Iron
Research reviewed: Up until 03/2026
Iron is a dietary supplement with 4 published peer-reviewed studies involving 1,399 participants, researched for Fatigue & Iron Deficiency Without Anaemia, Blood Donors — Iron Recovery & Deficiency Prevention, General Health.
Evidence at a Glance
Strength is scored by study design, sample size, study type, and outcomes
Fatigue & Iron Deficiency Without Anaemia
ModerateBlood Donors — Iron Recovery & Deficiency Prevention
StrongGeneral Health
ModerateResearch Visualised
Visual breakdown of the clinical data.
Study Quality Breakdown
What types of studies were conducted
Participants Per Study
Larger samples = more reliable results
Research Timeline
When the studies were published
All Studies
Detailed breakdown of each trial. Click to expand.
Fatigue & Iron Deficiency Without Anaemia
To determine the effects of oral iron supplementation on fatigue in non-anaemic menstruating women with low ferritin (iron stores) who present with unexplained tiredness
Study Type
Multicentre, parallel, randomised controlled, observer-blinded trial
Purpose
To determine the effects of oral iron supplementation on fatigue in non-anaemic menstruating women with low ferritin (iron stores) who present with unexplained tiredness
Dose
80 mg elemental iron/day (ferrous sulphate) or placebo
Participants
198 women aged 18–53 years
Duration
12 weeks
Results
Researchers observed that fatigue scores decreased significantly more in the iron group compared to placebo. The CPPS score (a questionnaire that measures how tired someone feels in daily life; higher scores mean more fatigue) significantly dropped by 47.7% with iron versus 28.8% with placebo—a difference of −18.9%. Haemoglobin (the part of blood that carries oxygen) also significantly increased by +0.32 g/dL, showing better oxygen delivery in the body. Ferritin (a marker of iron stores; low levels mean low reserves) increased by +11.4 µg/L, and sTfR (a marker that rises when the body lacks usable iron; lower is better) decreased by −0.54 mg/L, indicating improved iron availability in the body. However, there were no significant changes in quality of life, depression, or anxiety scores.
Blood Donors — Iron Recovery & Deficiency Prevention
To determine the optimal dose and frequency of iron supplementation for whole-blood donors with low ferritin, comparing 30 mg vs 60 mg and daily vs alternate-day dosing, and assessing whether iron supplementation can replace the need for extended donation intervals
Study Type
Double-blind, randomised, placebo-controlled trial
Purpose
To determine the optimal dose and frequency of iron supplementation for whole-blood donors with low ferritin, comparing 30 mg vs 60 mg and daily vs alternate-day dosing, and assessing whether iron supplementation can replace the need for extended donation intervals
Dose
Ferrous bisglycinate capsules: 0 mg (placebo), 30 mg, or 60 mg of elemental iron, administered either daily or on alternate days for 56 days; six study groups in total
Participants
830 regular whole-blood donors (464 female, 366 male; average age ~44 years)
Duration
56 days
Results
Researchers observed that all four iron supplementation groups significantly reduced the risk of iron deficiency (ferritin < 15 µg/L, where ferritin is a measure of iron stored in the body; low levels mean low iron reserves) compared to placebo after 56 days. The odds ratios ranged from 0.60 to 0.65, meaning those taking iron were about 35–40% less likely to become iron deficient. The most effective was daily 60 mg iron, which reduced the risk of low ferritin (15–30 µg/L) by 48%. Low haemoglobin (the oxygen-carrying part of blood; low levels can cause fatigue and weakness) was also significantly less common in all iron groupsImportantly, there were no increases in stomach-related side effects, and participants were just as willing to return, showing the supplement was well tolerated even at higher doses.
To determine the effect of low-dose oral iron supplementation on the speed of haemoglobin and ferritin recovery in blood donors following a standard unit donation
Study Type
Randomised, non-blinded clinical trial
Purpose
To determine the effect of low-dose oral iron supplementation on the speed of haemoglobin and ferritin recovery in blood donors following a standard unit donation
Dose
One tablet of ferrous gluconate (37.5 mg elemental iron) daily or no iron supplement following a single whole blood donation
Participants
215 blood donors aged 18–79 years
Duration
168 days (24 weeks)
Results
Researchers observed that in people with low iron stores, haemoglobin (the part of blood that carries oxygen) recovery was significantly higher in those taking iron, reaching 106.0% of their original levels, meaning they recovered to above their pre-donation levels. In contrast, those without iron supplementation dropped to 98.1%, meaning they actually fell below normal and became mildly anaemic (low red blood cells). Ferritin (a measure of iron stored in the body) also recovered much faster, taking a median of 76 days with iron versus more than 168 days without supplementation. Without iron, 67% of donors did not recover their iron stores within the study period
General Health
To assess the effect of iron supplementation on fatigue in nonanemic menstruating women with low iron stores
Study Type
Randomized, double-blind, placebo-controlled trial
Purpose
To assess the effect of iron supplementation on fatigue in nonanemic menstruating women with low iron stores
Dose
80 mg elemental iron daily (as ferrous sulfate)
Participants
156 nonanemic menstruating women aged 18-53 years with ferritin levels <50 μg/L
Duration
12 weeks
Results
Iron supplementation significantly reduced fatigue by ~50% from baseline, with 19% greater improvement compared to placebo. Effect was dose-dependent
How They Measured It
Fatigue Severity Scale, serum ferritin, hemoglobin levels
Frequently Asked Questions
Common questions about Iron research
There are currently 4 peer-reviewed studies on Iron (Iron), involving 1,399 total participants. Research covers Fatigue & Iron Deficiency Without Anaemia, Blood Donors — Iron Recovery & Deficiency Prevention. The overall evidence strength is rated as Strong.
The evidence is currently rated as "Strong Evidence". This rating is based on study design quality (randomisation, blinding, placebo controls), sample sizes, study types (4 human studies), and reported outcomes.
Iron has been researched for: Fatigue & Iron Deficiency Without Anaemia, Blood Donors — Iron Recovery & Deficiency Prevention. Each area has its own body of evidence which you can explore in the study breakdowns above.
Yes, 4 out of 4 studies are human trials. Human trials carry more weight in our evidence scoring system.
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