Maintaining optimal iron levels in blood donors is important, especially when 25-35 percent of regular donors develop an iron deficiency that can lead to fatigue and anemia. In a study of blood donors, researchers discovered that individuals who received a low-dose iron supplement returned to their pre-donation iron levels between 7 and 18 weeks earlier than those who did not receive a supplement. Surprisingly, two-thirds of those who did not receive iron supplements failed to regain their pre-donation iron levels by week 24.
National Institutes of Health, February 2015