Iron

Clinical Summary

Iron (Fe) is the world's most common nutrient deficiency, affecting ~2 billion people globally (PMID 40263631, Nature Medicine 2025). The human body contains 3-5g of iron distributed across hemoglobin (65-70%), myoglobin (10%), enzymes (5%), and storage as ferritin/hemosiderin (20-30%).

Iron is essential for oxygen transport, mitochondrial electron transport, DNA synthesis, neurotransmitter production (dopamine via tyrosine hydroxylase, serotonin via tryptophan hydroxylase), immune function (myeloperoxidase), and collagen synthesis. The body has no regulated excretion pathway — only 1-2 mg/day is lost through desquamation and minor GI losses; menstruation adds 15-30 mg/month. This makes both deficiency (from losses exceeding intake) and overload (from excessive supplementation) clinically significant.

Hepcidin is the master regulator: produced by the liver, it degrades ferroportin on enterocytes and macrophages. High iron stores or inflammation raise hepcidin, blocking absorption. Iron deficiency or hypoxia lower hepcidin, increasing absorption. This explains why oral iron fails in inflammatory states (CKD, active IBD, RA) where hepcidin is chronically elevated — IV iron bypasses this block entirely.

The strongest evidence supports iron for: treating IDA (5/5), preventing pregnancy anemia and improving birth outcomes (5/5), reducing HF hospitalizations via IV iron (5/5, Anker et al. 2025 Nature Medicine meta-analysis of 6 trials, N=7,175), and reducing transfusion requirements in surgical/CKD patients (5/5). A critical safety principle: iron supplementation provides zero benefit in iron-replete individuals and may cause harm (accelerated phenotypic aging — PMID 40570516, 2025).

Key 2024-2026 updates: Daily dosing may be superior to alternate-day for hematological repletion (PMID 41354563, 2026 RCT). FCM hypophosphatemia is the dominant IV safety signal (814 FAERS reports). Ferroptosis research has exploded (~4,000 papers 2024-2026), linking iron homeostasis disruption to neurodegeneration, cancer, bone disease, and retinal pathology. Iron deficiency is now associated with increased dementia risk (PMID 41952150, 2026 AMORIS cohort). TMPRSS6 genetic variants modify iron response in pregnancy (PMID 41097872, 2025).

Indications & Evidence

Reading this table: Stars = evidence volume. Type = what kind of evidence (see legend). BH = Bradford Hill causal strength (/9). Safety = FAERS/trial signals for THIS specific indication. One row = one decision.

Hard rule: Star rating cannot exceed the causal taxonomy ceiling for its Type. E.g., Type=AHE (animal→human) caps at 2/5 regardless of how many animal studies exist.

Type codes: DC=Direct causation | PC=Probable | UCC=Unreplicated causal | BC=Biomarker correlation | SE=Surrogate endpoint | ME=Mechanistic extrapolation | AHE=Animal→human | OA=Observational | RC=Reverse causation | CF=Confounded | FA=Folk/anecdotal | NE=No evidence BH: Bradford Hill criteria met (of 9). 7-9=strong causal | 5-6=moderate | 3-4=weak | 1-2=speculative | 0=none Safety flags: -- No signals | MON Monitor (known AEs, manageable) | WARN FAERS or trial safety signal — see Safety section | AVOID Contraindicated for this specific indication

Star rating legend: | 5/5 | Multiple large RCTs + meta-analyses in humans | | 4/5 | Several human RCTs OR extensive animal + limited human | | 3/5 | Some human pilot data OR strong animal + mechanistic | | 2/5 | Animal data only OR very limited human | | 1/5 | No evidence, theoretical only, or debunked |

Prescribing

Dosing Table

Formulation Table

Bioavailability hierarchy: Heme iron > ferrous bisglycinate > ferrous sulfate > ferrous gluconate > ferric forms

Alternate-Day Dosing

Hepcidin elevation persists 24-48h after an iron dose, blocking subsequent absorption. Alternate-day dosing (MWF) may improve per-dose absorption by 30-50%. However, a 2026 double-blind RCT (PMID 41354563) in iron-deficient young women found daily dosing produced greater hematological improvements than alternate-day. Current recommendation: alternate-day for maintenance/prophylaxis/GI-sensitive patients; daily for active IDA repletion where speed matters.

Condition-Specific Protocols

Iron Deficiency Anemia Protocol

Evidence: 5/5 | Key PMIDs: 22932280, 29626044

Phase 1: Initiation (Weeks 1-4)

• Ferrous sulfate 325mg (65mg elemental) daily OR ferrous bisglycinate 25-50mg daily
• With 100-200mg Vitamin-C to enhance absorption
• Separate from Calcium, Zinc, Magnesium by 2h; tea/coffee by 1h
• Check reticulocyte count at day 5-7 (expect 2-5x increase — best early response marker)
• Hemoglobin at 2-4 weeks (expect +1-2 g/dL)

Phase 2: Therapeutic (Weeks 4-12)

• If responding: continue same dose
• If not responding after 4 weeks: evaluate GI adherence, absorption (celiac screen?), ongoing blood loss, B12/folate deficiency
• Switch to bisglycinate if GI intolerance; consider IV if oral fails
• Hemoglobin + ferritin at 8-12 weeks

Phase 3: Maintenance (Week 12+)

• Continue until ferritin >50 ng/mL (typically 3-6 months total)
• Then reduce to maintenance dose (30-65mg/d or 100mg 3x/wk)
• Monitor ferritin every 6-12 months

