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Iron (ferritin-gated)

Bisglycinate, alternate-day

StrongLikely visible in your data
3
sources
3
trials
198
participants (largest study)
2
study designs
The verdict

In menstruating women with low ferritin (under 50 µg/L) but no anemia, iron cut fatigue by almost half versus a third on placebo. Iron deficiency also lowers VO₂ max and raises resting heart rate — so correcting a real deficiency is one of the most wearable-visible changes possible. But iron is only helpful when you are actually low, and harmful when you're not: test first.

Why this grade
Emerging
Preliminary or mechanistic
Moderate
Some RCTs, limited replication
Strong
Multiple RCTs or meta-analyses, consistent direction

Strong — conditional on a ferritin test. Two RCTs (CMAJ, BMJ) plus IV-iron trials agree; hemochromatosis (~1 in 250) makes blind supplementation unsafe.

How it works

Iron is needed for hemoglobin and mitochondrial enzymes; deficiency limits oxygen delivery and forces the heart to beat faster for the same output.

Who it helps, and who it doesn't

Menstruating women, endurance athletes, vegetarians — after ferritin + CBC. Alternate-day dosing improves absorption; take away from coffee, tea and calcium.

Measured effects (absolute, from the trials)

Every estimate, against a line of no effect

Diamonds are point estimates; the hairline is the 95% confidence interval where the trial reported one.

  • Fatigue score (iron)
    % · Vaucher 2012
    −47.7%
    [not reported]
  • Fatigue score (placebo)
    % · Vaucher 2012
    −28.8%
    [not reported]
−40%−20%0NO EFFECT

Units are never mixed on one line: each scale gets its own axis. Where a trial reported no confidence interval we leave it blank rather than inventing one.

Studies over time

3 studies across 14 years

2003 — 2017
20032007201020142017
Meta-analysis or systematic reviewRandomized or crossover trialObservational or preliminaryHover a marker for detail
Dose
60–100 mg elemental every other day + vitamin C (trial: 80 mg/day × 12 wk; alternate-day per absorption studies)
Timing
Away from coffee, tea and calcium
Safety flags
  • ⚑ Ferritin + CBC
  • · NEVER without ferritin + CBC — hemochromatosis affects ~1/250; excess iron is pro-oxidant.
Where to buyRecord what I'm taking

References

  1. 1.
    Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial
    CMAJ · 2012 · rct · n = 198

    80 mg/day for 12 weeks: fatigue −47.7% vs −28.8% placebo in women with ferritin <50 µg/L.

  2. 2.
    Iron supplementation for unexplained fatigue in non-anaemic women: double blind randomised placebo controlled trial
    BMJ · 2003 · rct · n = 144

    Fatigue improved with iron, mainly in women with ferritin ≤50 µg/L.

  3. 3.
    Iron absorption from oral iron supplements given on consecutive versus alternate days
    The Lancet Haematology · 2017 · crossover · n = 40

    Alternate-day dosing raised fractional iron absorption versus daily dosing.

Umbral is a wellness product, not a medical device. It does not diagnose, treat, cure or prevent any disease. Supplement information is educational; talk to a clinician before starting anything, especially if you are pregnant, under 18, managing a condition or taking medication.