Big effect
Iron supplements slashed blood donor deferral risk by 61% in a meta-analysis — but the evidence is only moderate and side effects like constipation were common.
This is one of the first pooled analyses on iron for donor deferral, and the effect is unusually large, but the moderate certainty and frequent GI side effects mean the trade-off is real — it’s not a simple win.
Blood donors who took iron supplements were about 61% less likely to be turned away for low hemoglobin at their next visit, according to a meta-analysis of 7 studies involving 1,647 people. However, the researchers rated the evidence as only moderate certainty, and oral iron often caused abdominal pain, constipation, or diarrhea — so the benefit comes with a clear downside.
Where this fits in the evidence
This is among the first studies we've indexed on Iron for Reduced Deferral Rate — treat it as an early signal until more research accumulates.
The study
- Meta-Analysis
- n = 7,475
- 2026-06-04
- The Cochrane database of systematic reviews
This is a plain-language summary of a research finding, not medical advice. Pillser surfaces research signals to help you decide what's worth investigating — always consult a qualified professional before changing what you take.