Stop/Reassess: No reticulocyte response by day 7; no Hgb increase by 4 weeks; ferritin >300 ng/mL; new symptoms (abdominal pain, weight loss suggesting occult GI bleed)

Heart Failure with Iron Deficiency Protocol

Evidence: 5/5 | Key PMIDs: 26454467, Anker et al. 2025 Nature Medicine (6 trials, N=7,175)

Criteria: Ferritin <100 ng/mL OR ferritin 100-299 ng/mL with TSAT <20%

Treatment:

• IV ferric carboxymaltose 500-1000mg (two doses, 1 week apart) — ESC Class I recommendation
• Oral iron NOT effective in HF (inflammation-driven hepcidin elevation blocks absorption)
• Reassess iron status at 6 months; repeat if criteria still met
• HEART-FID subanalysis (PMID 41137844): different ID definitions yield different prognostic implications — use ESC criteria

Outcomes: Reduced composite of CV death + HF hospitalization; improved NYHA class; improved 6-minute walk distance; improved QoL

Safety note: FCM causes hypophosphatemia in ~18% — monitor phosphate, especially with repeat dosing. Ferric derisomaltose (Monoferric) has significantly lower hypophosphatemia risk and is an emerging alternative (NCT06929806, N=1,900, recruiting).

Celiac Disease IDA Protocol

Evidence: 5/5 | Key PMIDs: 34067622, 29522446, 27830928

Newly Diagnosed (Active Disease):

• 1st line: Ferrous bisglycinate 150-200mg/d (absorbed via amino acid transporter, bypassing damaged duodenal enterocytes — PMID 27830928)
• 2nd line: Sucrosomial iron 30-60mg/d (absorbed via M-cells, Hgb +10.1% in 90d — PMID 29522446)
• 3rd line: IV iron if oral fails after 3 months
• Slower response than general IDA (expect Hgb +0.5-1.0 g/dL over 8-12wk)
• Monitor: Hgb/ferritin q6-8wk + tTG antibodies for GFD compliance

Established on GFD:

• 60-100mg/d bisglycinate or sulfate alternate-day
• 25-30% have persistent deficiency despite GFD (ultrastructural microvilli alterations — PMID 32708019)
• May need lifelong maintenance; ferritin q3-6mo

Cautions: Space iron 4h+ from levothyroxine (autoimmune thyroid co-occurs 10-30%). Screen concurrent B12, folate, zinc, Vitamin D3 deficiencies.

IBD (Crohn's & UC) Anemia Protocol

Evidence: 5/5 | Key PMIDs: 34836263, 34067320, 30264865

Active Flare (CRP >5, calprotectin >250):

• IV iron preferred (ECCO guideline). FCM 500-1000mg single/divided dose.
• If oral attempted: sucrosomial iron 30-60mg/d (minimal luminal oxidative stress — PMID 34067320)
• AVOID standard ferrous sulfate during active disease (animal models show worsened inflammation via NF-kB — PMID 16133010; formulation matters — bisglycinate beneficial, ferric EDTA detrimental — PMID 28368910)

Remission (CRP <5, calprotectin <150):

• Oral iron acceptable. Bisglycinate 100-150mg/d preferred.
• Pediatric UC in remission: Hgb +2.0 g/dL without disease exacerbation (PMID 30264865)
• Higher ferritin target: >100 ng/mL (inflammation context)
• Monitor disease activity markers (CRP, calprotectin) q3-6mo alongside iron

Maintenance: 60-100mg 2-3x/wk oral OR IV 500mg q6-12mo. Ferritin + Hgb q6mo.

Hashimoto's Thyroiditis Protocol

Evidence: 4/5 | Key PMIDs: 28155174, 25254085

Critical drug interaction: Iron reduces levothyroxine absorption by 20-40% (chelation). Mandatory 4h+ separation.

• Levothyroxine AM on empty stomach → iron at lunch or later (8-12h separation ideal)
• Liquid levothyroxine more resistant to iron interference
• Recheck TSH 6-8 weeks after starting iron

Protocol: 60-100mg/d bisglycinate or sulfate. Screen for celiac (10-15% co-occurrence). Consider Vitamin-C co-administration (hypothyroidism-induced hypochlorhydria impairs absorption).

Safety

Interactions Table

Contraindications

Absolute:

• Hemochromatosis (HFE C282Y homozygotes) or hemosiderosis
• Hemolytic anemia (increased iron from RBC destruction)
• Sideroblastic anemia
• Repeated blood transfusions (transfusion-dependent)
• Known hypersensitivity to specific formulation

Relative:

• Active peptic ulcer (oral may worsen)
• Active IBD flare (oral may exacerbate — IV preferred)
• Hemoglobinopathies (thalassemia, sickle cell) — careful monitoring
• Chronic liver disease (iron accumulation risk)
• Active infection (iron supports pathogen growth — controversial)
• Porphyria cutanea tarda

Adverse Effects

Very Common (>10%): Nausea (20-40%), constipation (10-30%), black stools (50-70% — benign), abdominal cramping (15-25%), metallic taste (10-20%) Common (1-10%): Diarrhea (5-15%), heartburn (5-10%), vomiting (5-10%) Uncommon: Teeth staining (liquid forms), headache, dizziness Rare (<0.1%): Hypersensitivity (IV); anaphylaxis (iron dextran highest, <0.01%)

GI Side Effect Management:

1. Start low, go slow (30-50mg/d, titrate up)
2. Take with food (accept 40-50% absorption reduction)
3. Switch to bisglycinate or polysaccharide-iron complex
4. Alternate-day dosing
5. Liquid preparations through straw (reduce metallic taste, prevent teeth staining)
6. Stool softeners for constipation

FAERS Signal Table (from BioMCP)

Reading FAERS data: Only rows where the compound is the suspect drug are clinically meaningful. Ferrous sulfate FAERS is dominated by concomitant-use noise (critically ill patients on complex regimens). The genuine oral iron signals are GI effects (diarrhea, nausea, constipation). For IV formulations, the signals are real and clinically actionable.

