Reviews/Iron Status/Iron cuts fatigue in non-anaemic women
Func · IRON-FUNC-01 · v2
Borderline: within 4 points of the Likely/Uncertain boundary, so a re-grade could land either side.
Women who are low in iron but not anaemic often feel tired, and this review asked whether giving them iron makes them feel less fatigued. Several placebo-controlled trials in exactly this group point the same way: iron lowered tiredness more than a dummy pill in [1], [8] and [3], and a female subgroup of athletes felt less tired in [10]. But the largest, best-controlled trial that used iron given by drip [2] found no clear overall benefit, with improvement showing up only in the women whose iron stores were most depleted. The improvements that did appear were modest, several studies were small, and one trial in athletes [6] found no effect on tiredness at all. Because fatigue is something people rate themselves, and the trials used different iron types, doses and durations, the panel treated the evidence as supportive but not settled.
Three placebo-controlled trials in the exact population report reduced fatigue with iron: [1] (fatigue score fell 47.7% with iron vs 28.8% with placebo, difference -18.9%, 95% CI -34.5 to -3.2; p=0.02), [8] (fatigue improved in the iron arm but not placebo, p<0.05, n=26) and [3] (fatigue score fell after iron, p=0.05, n=164). Indirect support comes from [10], where female athletes on low-dose iron showed reduced tired feeling after exercise (P=0.05) and lower total mood disturbance (P=0.016), and from [9], where fatigue improved more with intravenous than oral iron in pregnant women. The direction is consistent across independent teams in France, Switzerland, Pakistan and Australia. Against this, [2] (n=90) found the overall between-group fatigue effect non-significant (P=.07), and [6] (n=22) found no difference in perceived-exertion fatigue. The contested point: The evidence divides on whether the benefit holds across all non-anaemic iron-deficient women or only in those most depleted: [2] was overall null (P=.07) with a clear effect confined to the ferritin ≤15 subgroup (fatigue fell 1.8 vs 0.4, P=.005). It also divides on measurement, since [1] improved a fatigue scale but not quality of life (p=0.2), and [3]'s significance is a within-group post-intervention change rather than a clean placebo contrast.
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The best-controlled direct trial [2] found no significant overall fatigue effect (P=.07); benefit existed only in the ferritin ≤15 subgroup, so the claim as stated (all non-anaemic iron-deficient women, ferritin <50) overreaches the data.
In [1] iron improved the fatigue scale but not quality of life (p=0.2), depression or anxiety, suggesting the effect may be instrument-specific rather than a broad functional benefit.
Where it remains uncertain. The largest intravenous trial [2] found no significant overall effect (P=.07), with benefit confined to ferritin ≤15 (P=.005), and [6] was null on fatigue.
Aleatory
[8] reports iron corrected iron status with a highly variable individual response, and [4] notes variable improvement, so any single woman's fatigue change is uncertain.
Epistemic
[2] found no significant overall effect (P=.07); whether a real effect exists above ferritin 15 is unresolved and would need a larger adequately powered trial.
Inferential
Fatigue is measured by self-report scales across trials, exposing the outcome to expectation effects, especially where blinding is weaker.
The load-bearing papers from a corpus of 10, each classified by what it does to the claim. Every DOI is taken from the corpus the claim was graded on.
Largest direct RCT; significant between-group fatigue reduction in the exact population.
“The mean score on the Current and Past Psychological Scale for fatigue decreased by 47.7% in the iron group and by 28.8% in the placebo group (difference -18.9%, 95% CI -34.5 to -3.2; p=0.02)”
Panel auditInternal validity: high · scope of inference: Non-anaemic iron-deficient menstruating women aged 18-53 with unexplained fatigue in French primary care.Key limitations: closed-label (only observer-blinded) · no effect on QoL, depression or anxiety · subjective fatigue outcome
Direct RCT whose overall fatigue effect was non-significant — a key limiting counterweight.
“In patients with baseline serum ferritin ≤ 15 ng/mL, fatigue decreased by 1.8 in the iron group compared with 0.4 in the placebo group (P = .005)”
Panel auditInternal validity: high · scope of inference: Non-anaemic premenopausal women with fatigue and serum ferritin <=50 ng/mL; benefit concentrated in those with ferritin <=15 ng/mL.Key limitations: overall effect non-significant at P=.07 · efficacy bound to ferritin <=15 subgroup · subjective 0-10 fatigue scale
Third direct RCT reporting significant fatigue reduction, though as within-group change.
“In Group 1, significant decrease in fatigue score and significant increase in ferritin and haemoglobin levels were noted post-intervention (p=0.05).”
Panel auditInternal validity: medium · scope of inference: Non-anaemic iron-deficient women aged 18-45 at a single Lahore hospital.Key limitations: only within-group change reported, not iron-vs-placebo delta · p=0.05 borderline · single centre
3 of 10 papers shown. The full review lists all of them, with the panel’s arbitration →
Claims are graded at each quarterly release, and re-graded between releases only when a pivotal trial lands. Every change is a new version of the claim.
Consistent directional RCT evidence in the target population supports the claim, but a key overall-null trial and modest, subgroup-dependent effects cap confidence at Likely.
Release 2026-q4 re-graded every claim from its corpus under protocol v0.19. An earlier release's grade is shown for the record; it came from an earlier protocol and is not a movement.
Assumptions that carry weight but are not themselves established.
The panel records the gap that would most move the claim, and the study that would close it.
Adequately powered trial across ferritin <50. The best-controlled trial [2] was overall null and positive only at ferritin ≤15, so the effect across the wider claimed range is unestablished. The panel rates this the highest-importance open gap for the claim, and names the study design that would close it: A large double-blind placebo-controlled trial enrolling non-anaemic women across the full ferritin <50 range, pre-specifying analysis by baseline ferritin band.
Open question: Does iron reduce fatigue in non-anaemic women with ferritin between 15 and 50, or only below 15? Why it is still open: [2] was overall null (P=.07) with a significant effect confined to ferritin ≤15 (P=.005).
Priors is a sceptical first reader, not peer review, and not medical advice.
Release 2026-q4 · graded 18 Sep 2026 · protocol v0.19