Iron

Automated reading of the published studies (Decosa evidence engine), for outcomes Dr. Grey has not graded yet. It is not a Dr. Grey grade and does not change one. How it is read

• Endurance performance

  The best available review (2025, 23 studies, 669 people) found an improvement in endurance performance. That review studied high-level iron deficient female athletes. 4 of the 6 studies read agree; 1 found no clear difference, 1 found no clear answer. The evidence is moderate.

  6 studies counted of 8 read: 5 reviews and 1 trial (166 people in the trials).

  1. Systematic review, 2025; 23 studies, 669 people; high-level iron deficient female athletes: improves (the review the verdict rests on). Iron deficiency, supplementation, and sports performance in female athletes: A systematic reviewPubMed 39536912
  2. Systematic review, 2025; football players: improves. The efficacy of dietary supplements on health status and performance of football players: a systematic reviewPubMed 39915258
  3. Systematic review, 2018; 12 studies, 283 people; iron-deficient nonanemic athletes: unclear: evidence too weak to tell. Supplementing IDNA athletes with iron improved performance in 6 studies (146 participants) and did not … Does Iron Supplementation Improve Performance in Iron-Deficient Nonanemic Athletes?PubMed 29792778
  4. Meta-analysis, 2015; 17 studies; iron deficient non-anaemic endurance athletes: improves. moderate effect on improving [Hb] (Hedges' g=0.695, 95% CI 0.533 to 0.836, p<0.001) and (VO(2max)) … Is iron treatment beneficial in, iron-deficient but non-anaemic (IDNA) endurance athletes? A systematic review and meta-analysisPubMed 25361786
  5. Systematic review, 2007; 3 studies; children and adolescents: improves. Treadmill endurance time was significantly better in iron Effect of iron supplementation on physical performance in children and adolescents: systematic review of randomized controlled trialsPubMed 17277426
  6. Randomised trial, 1988; 166 people; female intercollegiate athletes and non-athletes: no clear difference. did not report a greater improvement in performance Iron deficiency in female athletes: its prevalence and impact on performancePubMed 3367745

  Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.

• Fatigue

  Mixed or unclear: two readings of the studies disagreed. One reading found mixed results for fatigue, the other an improvement. The question is open.

  Side effects: 2 of the 3 studies that reported on them found more with Iron (gastrointestinal side effects, constipation).

  7 studies counted of 11 read: 5 reviews and 2 trials (119 people in the trials).

  1. Meta-analysis, 2019; 11 studies, 1,074 people; adults with non-anaemic iron deficiency: unclear: evidence too weak to tell (the review the verdict rests on). Intravenous iron therapy for non-anaemic, iron-deficient adultsPubMed 31860749
  2. Meta-analysis, 2025; 18 studies, 1,408 people; non-anemic children, adolescents, and menstruating adults: improves. supplementation improved symptoms of anxiety (d = 0.34), fatigue (d = 0.34) Psychiatric and cognitive outcomes of iron supplementation in non-anemic children, adolescents, and menstruating adults: A meta-analysis and systematic reviewPubMed 40945632
  3. Meta-analysis, 2017; 6 studies; patients with iron deficiency without anaemia: improves. significant therapeutic effect of Fe in fatigue Iron deficiency without anaemia is a potential cause of fatigue: meta-analyses of randomised controlled trials and cross-sectional studiesPubMed 28625177
  4. Meta-analysis, 2016; 67 studies, 8,506 people; menstruating women: improves. Iron supplementation improved maximal and submaximal exercise performance, and appears to reduce symptomatic fatigue. Daily iron supplementation for improving anaemia, iron status and health in menstruating womenPubMed 27087396
  5. Meta-analysis, 2016; 21 studies; people with non-anaemic iron deficiency: improves. improvement in objective scores (P = 0.005) and self-rating (P = 0.03) of fatigue Non-anaemic iron deficiency - a disease looking for recognition of diagnosis: a systematic reviewPubMed 26256281
  6. Randomised trial, 2025; 26 people; iron-deficient recreationally active females of reproductive age: improves. Fatigue scores improved in IRON but not PLA Effect of intravenous iron therapy on exercise performance, fatigue scores and mood states in iron-deficient recreationally active females of reproductive age: a double-blind, randomised control trial (IRONWOMAN Trial)PubMed 40032294
  7. Randomised trial, 2023; 93 people; healthy non-anemic male and female athletes: improves. significant reduction in tired feeling/exhaustion after the exercise Influence of iron supplementation on fatigue, mood states and sweating profiles of healthy non-anemic athletes during a training exercise: A double-blind, randomized, placebo-controlled, parallel-group studyPubMed 36817736

  Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.