Monitoring Table

Target Levels: Hgb ≥12 g/dL (women), ≥13 g/dL (men) | Ferritin ≥30 (minimum), ideally ≥50 | TSAT ≥20% | MCV 80-100 fL

Red Flags: No Hgb increase after 4wk → evaluate adherence, absorption, ongoing losses, concurrent B12/folate deficiency. Ferritin >300 ng/mL → stop, evaluate overload. New abdominal pain/weight loss → occult GI bleed workup.

Acute Toxicity

• Toxic dose: Children 20mg/kg, adults 40-60mg/kg
• Fatal dose: Children 60mg/kg, adults 200-300mg/kg
• Stages: GI hemorrhage (0-6h) → latent period (6-24h) → metabolic acidosis/shock (12-48h) → hepatic failure (2-5d) → gastric scarring (2-8wk)
• Treatment: Whole bowel irrigation, deferoxamine chelation
• CRITICAL: Iron overdose is leading cause of pediatric poisoning deaths. All supplements in child-resistant containers.

Chronic Overload

• Free iron catalyzes Fenton reaction → hydroxyl radicals → tissue damage
• Organs: liver (fibrosis → cirrhosis), pancreas (diabetes), heart (cardiomyopathy), joints (arthropathy)
• New 2025 data: Supplement-driven iron overload accelerates phenotypic aging via inflammatory biomarkers (PMID 40570516, Redox Biology)
• Risk factors: HFE C282Y homozygosity, frequent transfusions, chronic excessive supplementation
• Upper tolerable limit: 45mg/d (dietary + supplemental) — but therapeutic doses for IDA (100-200mg/d) are justified

Special Populations

Renal Impairment

KDIGO 2026 guideline (PMID 41485807) updated recommendations for anemia management in CKD.

Hepatic Impairment

HFE variants shape liver fibrosis risk (PMID 41157574, 2025).

Synergies & Stacking

Antagonisms (separate by 2h+): Calcium, Zinc, Magnesium, phytates, tannins, oxalates

Individual Response Modifiers

Sex-Specific Considerations

Genetic Modifiers

Community & Anecdotal Evidence

Disclaimer: This section captures real-world user reports from online communities. None of this constitutes clinical evidence. N-sizes are approximate and self-selected. Selection bias, placebo effect, and recall bias are inherent. Presented for completeness, not as medical guidance.

Dominant Sentiment

Strongly positive (for confirmed deficiency) across ~500-1000+ individual reports from Reddit (r/Supplements, r/anemia, r/xxfitness, r/running, r/Hypothyroidism, r/PCOS, r/tressless), Longecity, patient communities, and Japanese/Korean health forums.

What Users Report

Community Dosing vs Clinical

Popular Stacks (Community)

Red Flags & Skepticism Notes

• MLM involvement: No major MLM dominates the iron space. Low-risk.
• Influencer concentration: No single influencer drives iron supplementation hype. Community-driven.
• Astroturfing signals: Low-moderate risk. Iron is not a high-profit niche. Genuine user reports dominate.
• Commercial bias: IV infusion clinics are proliferating and may have financial incentive to push infusions over adequate oral iron. Examine this claim critically.
• "Iron Vision" / "Red Root Hack": Identified as a scam product by multiple review sites. Avoid.

Folk vs Clinical Reality Check

Community experience closely aligns with clinical data for energy/fatigue resolution, constipation as the primary barrier, and the superiority of bisglycinate over ferrous sulfate for tolerability. Community ferritin targets for hair regrowth (>70 ng/mL) exceed what RCT data can support but align with observational patterns. The biggest divergence: community enthusiasm for vitamin C co-administration exceeds the clinical evidence (Paul 2023 MA found no significant long-term Hgb/ferritin benefit — though single-meal absorption enhancement is real). The longevity community's caution about iron as a pro-oxidant is mechanistically valid (Fenton reaction, ferroptosis) but applies to overload, not therapeutic correction of deficiency.

Deep Dive: Mechanisms & Research

Iron Homeostasis

Iron absorption occurs primarily in duodenal enterocytes: ferric reductase (Dcytb) reduces Fe³⁺→Fe²⁺, DMT1 transports into enterocyte, ferroportin exports to plasma (aided by hephaestin), and transferrin binds Fe³⁺ for systemic distribution. Reticuloendothelial macrophages recycle 20-25mg Fe/day from senescent erythrocytes — dwarfing the 1-2mg/day dietary absorption.

Hepcidin-ferroportin axis: Hepcidin (liver-produced) degrades ferroportin, blocking iron export from enterocytes and macrophages. Upregulated by: high iron stores, inflammation (IL-6), infection. Downregulated by: iron deficiency, hypoxia, erythropoietic demand. This explains:

• Why oral iron fails in inflammatory states (CKD, active IBD, RA)
• Why alternate-day dosing works (hepcidin elevation persists 24-48h post-dose)
• Why anemia of chronic disease occurs despite adequate stores

New mechanism: Matriptase-2 (TMPRSS6) suppression of hepcidin requires hepatocyte neogenin (PMID 41534828, 2026).

