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Fe9.0
Iron Research
Probably helpsModerate safety
43 peer-reviewed studies
What the evidence says
Likely helps
Iron appears to help in 10 of 14 studies with measurable effects — the evidence leans clearly favourable.
Most evidence is from high-quality meta-analyses and randomised trials published 2012–2026 with a typical study size of 529 participants.
Based on 43 studies · 18 meta-analyses · 10 RCTs · 545,585 total participants
Confidence
High
What the studies found
10helped2unclear2didn't help· 29 more without graded effect data
By outcome
Iron deficiency & anemia
Likely helps39 studies
Women's healthMay help reduce menstrual discomfort and PMS symptoms · 1-3 cycles · Provides essential nutrients for healthy pregnancy · Ongoing
Likely helps16 studies
Safety profile
Mostly mechanism / observational8 studies
Therapeutic & clinical
Mostly mechanism / observational6 studies
Energy & fatigueSignificant energy improvement if deficient · 2-4 weeks for symptoms; 3-6 months to replenish stores
Likely helps5 studies
Digestive health
Mostly mechanism / observational5 studies
Endurance & exercise performanceImproved endurance and recovery if deficient · 4-8 weeks · Restores VO2 max and endurance when deficient · 4-12 weeks
Mostly mechanism / observational4 studies
Cognitive function
Too few graded studies2 studies
Heart & blood pressure
Too few graded studies1 study
Kidney & renal health
Too few graded studies1 study
By the numbers
Pulled from 31 studies with measurable effects
Likely real effects
100%
across studies
People studied
546k
typical study: 529 people
Strongest designs
28
18 pooled, 10 randomised
Showed benefit
71%
10/14 studies
How long studies ran
1–4 weeks
1
1–3 months
3
Populations Studied
Adults2
Pregnant women1
Women1
Iron replete non-anemic pregnant women1
Active research area
34 studies in the last 5 years · Latest meta-analysis: 2025
201220192026
1Low birthweightMeta-AnalysisCited 22×n=48,971 · very large study2024
Daily oral iron supplementation during pregnancy may reduce maternal anaemia and iron deficiency at term.
Finkelstein JL et al. · The Cochrane database of systematic reviews (2024)
Noticeable benefit
← WorseNo effectBetter →
There is probably little to no difference in maternal death (2 versus 4 events, RR 0.57, 95% CI 0.12 to 2.69; 3 trials, 14,060 women; moderate-certainty evidence).
Infant outcomes: Women taking iron supplements are probably less likely to have infants with low birthweight (5.2% versus 6.1%; RR 0.84, 95% CI 0.72 to 0.99; 12 trials, 18,290 infants; moderate-certainty evidence), compared to placebo or no iron supplementation.
However, the evidence is very uncertain for infant birthweight (MD 24.9 g, 95% CI -125.81 to 175.60; 16 trials, 18,554 infants; very low-certainty evidence).
2Lung cancer riskMeta-AnalysisCited 8×n=21,943 · very large study2024
However, a positive association was observed between dietary heme iron and the risk of lung cancer in women, which may require further investigation.
Mohammadzadeh M et al. · International journal for vitamin and nutrition research. Internationale Zeitschrift fur Vitamin- und Ernahrungsforschung. Journal international de vitaminologie et de nutrition (2024)
Noticeable harm
← WorseNo effectBetter →
Methods: We searched PubMed, Web of Science, Scopus and Google scholar for eligible articles published through May 2023 reporting the Relative Risk (RR), Hazard Ratio (HR) or Odds Ratio (OR) with 95% confidence interval (95% CI).
There were no significant associations between the highest dietary total iron (heme and non-heme) (RR: 1.09, 95% CI: 0.78 to 1.51) or heme iron (RR: 1.01, 95% CI: 0.73 to 1.38) intake compared to the lowest intake with lung cancer risk.
However, in the subgroup of women (cases n=5074), heme iron was associated with a 14% increase in the risk of lung cancer (RR: 1.14, 95% CI: 1.01 to 1.29).
3Iron deficiency at termMeta-AnalysisCited 19×n=2,822 · very large study2023
Daily iron supplementation in iron replete non-anemic pregnant women probably reduces the risk of maternal iron deficiency anemia at term and low birthweight.
Hansen R et al. · Acta obstetricia et gynecologica Scandinavica (2023)
Large benefit
← WorseNo effectBetter →
In addition, it may reduce iron deficiency at term (RR: 0.74, 95% CI: 0.60-0.92; 4 RCTs, 1663 women; I2 = 58%; low-certainty evidence) and the incidence of small for gestational age babies (RR: 0.39, 95% CI: 0.17-0.86; 1 RCT, 213 infants; I2 not estimable; low-certainty evidence).
Daily iron supplementation in iron replete non-anemic pregnant women probably reduces the risk of maternal iron deficiency anemia at term and low birthweight.
4Hemoglobin levelsMeta-AnalysisCited 4×n=529 · large study2024
ALA supplementation had no statistically significant effect on iron-related parameters.
