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Iron (Various Forms)
Essential mineral for oxygen transport and energy production — critical for those with deficiency, especially women and athletes.
What the evidence says
Iron appears to help in 5 of 7 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 1966–2026 with a typical study size of 2,822 participants.
Based on 814 studies · 135 meta-analyses · 608 RCTs · 3,436,483 total participants
Confidence
High confidenceWhat the studies found
By outcome
Numerous high-quality meta-analyses and RCTs show iron reliably corrects anemia, raises hemoglobin/ferritin, reduces fatigue and improves performance in deficient people; the only limits are GI side effects and harm if taken without deficiency.
650 randomised trials
86% were about Iron in an audit of 50 of them
Every randomised or controlled trial of Iron indexed in PubMed, not a hand-picked subset. Meta-analyses and systematic reviews are deliberately excluded from this count: most of them cover many compounds at once, so counting them would inflate it.
PubMed · as of Sep 2026
356 trials ongoing or recruiting · NaN completed on ClinicalTrials.gov
271 of the completed trials have posted results
Registered trials show research momentum for Iron, not proof of effect — a registration is a plan, and posted results are sponsor-reported, not peer-reviewed. They are never counted toward the evidence rating above.
Browse these trials on ClinicalTrials.govClinicalTrials.gov · as of Oct 2026
Under EU law (Reg. 1924/2006), EFSA reviews whether a specific health claim for Iron meets the evidence standard. These are independent regulatory decisions on claims — not studies, and never counted toward the evidence score above.
Authorised claims
“Iron contributes to normal cognitive function”
“Iron contributes to normal energy-yielding metabolism”
“Iron contributes to normal formation of red blood cells and haemoglobin”
“Iron contributes to normal oxygen transport in the body”
“Iron contributes to the normal function of the immune system”
“Iron contributes to the reduction of tiredness and fatigue”
“Iron has a role in the process of cell division”
Not authorised by EFSA
“Iron affects activity of heart, liver and muscles”
“Not authorised” means the specific claim wording did not meet the EU’s evidence standard — often a matter of dossier or phrasing, not proof of no effect. EFSA judges marketing claims and is kept separate from our study-based evidence score.
Source: EU Register of nutrition and health claims (European Commission / EFSA) · register snapshot Feb 2013
Iron is essential for hemoglobin production, oxygen transport, and cellular energy. Deficiency is the most common nutritional deficiency worldwide, affecting energy, cognition, immunity, and exercise performance. Different forms vary greatly in absorption and tolerability.
Only supplement if deficient or at risk — excess iron causes oxidative damage.
Essential component of hemoglobin
Required for mitochondrial function
How Iron works — from molecular targets to health outcomes. Click an edge to see supporting research.This visualization is in beta — pathways are being refined and expanded.
Higher needs (27mg/day); follow prenatal guidance
Lower risk of deficiency — test before supplementing
Iron can reduce oral levothyroxine absorption. Follow the exact thyroid product’s timing and order rather than a universal interval for all thyroid medicines.
Reduce iron absorption
Iron reduces antibiotic absorption. Each antibiotic's label sets its own gap, so ask the pharmacist to schedule iron apart from it.
Reduced levodopa effectiveness, worsening Parkinson symptoms
Significantly reduced antibiotic effectiveness
Reduced drug effectiveness for osteoporosis
Up to 90% reduction in antibiotic absorption
Antibiotic treatment failure
Counteracts therapeutic effect of iron chelation
Tip: Use bisglycinate form; add magnesium; increase fiber/water
Tip: Take with food; switch to gentler form
Tip: Iron can make stool darker. New black, tarry/sticky stool, visible blood, or uncertainty about possible bleeding needs urgent assessment now even without other symptoms. Vomiting blood, substantial ongoing bleeding, fainting/collapse or severe illness needs emergency help: call your local emergency number, 112 in the EU.
Iron has an evidence score of 9/10 — very strong evidence based on 821 indexed studies, including 17 meta-analyses. Essential mineral for oxygen transport and energy production — critical for those with deficiency, especially women and athletes. Representative study: PMID 39145520.
The commonly studied dose of Iron is 18-40mg elemental iron for deficiency (varies by severity) (a typical label dose, not the dose used in the cited trials, which used 60 to 120 mg a day). Individual needs vary — start at the lower end of the range and adjust based on how you respond.
The best time to take Iron is between meals. It can be taken on an empty stomach. Iron absorption is tightly regulated by hepcidin and occurs primarily in the duodenum via DMT1 (non-heme) and HCP1 (heme) transporters.
Iron has a safety rating of "moderate". That is a category, not a measure of individual risk, and there are precautions worth knowing. The most commonly reported side effects are constipation, nausea/GI upset, dark stools. Use caution if any of these apply to you: Hemochromatosis or iron overload; Repeated blood transfusions; Adequate iron stores (test first!).
Zinc
Likely helpsInvolved in 300+ enzymatic reactions — supports immune defense, testosterone production, wound healing, and sleep quality.
Electrolyte Complex
Too few graded studiesEssential minerals (sodium, potassium, magnesium) that drive hydration, rehydration, and neuromuscular function — most useful when sweat, illness, or low-carb diets deplete fluid and salt.
Caffeine
Probably helpsBlocks adenosine receptors to boost alertness, reaction time, and endurance — an umbrella review of 21 meta-analyses found it ergogenic for endurance, strength and power.
Vitamin D3
Probably helpsHormone-like vitamin that regulates 1,000+ genes — deficiency is widespread and linked to poor immunity, depression, and bone loss.
Supplements on GLP-1 Drugs
On Ozempic/Wegovy/Mounjaro? What actually helps — muscle preservation, GI relief, nutrient gaps (no upsell).
Supplements for Energy & Fatigue
Tired? Why most "energy" pills only work if they fix a deficit — and how to find yours first.
Thyroid Support
Selenium helps; iodine can WORSEN Hashimoto’s. The honest take on "thyroid support".
Supplements While Breastfeeding
What’s safe while nursing, the truth about milk-supply herbs, and what to avoid (it passes into milk).
Supplement Timing & Combining
When to take what, with or without food, and which supplements compete vs pair well.
Hair Loss: What Actually Works
The proven options (minoxidil, finasteride) vs adjuncts and weak naturals — tiered for pattern hair loss.
Supplements in Pregnancy
Commonly recommended vs ask-your-clinician vs avoid — a general, safety-first overview.
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Reviewed by Dr. Baher Al Hakim · Last reviewed May 2026 · evidence from 816 studies · how we score · editorial policy
This information is for educational purposes only. It is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting, stopping, or changing any supplement or medication.
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