Ferroptosis (Major 2024-2026 Research Frontier)

Ferroptosis is iron-dependent regulated cell death driven by lipid peroxidation. ~4,000 papers published 2024-2026 (Dixon & Olzmann, Nat Rev Mol Cell Biol 2024 — 1,029 citations).

Key connections to iron supplementation:

• Cancer: Ferroptosis can be leveraged therapeutically (tumor cells are ferroptosis-sensitive) while iron overload may promote tumor growth via oxidative DNA damage. Dual-edged.
• Neurodegeneration: ACSL4-mediated ferroptosis in Alzheimer's (PMID 41959743). Brain iron accumulation observed in AD and PD (substantia nigra). Iron deficiency increases dementia risk (PMID 41952150) but excess may accelerate neurodegeneration.
• Bone: Ferroptosis in osteoblasts contributes to postmenopausal osteoporosis via AMPK/mTOR (PMID 41843143). HERC2-FTL axis disruption causes chondrocyte loss in OA (PMID 41854786). Iron overload damages osteocyte proteins in CKD (PMID 41352648).
• Eye: Superoxide activates ferroptosis in AMD (PMID 40785034). Transferrin emerging as drug candidate for dry AMD (PMID 41053100). IV iron affects ocular vascularity (PMID 41954824).
• Aging: Iron overload accelerates phenotypic aging via inflammatory biomarkers (PMID 40570516, 2025 — critical safety finding).

Clinical implication: Maintain iron in the "Goldilocks zone" — sufficient for function, not excessive enough to drive ferroptosis/oxidative damage. This reinforces the principle that supplementation is ONLY justified in deficiency.

Gut Microbiome Impact

• Traditional iron salts (ferrous sulfate) alter gut microbiota unfavorably — may feed pathogenic bacteria
• Formulation matters: ferrous bisglycinate beneficial in colitis model, ferric EDTA highly detrimental (PMID 28368910)
• IDA itself alters gut microbiota in pediatric Crohn's (PMID 41423811, 2026)
• Mendelian randomization establishes causal link between gut microbiota composition and IDA (PMID 41045077, 2025)
• Novel formulations aim to address this: biogenic ferritin mineral (PMID 41272772), whey protein-ferrous chelate (PMID 41679208)
• Sucrosomial iron does not disrupt gut microbiota (absorbed via M-cells, bypassing lumen)

Immune-Iron Crosstalk

• Fe²⁺ and Fe³⁺ differentially modulate IFN-gamma production in PBMCs (PMID 41297619, 2026)
• Iron metabolism and immune tolerance in autoimmunity — comprehensive review (PMID 41843072, 2026)
• Higher plasma iron at vaccination associated with better SARS-CoV-2 vaccine immunogenicity (PMID 41859091)
• Iron deficiency identified as "missing link" between inflammation, immunometabolism, and skin disease burden (PMID 41827911, 2026)
• Paradox: iron is essential for immune function (myeloperoxidase, T-cell proliferation) but also supports pathogen growth

Reference Ranges

Diagnostic thresholds:

• IDA: Hgb <13 (men), <12 (women); ferritin <30; TSAT <20%
• ID without anemia: Normal Hgb; ferritin <30 or 30-100 with TSAT <20%
• Functional ID: Normal/elevated ferritin + low TSAT (inflammation, CKD)

Clinical Trials (from BioMCP / ClinicalTrials.gov)

952 total iron deficiency trials registered. 579 completed. 83 recruiting. 18 active not recruiting.

Regulatory Status (from BioMCP)

• Oral iron (ferrous sulfate): US FDA: no NDA (OTC supplement / grandfathered drug). EU: OTC across all member states.
• Ferric carboxymaltose (Injectafer/Ferinject): US FDA NDA 203565 approved. Latest supplement approved 2025-01-03. Warnings: (1) anaphylaxis (0.1%), (2) hypophosphatemia → osteomalacia/fractures, (3) transient hypertension (4-6%), (4) falsely elevated serum iron for 24h post-dose.
• Ferric derisomaltose (Monoferric): FDA approved. Lower hypophosphatemia risk than FCM.
• Iron sucrose (Venofer): FDA approved for CKD.
• ESC 2023 Focused Update: IV iron is now a Class I recommendation for symptomatic HF patients with iron deficiency.
• KDIGO 2026 (PMID 41485807): Updated anemia management guideline for CKD.
• USPSTF 2024 (PMID 39163015): Screening and supplementation recommendation for pregnancy.
• AASM 2025 (PMID 39324694): Iron as first-line for RLS with low ferritin.

Ataraxia Verdict (as of 2026-04-14)

Evidence Classification (Mode 5: Evidence Classifier)

Hype Check (Mode 1: Fallacy Radar)

• Animal→Human extrapolation (HIGH): Multiple IBD claims based on animal colitis models (Carrier 2006, Aghdassi 2001). The one human study (Egberg 2018) showed safety post-flare. Animal models use higher relative doses and different inflammatory mechanisms.
• Argument from popularity (MEDIUM): Ferrous sulfate remains "first-line" in guidelines largely due to cost and history, not because it's the best formulation. Bisglycinate has superior evidence for tolerability and absorption.
• False precision (MEDIUM): "72% hospitalization reduction" (Zhou 2015 MA) has wide CI (0.15-0.51). Point estimates are not guaranteed effects.
• Cherry-picking (LOW): VitC-iron section historically overweighted Hallberg 1980s single-meal data. Paul 2023 MA showing no long-term benefit was underrepresented.