Sharifi-Zahabi E et al. · International journal for vitamin and nutrition research. Internationale Zeitschrift fur Vitamin- und Ernahrungsforschung. Journal international de vitaminologie et de nutrition (2024)
Noticeable benefit
← WorseNo effectBetter →
Likely real
In subgroup analysis, ALA significantly increased hemoglobin in patients with hematological disorders (WMD = 1.23 g/dL; 95% CI: 1.00, 1.45 g/dL; I2 = 96.6%, p < 0.001) and in studies with durations longer than 8 weeks (WMD = 1.03 g/dL; 95% CI: 0.82, 1.25 g/dL; I2 = 96.5%, p = 0.02).
ALA supplementation had no statistically significant effect on iron-related parameters.
5Anemia prevalenceMeta-AnalysisCited 19×n=722 · large study2024
It was found that dietary factors were one of the major causes of anemia, and iron-containing supplements and nutrition counseling could be effective interventions to reduce the prevalence of anemia, ID, and IDA among Chinese pregnant women.
Zhou Y et al. · Nutrients (2024)
No clear effect
← WorseNo effectBetter →
The results showed that the prevalence of anemia, ID, and IDA among pregnant women in China were 30.7% (95% CI: 26.6%, 34.7%), 45.6% (95% CI: 37.0%, 54.2%), and 17.3% (95% CI: 13.9%, 20.7%), respectively.
Generally, lower prevalence was observed in the economically more advanced eastern region of the country, while the prevalence of ID was higher in the eastern region than that in the western region.
The prevalence of anemia and IDA in rural areas was higher than that in urban areas, but ID prevalence was higher in urban areas.
6Fatigue reductionMeta-AnalysisCited 5×n=572 · large study2024
Intravenous iron probably reduces fatigue slightly in the early postpartum weeks (8 to 28 days) compared to oral iron tablets, but probably results in little to no difference after four weeks.
Jensen MCH et al. · The Cochrane database of systematic reviews (2024)
Noticeable benefit
← WorseNo effectBetter →
Likely real
Intravenous iron versus oral iron supplementation The evidence is very uncertain about the effect of intravenous iron on mortality (risk ratio (RR) 2.95, 95% confidence interval (CI) 0.12 to 71.96; P = 0.51; I² = not applicable; 3 RCTs; 1 event; 572 women; very low-certainty evidence).
Intravenous iron probably results in a slight reduction in fatigue within 8 to 28 days (standardised mean difference -0.25, 95% CI -0.42 to -0.07; P = 0.006; I² = 47%; 2 RCTs; 515 women; moderate-certainty evidence).
Oral iron probably increases the risk of constipation compared to intravenous iron (RR 0.12, 95% CI 0.06 to 0.21; P < 0.001; I² = 0%; 10 RCTs; 1798 women; moderate-certainty evidence).
7Sports performanceSystematic ReviewCited 12×n=669 · large study2024
Endurance performance improved by 2-20% in iron-deficient athletes with supplementation.
Burden RJ et al. · European Journal of Sport Science (2024)
Large benefit
← WorseNo effectBetter →
23 studies with 669 athletes analyzed
Iron deficiency reduces performance by 3-4%
100mg/day elemental iron effective for 56 days
8Meta-AnalysisCited 158×n=451,723 · very large study2020
In addition, they further contribute to the ongoing discourse of choosing antenatal MMN over IFA as the standard of care in LMICs.
Oh C et al. · Nutrients (2020)
IFA supplementation showed notable improvement in maternal anemia and the reduction in low birthweight, whereas LNS supplementation had no apparent effect on outcomes; further research that compares LNS and MMN supplementation could help understand differences with these commodities.
For single micronutrient supplementation, improvements were noted in only a few outcomes, mainly pre-eclampsia/eclampsia (calcium), maternal anemia (iron), preterm births (vitamin D), and maternal serum zinc concentration (zinc).
These findings highlight that micronutrient-specific supplementation should be tailored to specific groups or needs for maximum benefit.
9Haemoglobin concentrationMeta-AnalysisCited 125×n=8,506 · very large study2016
Daily iron supplementation effectively reduces the prevalence of anaemia and iron deficiency, raises haemoglobin and iron stores, improves exercise performance and reduces symptomatic fatigue.
Low MS et al. · The Cochrane database of systematic reviews (2016)
Noticeable benefit
← WorseNo effectBetter →
Women receiving iron had a higher haemoglobin concentration at the end of intervention compared to women receiving control (mean difference (MD) 5.30, 95% CI 4.14 to 6.45, 51 studies, 6861 women, high quality evidence).
Women receiving iron had a reduced risk of iron deficiency compared to women receiving control (RR 0.62, 95% CI 0.50 to 0.76, 7 studies, 1088 women, moderate quality evidence).
Seven trials recruiting 901 women reported on 'any side effect' and did not identify an overall increased prevalence of side effects from iron supplements (RR 2.14, 95% CI 0.94 to 4.86, low quality evidence).
11Gastrointestinal side-effectsMeta-AnalysisCited 516×n=3,168 · very large study2015
Our meta-analysis confirms that ferrous sulfate is associated with a significant increase in gastrointestinal-specific side-effects but does not find a relationship with dose.
