomized to receive intravenous (IV) saline or iron. Approximately 145 days (129-162 days, with some pandemic-related exceptions) after randomization, participants donated a second RBC unit, which was likewise stored for 40 to 42 days, labeled with ⁵¹Cr, autologously transfused, and assessed for 24-hour posttransfusion recovery. Assessment of quality of life (via the RAND Health Survey) and cognitive function (via the Cognition Fluid Composite Score) was done before each blood donation and measurement of 24-hour posttransfusion recovery. Although iron repletion successfully corrected iron deficiency, on average, RBC units donated from iron-repleted individuals failed to display any difference in 24-hour posttransfusion recovery when compared with saline-treated controls. Secondary analyses, including quality of life and cognitive function, likewise found no difference between iron-repleted and saline-treated blood donor participants.