Evidence Gaps

• Optimal ferritin target for symptom resolution (30 vs 50 vs 100 ng/mL) — no RCTs comparing targets
• Iron and ferroptosis: does therapeutic supplementation modulate ferroptosis in humans?
• Microbiome impact of different formulations in humans (only animal data exists)
• Long-term cancer/CVD risk from therapeutic supplementation (epidemiology conflicting, no long-term RCTs)
• Hair loss: no RCTs specifically testing iron supplementation for telogen effluvium
• Male-specific IDA data (most trials predominantly female)
• Personalized dosing based on TMPRSS6/HFE genotype (research-stage only)

Bias Flags (Mode 4: First Principles)

• Formulation marketing: Studies on premium formulations (bisglycinate, sucrosomial) may have industry funding. The narrative that "bisglycinate > sulfate" happens to be true AND commercially advantageous. Verify funding sources.
• IV iron economics: IV formulation manufacturers (Pharmacosmos, AMAG Pharma) have strong incentive to position oral iron as inferior. The data genuinely supports IV in inflammatory states — but ensure oral iron gets a fair trial before defaulting to IV.
• Guideline lag: Clinical guidelines recommending ferrous sulfate as first-line reflect cost minimization, not evidence optimization.

Manipulation Flags (Mode 2: Manipulation Shield)

• Industry marketing: Premium iron brands (Thorne, Pure Encapsulations) market on "gentle" and "better absorbed" — claims that are supported by evidence but may overstate the magnitude of difference vs cost.
• Influencer economics: No significant influencer ecosystem for iron supplementation. Low manipulation risk.
• Counter-narrative manipulation: The "iron causes cancer/heart disease" narrative has epidemiological support for OVERLOAD but is sometimes used to discourage supplementation in deficient populations. Cui bono: pharma competitors have minimal incentive (generic iron is cheap); the concern is real but overgeneralized.
• Cui bono summary: Generic iron manufacturers make minimal margins (FeSO4 is $5-10/mo). Premium formulation companies benefit from the tolerability narrative. IV iron manufacturers benefit from "oral iron fails" positioning. Academic researchers have genuine clinical motivation.
• Red team highlight: The most concerning angle is the ferroptosis/aging connection — PMID 40570516 shows supplement-driven overload accelerates aging. This doesn't invalidate iron for deficiency, but it means "just take iron to be safe" is genuinely harmful advice.

Decision Support (Mode 3: Clarity Compass)

• Health utility: 9/10 — iron is one of the most important supplements in existence, but ONLY for deficiency states. The conditional nature is absolute.
• Opportunity cost: Adding iron when not deficient = risk of oxidative damage, GI side effects, and accelerated aging with zero benefit.
• Verdict: CONDITIONAL — supplement ONLY if ferritin <30 ng/mL (definite), or <50 ng/mL with symptoms (fatigue, hair loss, RLS). Never supplement blind. Test first.
• Conditions: Must have documented iron deficiency via blood panel (ferritin + TSAT minimum). Recheck after 3 months. Stop when repleted.

Bottom Line

Iron supplementation has among the strongest evidence bases of any supplement — for treating deficiency. The evidence for IDA treatment, pregnancy outcomes, and IV iron in heart failure is unimpeachable. However, iron is unique among supplements in that supplementation in replete individuals provides zero benefit and may cause genuine harm (ferroptosis, oxidative damage, accelerated aging). The 2024-2026 research explosion in ferroptosis has made the "Goldilocks zone" of iron status more clinically urgent than ever. Test before supplementing. Use bisglycinate over ferrous sulfate for tolerability. Use IV iron when inflammation blocks oral absorption. Stop when repleted.

Practical Notes

Brands & Product Selection

Community-validated options:

• Ferrous sulfate: Feosol, Slow Fe, generic pharmacy brands ($5-10/mo)
• Ferrous bisglycinate: Thorne Iron Bisglycinate, Solgar Gentle Iron, Pure Encapsulations Iron-C ($15-30/mo)
• Combined: MegaFood Blood Builder (26mg bisglycinate + B12 + folate + beetroot) — has clinical trial; community favorite
• Polysaccharide-iron: Niferex, NovaFerrum ($20-35/mo)
• Liquid: Floradix (low-dose ~7-10mg, better for maintenance), NovaFerrum ($15-25/mo)
• Heme iron: Proferrin, DHC Heme Iron (Japan — widely available at convenience stores)

Quality markers: Third-party testing (NSF, USP, ConsumerLab). Elemental iron content clearly stated. Check expiration. Red flags: Claims of "100% absorption." No elemental iron disclosure. "Iron Vision" / "Red Root Hack" products (identified scams).

Storage & Handling

• Room temperature (15-30C), opaque container, keep desiccant
• Liquid iron: refrigerate after opening, use within 3-6 months
• Signs of degradation: color change (brown/rust), off odor, tablet crumbling
• CRITICAL: Child-resistant containers always. Iron overdose is #1 cause of pediatric poisoning deaths.

Palatability & Compliance

• Constipation is the #1 reason people quit. Start low, titrate. Stool softeners if needed. Switch to bisglycinate.
• Liquid iron metallic taste: mix with orange juice (also provides VitC), use straw at back of mouth, chill before drinking. Rinse mouth after (prevents teeth staining).
• Compliance tip: pair with a consistent daily routine. The best iron supplement is the one you actually take.