• Memory

  The best available review (2026, 17 studies) found an improvement in memory. That review studied children. 4 of the 7 studies read agree; 3 found no clear difference. The evidence is moderate.

  Possible harm: 1 study read reported a worse result for memory with Iron. One abstract says: "increasing iron correlated poorer memory and general cognitive performance in adulthood" Check the studies below, and ask a doctor or pharmacist if this applies to you.

  7 studies counted of 8 read: 5 reviews and 2 trials (94 people in the trials).

  1. Systematic review, 2026; 17 studies; children: improves (the review the verdict rests on). modest benefits in domains such as intelligence, memory Effect of iron supplements on cognitive development in children: an umbrella reviewPubMed 41710280
  2. Meta-analysis, 2025; 18 studies, 1,408 people; non-anemic children, adolescents, and menstruating adults: improves. In RCTs, supplementation improved symptoms of anxiety (d = 0.34), fatigue (d = 0.34), physical … Psychiatric and cognitive outcomes of iron supplementation in non-anemic children, adolescents, and menstruating adults: A meta-analysis and systematic reviewPubMed 40945632
  3. Systematic review, 2022; 50 studies; adolescents: no clear difference. iron supplementation did not improve memory and recall Iron Status, Anemia, and Iron Interventions and Their Associations with Cognitive and Academic Performance in Adolescents: A Systematic ReviewPubMed 35011099
  4. Systematic review, 2014; 11 studies; pre-menopausal women: improves. Increasing iron and zinc in pre-menopausal women and its effects on mood and cognition: a systematic reviewPubMed 25405366
  5. Meta-analysis, 2010; 14 studies; children aged 6+, adolescents, and women: no clear difference. had no effect on non-anaemic participants, or on memory The effects of oral iron supplementation on cognition in older children and adults: a systematic review and meta-analysisPubMed 20100340
  6. Randomised trial, 2025; 94 people; heart transplant recipients with iron deficiency: no clear difference. did not differ statistically significantly between study groups Cognitive Function Among Heart Transplant Recipients Before and After Intravenous Iron Supplement for Iron Deficiency: Results From a Randomized, Placebo-Controlled, Double-Blind Treatment TrialPubMed 41182019
  7. Randomised trial, 1986; young pregnant women aged 14-24: improves. significant improvement on the most sensitive measure of short-term memory A randomized trial of oral iron on tests of short-term memory and attention span in young pregnant womenPubMed 3511017

  Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.

• Stress

  Mixed or unclear: two readings of the studies disagreed. One reading found evidence too weak to tell for stress, the other a worse result. The question is open.

  Harm reported: the studies read found a worse result for stress with Iron. One abstract says: "Markers of oxidative stress were also significantly altered, with higher malondialdehyde (MDA: 3.9 ± 0.7 µmol/L vs. 2.4 ± 0.5 µmol/L)" Talk to a doctor or pharmacist before taking it for this.

  1 study counted of 9 read: 1 review.

  1. Meta-analysis, 2014; 34 studies, 2,658 people; hemodialysis patients with functional iron deficiency anemia: unclear: evidence too weak to tell (the review the verdict rests on). significant increases in plasma malonyldialdehyde level Efficacy and safety of intravenous iron therapy for functional iron deficiency anemia in hemodialysis patients: a meta-analysisPubMed 24513913

  Automated reading of the published studies (Decosa evidence engine), run 30 Sep 2026. It reads abstracts, can miss studies, and a repeat run can differ.