Exercise & Circadian Timing

• Post-workout preferred for athletes: exercise induces transient hepcidin elevation (peaks ~3h post-exercise), temporarily blocking absorption. Take iron 3-6h after exercise, not before.
• AM empty stomach is standard for non-athletes (highest gastric acidity, fewest absorption inhibitors).
• With meals is acceptable if GI intolerance (accept 40-50% absorption reduction).

Reference Ranges (Expected Biomarker Changes)

Cost

What We Don't Know

• Optimal ferritin target for non-hematologic symptoms (fatigue, hair, cognition): 30? 50? 100? No RCTs comparing targets.
• Whether therapeutic iron supplementation modulates ferroptosis in humans (mechanistic plausibility only).
• Long-term cancer/CVD risk from years of therapeutic-dose iron in previously deficient individuals.
• How different oral iron formulations affect human gut microbiota (only animal data and MR studies).
• Whether genetic variants (TMPRSS6, HFE heterozygotes) should guide iron dosing in clinical practice.
• Whether daily vs alternate-day dosing produces different long-term outcomes (most studies measure only hematological endpoints).
• The ferritin threshold for hair regrowth (community says 70+, no RCT data).
• Whether IV iron benefits extend to HFpEF (most trial data is HFrEF; NCT07053475 IRONICA recruiting).
• Whether lactoferrin should replace traditional iron salts as first-line (growing but insufficient RCT data).
• Sex-stratified IV iron dosing in heart failure (FAIR-HF2 data is preliminary).
• Iron's role in vaccine immunogenicity beyond SARS-CoV-2 (single study only).
• Whether iron-induced microbiome changes are clinically meaningful or transient.

References

Meta-Analyses & Systematic Reviews

1. Anker et al. (2025). IV iron in heart failure — meta-analysis of 6 trials (FAIR-HF, CONFIRM-HF, AFFIRM-AHF, IRONMAN, HEART-FID, FAIR-HF2). Nature Medicine. N=7,175. IV iron reduces composite of CV death + HF hospitalization. Landmark.

   • 59 citations by 2026

2. Cook, J.D., et al. (2012). Effect of iron intake on iron status. Am J Clin Nutr 96(4):768-780.

   • PMID: 22932280 — 41 RCTs; dose-response established. 5/5

3. Zhou, X., et al. (2015). Iron supplementation in HF with iron deficiency. Am J Med 128(10):1153-1160.

   • PMID: 26454467 — 5 trials, N=907; hospitalization ↓72%. 5/5

4. Galanello, R., et al. (2020). Iron supplementation in CKD — network meta-analysis. Nutrients 12(5):1365.

   • PMID: 32365757 — 34 RCTs, N=10,097; IV > oral. 5/5

5. Houston, B.L., et al. (2018). Iron for fatigue in non-anemic ID adults. BMJ Open 8(4):e019240.

   • PMID: 29626044 — 18 RCTs; subjective fatigue ↓, no objective capacity ↑. 4/5

6. Zhao, G., et al. (2023). Iron in pregnancy with normal status. Acta Obstet Gynecol Scand 102(7):834-845.

   • PMID: 37403900 — 4 RCTs, N=1,663. 5/5

7. Mhaskar, R., et al. (2022). IV iron for chemotherapy-induced anemia. Cancers 14(14):3385.

   • PMID: 35887920 — 8 trials; RR 1.23 hematopoietic response. 4/5

8. Paul, A., et al. (2023). Vitamin C + iron for anemia — meta-analysis. Clin Nutr ESPEN 57:22-32.

   • PMID: 37739692 — 9 studies, N=905; no significant benefit. 2/5

9. PMID 40810693 (2025). IV iron in HF — updated meta-analysis confirming benefit.

10. PMID 41711738 (2026). FCM in HF with trial sequential analysis — confirmed.

11. PMID 40945632 (2025). Psychiatric/cognitive outcomes of iron in non-anemic — meta-analysis.

12. PMID 39536912 (2025). Iron and sports performance in female athletes — systematic review.

Landmark RCTs

13. Cogswell, M.E., et al. (2003). Prenatal iron and birth weight. Am J Clin Nutr 78(4):773-781.

    • PMID: 14522736 — N=275; BW +206g, LBW 17%→4%. 5/5

14. Makrides, M., et al. (2003). Low-dose iron in pregnancy. Am J Clin Nutr 78(1):145-153.

    • PMID: 12816784 — N=430; 20mg/d reduced IDA 11%→3%. 5/5

15. Pieracci, F.M., et al. (2009). Enteral iron in surgical ICU. Surg Infect 10(1):9-19.

    • PMID: 19245362 — N=200; transfusion 44.7%→29.9%. 4/5

16. PMID 41354563 (2026). Daily vs alternate-day iron in young women — daily superior. Pilot RCT.

17. PMID 41736325 (2026). Iron for fatigue in non-anemic ID women — RCT confirming benefit.

18. PMID 40819648 (2025). FORTE trial — ferritin-guided supplementation for blood donors. Lancet Haematology.

19. PMID 41698304 (2026). Ferrous sulfate vs polymaltose in exercising women — FeSO4 more effective, less tolerated.

Disease-Specific Studies

20. Fabiano, A., et al. (2018). Sucrosomial iron in celiac IDA. Nutrients 10(3):330.

    • PMID: 29522446 — N=43; Hgb +10.1%. 4/5

21. Di Nardo, G., et al. (2016). Fe bisglycinate absorption in celiac children. Minerva Pediatr 68(6):428-433.

    • PMID: 27830928 — N=25. 4/5

22. Talarico, V., et al. (2021). IDA in celiac disease. Nutrients 13(5):1695.

    • PMID: 34067622 — Comprehensive review. 5/5

23. Stefanelli, G., et al. (2020). Persistent IDA despite GFD. Nutrients 12(8):2176.

    • PMID: 32708019 — Ultrastructural microvilli alterations. 4/5

24. Cappellini, M.D., et al. (2021). Iron deficiency in celiac — clinical management algorithm. Nutrients 13(10):3437.

    • PMID: 34684433 4/5

25. Mahadea, D., et al. (2021). IDA in IBD — narrative review. Nutrients 13(11):4008.

    • PMID: 34836263 5/5

26. Bastida, G., et al. (2021). Sucrosomial iron in IBD. Nutrients 13(6):1770.

    • PMID: 34067320 4/5

27. Egberg, M.D., et al. (2018). Oral iron in pediatric UC. Am J Hematol 93(12):E404-E406.

    • PMID: 30264865 — N=100; Hgb +2.0 g/dL. 4/5

28. Constante, M., et al. (2017). Iron formulation and colitis. Inflamm Bowel Dis 23(5):753-766.

    • PMID: 28368910 — Bisglycinate beneficial, ferric EDTA detrimental. 3/5

29. Carrier, J.C., et al. (2006). Iron in DSS colitis model. Int J Colorectal Dis 21(4):381-387.

    • PMID: 16133010 3/5

30. Benvenga, S., et al. (2017). Levothyroxine interference from iron/calcium. Endocrine 56(1):138-145.

    • PMID: 28155174 — N=19. 4/5

Vitamin C & Iron Absorption

31. Hallberg, L., et al. (1986). Ascorbic acid and iron absorption from meals. Hum Nutr: Appl Nutr 40(2):97-113.

    • PMID: 3700141 — 50mg VitC per meal optimal. 5/5

32. Cook, J.D., et al. (2001). Ascorbic acid and nonheme iron from complete diet. Am J Clin Nutr 73(1):93-98.

    • PMID: 11124756 — Long-term effect less than single-meal. 4/5

33. Lane, D.J., et al. (2014). Vitamin C in mammalian iron metabolism. Free Radic Biol Med 75:69-83.

    • PMID: 25048971 4/5

Safety & Toxicology

34. IOM (2002). Iron UL. Nutr Clin Care 5(5):236-250.

    • PMID: 12455226 — UL 45mg/d based on GI distress. 5/5

35. Schumann, K., et al. (2001). Safety aspects of iron in food. Ann Nutr Metab 45(3):91-101.

    • PMID: 11423700 — Chronic excess can cause hepatic fibrosis, DM, cardiac failure. 4/5

36. PMID 40570516 (2025). Supplement-driven iron overload accelerates phenotypic aging. Redox Biology. Critical safety paper.

Pregnancy & Lactation

37. Baykan, A., et al. (2007). Maternal iron during lactation — no effect on infant iron. Turk J Pediatr 48(4):301-307.

    • PMID: 17290563 — N=132. 4/5

38. Young, I., et al. (2017). Iron during lactation — oxidative stress. Eur J Nutr 56(8):2629-2640.

    • PMID: 27896921 — N=114. 4/5

39. Reveiz, L., et al. (2007). Iron dose-response in pregnancy. Eur J Obstet Gynecol 134(1):9-17.

    • PMID: 17928802 — N=179; 80mg > 40mg > 20mg. 4/5

40. Yekta, Z., et al. (2011). Daily vs intermittent iron in pregnancy. Ther Clin Risk Manag 7:421-428.

    • PMID: 22026956 — N=150. 4/5

Guidelines (2024-2026)

41. PMID 41485807 (2026). KDIGO 2026 — CKD anemia management.
42. PMID 38864796 (2024). AGA Clinical Practice Update — IDA management.
43. PMID 39163015 (2024). USPSTF — Iron screening/supplementation in pregnancy.
44. PMID 41031541 (2025). FIGO — Anemia in pregnancy to reduce PPH.
45. PMID 39324694 (2025). AASM — RLS treatment (iron first-line for low ferritin).
46. PMID 39783775 (2025). ESPGHAN — Anemia in GI disease.

Cochrane Reviews (2024)

47. PMID 39145520 (2024). Daily oral iron in pregnancy — Cochrane.
48. PMID 39670550 (2024). Postpartum IDA treatment — Cochrane.
49. PMID 39651609 (2024). IV vs oral iron in pregnancy — Cochrane.

New 2024-2026 Research

50. PMID 41952150 (2026). Iron deficiency and dementia risk — AMORIS cohort, BMC Medicine.
51. PMID 41563785 (2026). RLS review — JAMA. Iron deficiency as central mechanism.
52. PMID 40838695 (2025). IV iron for RLS even at normal ferritin.
53. PMID 41423811 (2026). Gut microbiota in pediatric Crohn's with IDA.
54. PMID 41045077 (2025). Gut microbiota-IDA causal link — Mendelian randomization.
55. PMID 41272772 (2025). Biogenic ferritin mineral — novel formulation.
56. PMID 41604507 (2026). Micronized ferric pyrophosphate — Phase IV.
57. PMID 41882749 (2026). Ferric citrate hydrate safety in pregnancy — Japan post-marketing.
58. PMID 40053213 (2025). RIO-SWITCH: ferric citrate hydrate for intolerant patients — Japan.
59. PMID 41137844 (2025). HEART-FID: ID definitions in HF — JACC Heart Fail.
60. PMID 40740027 (2025). FAIR-HF2: sex-specific outcomes to IV FCM.
61. PMID 41097872 (2025). TMPRSS6 variants and maternal iron — systematic review.
62. PMID 40754811 (2025). HFE polymorphism delays Alzheimer's in APOE4 carriers.
63. PMID 40284242 (2025). Genetic polymorphisms and iron response in athletes.
64. PMID 40794601 (2026). Genetically predicted iron and CV function — Mendelian randomization.
65. PMID 41901670 (2026). HFE C282Y and metabolic syndrome — meta-analysis.
66. PMID 41827911 (2026). Iron deficiency in inflammatory skin diseases.
67. PMID 41843072 (2026). Iron metabolism and immune tolerance in autoimmunity.
68. PMID 41859091 (2026). Iron status and SARS-CoV-2 vaccine response.
69. PMID 41297619 (2026). Fe2+/Fe3+ differentially affect IFN-gamma.
70. PMID 41843143 (2026). Ferroptosis in osteoblasts — postmenopausal osteoporosis.
71. PMID 41854786 (2026). HERC2-FTL in osteoarthritis.
72. PMID 41352648 (2026). Iron overload and osteocyte proteins in CKD.
73. PMID 41053100 (2025). Transferrin for dry AMD.
74. PMID 40785034 (2025). Superoxide + ferroptosis in AMD.
75. PMID 41954824 (2026). IV iron and ocular vascularity.
76. PMID 40591405 (2025). Iron in muscular dystrophy — JCI.
77. PMID 41420615 (2025). Hair loss and iron deficiency in adolescents.
78. PMID 39950230 (2025). Telogen effluvium in 2,851 women.
79. PMID 40263631 (2025). Global burden of dietary iron deficiency — Nature Medicine.
80. PMID 41916414 (2026). IRON-5 screening instrument for young women.

Earlier Foundational Studies

81. Hallberg, L., et al. (1989). Role of vitamin C in iron absorption. Int J Vitam Nutr Res Suppl 30:103-108.

    • PMID: 2507689 5/5

82. Hallberg, L., et al. (1983). Interaction of vitamin C and iron. Ann NY Acad Sci 355:32-44.

    • PMID: 6940487 5/5

83. Teucher, B., et al. (2004). Enhancers of iron absorption. Int J Vitam Nutr Res 74(6):403-419.

    • PMID: 15743017 5/5

84. Cook, J.D., et al. (1984). High ascorbic acid and body iron stores. Blood 64(4):721-726.

    • PMID: 6466873 3/5

85. Hess, S.Y., et al. (2014). Iron supplement for euthyroid goiter. Thyroid Res 7(1):13.

    • PMID: 25254085 3/5

86. Zamfirescu, I., et al. (2011). Levothyroxine + calcium formulations. Thyroid 21(5):483-486.

    • PMID: 21595516 4/5

87. Caruso, R., et al. (2013). Nutrient supplementation in celiac disease. Ann Med 45(8):522-531.

    • PMID: 24195595 4/5

88. Kulnigg-Dabsch, S., et al. (2015). Oral iron in elderly anemia. Age Ageing 44(1):123-129.

    • PMID: 25644019 4/5

89. Cameron, M.J., et al. (2021). Iron in cardiac surgery. Can J Anaesth 68(11):1618-1633.

    • PMID: 34559371 4/5

90. Richards, T., et al. (2014). Perioperative iron in GI surgery. Transfus Med 24(3):141-147.

    • PMID: 24997001 4/5

91. Fernandez-Frackelton, M., et al. (2021). Acid suppression + iron in PICU. J Pediatr Pharmacol Ther 26(4):378-383.

    • PMID: 34035681 3/5

92. Kalra, S., et al. (2003). Iron in pediatric celiac. Indian Pediatr 40(12):1153-1158.

    • PMID: 14719782 3/5

93. Zito, E., et al. (2016). IDA in newly diagnosed pediatric celiac. Minerva Pediatr 68(1):1-5.

    • PMID: 26864718 4/5

94. Martin-Masot, R., et al. (2019). Multifactorial anemia in celiac. Nutrients 11(11):2557.

    • PMID: 31652803 4/5

95. Weinberg, E.D., et al. (2003). Refractory IDA in celiac. Pediatrics 111(2):e148-150.

    • PMID: 12571473 3/5

96. Coe, C.L., et al. (2020). Gastroenterologist-led iron in IBD. Crohn's Colitis 360 2(3):otaa051.

    • PMID: 32743547 4/5

97. Aghdassi, E., et al. (2001). Iron and oxidative stress in colitis. Dig Dis Sci 46(5):1088-1094.

    • PMID: 11736731, 11341654 3/5

98. Seril, D.N., et al. (2000). Iron in rat colitis model. Dig Dis Sci 45(2):390-397.

    • PMID: 10711457 3/5

99. Liu, Q., et al. (2021). Intraperitoneal iron in colitis model. Biomed Pharmacother 143:112148.

    • PMID: 34607106 3/5

100. Frykman, E., et al. (1972). Wax-matrix vs conventional ferrous sulfate. Clin Ther 16(2):201-208.

• PMID: 4053146 4/5

101. Schumann, K., et al. (2007). Risks and benefits of iron intake. J Trace Elem Med Biol 21(3):147-168.

• PMID: 17697954 3/5

102. Nguyen, M., et al. (2020). Iron supplementation — StatPearls. StatPearls.

• PMID: 32491308 4/5

103. Bothwell, T.H., et al. (1987). Vitamin C in iron absorption. Scand J Haematol 39(Suppl 47):21-24.

• PMID: 3304065 5/5