Tolkien Z et al. · PloS one (2015)
Huge harm
← WorseNo effectBetter →
Likely real
Ferrous sulfate supplementation significantly increased risk of GI side-effects versus placebo with an odds ratio (OR) of 2.32 [95% CI 1.74-3.08, p<0.0001, I2 = 53.6%] and versus i.v. iron with an OR of 3.05 [95% CI 2.07-4.48, p<0.0001, I2 = 41.6%].
Subgroup analysis in IBD patients showed a similar effect versus i.v. iron (OR = 3.14, 95% CI 1.34-7.36, p = 0.008, I2 = 0%).
Likewise, subgroup analysis of pooled data from 7 RCTs in pregnant women (n = 1028) showed a statistically significant increased risk of GI side-effects for ferrous sulfate although there was marked heterogeneity in the data (OR = 3.33, 95% CI 1.19-9.28, p = 0.02, I2 = 66.1%).
12Hemoglobin levelsMeta-AnalysisCited 7×n=120 · medium study2024
There is moderate-quality evidence suggesting that probiotics, prebiotics, and synbiotics may improve anemia management, particularly by enhancing Hb levels.
Hu Q et al. · BMC gastroenterology (2024)
Noticeable benefit
← WorseNo effectBetter →
Likely real
The analysis revealed that probiotics, prebiotics, or synbiotics significantly improved Hb levels in patients with anemia (WMD = 10.760, 95% CI: 4.593 to 16.747, p = 0.001), though heterogeneity was high (I² = 96.5%).
Two RCTs (n = 120 participants) reported significant increases in serum iron levels in the probiotic group (WMD = 3.835, 95% CI: 3.271 to 4.400), with moderate heterogeneity (I² = 38.7%).
Two RCTs (n = 192 participants) reported no significant differences were observed between the groups in serum ferritin levels (WMD = 8.048, p = 0.115), and heterogeneity remained high (I² = 62.6%).
13Thyroid function parametersMeta-AnalysisCited 37×2023
Further studies are needed to understand the role played by iron in thyroid metabolism.
Garofalo V et al. · Nutrients (2023)
Likely real
Patients with ID showed TSH (MD: -0.24 mIU/L; 95% CI -0.41, -0.07; I2 = 100%, p = 0.005), FT4 (MD: -1.18 pmol/L; 95% CI -1.43, -0.94; I2 = 99%, p < 0.000001), and FT3 (MD: -0.22 pmol/L; 95% CI -0.32, -0.12; I2 = 99%, p < 0.00001) levels that were significantly lower.
Our systematic review of the literature found that ID significantly increases the prevalence of thyroid autoantibody (anti-thyroglobulin antibodies and anti-thyroid peroxidase antibodies) positivity both individually and collectively.
Conclusion: Studies currently published in the literature indicate a possible relationship between ID, thyroid function, and autoimmunity, especially in some patient groups.
14Allogeneic blood transfusionMeta-AnalysisCited 65×n=372 · medium study2019
The use of iron therapy for preoperative anaemia does not show a clinically significant reduction in the proportion of trial participants who received an allogeneic blood transfusion compared to no iron therapy.
Ng O et al. · The Cochrane database of systematic reviews (2019)
No clear effect
← WorseNo effectBetter →
The 372 participants in our analysis fall far short of the 819 required - as calculated by our information size calculation - to detect a 30% reduction in blood transfusions.
Meta-analysis of iron therapy versus placebo or standard care showed no difference in the proportion of participants who received a blood transfusion (risk ratio (RR) 1.21, 95% confidence interval (CI) 0.87 to 1.70; 4 studies, 200 participants; moderate-quality evidence).
There was no difference between the iron therapy and placebo/standard care groups for haemoglobin level preoperatively at the end of the intervention (mean difference (MD) 0.63 g/dL, 95% CI -0.07 to 1.34; 2 studies, 83 participants; low-quality evidence).
Ferrous bisglycinate shows some benefit over other iron supplements in increasing hemoglobin concentration and reducing GI adverse events among pregnant women.
Fischer JAJ et al. · Nutrition reviews (2023)
Ferrous bisglycinate shows some benefit over other iron supplements in increasing hemoglobin concentration and reducing GI adverse events among pregnant women.
More trials are needed to assess the efficacy of ferrous bisglycinate against other iron supplements in other populations.
16Serum ferritin levelsMeta-AnalysisCited 135×n=27 · very small study2018
In conclusion our results showed that vegetarians are more likely to have lower iron stores compared with non-vegetarians.
Haider LM et al. · Critical reviews in food science and nutrition (2018)
Noticeable benefit
← WorseNo effectBetter →
Likely real
The meta-analysis which combined data of 24 cross-sectional studies showed that adult vegetarians have significantly lower serum ferritin levels than their non-vegetarian controls (-29.71 µg/L, 95% CI [-39.69, -19.73], p < 0.01).
Inclusion of semi-vegetarian diets did not change the results considerably (-23.27 µg/L, 95% CI [-29.77, -16.76], p < 0.01).
The effects were more pronounced in men (-61.88 µg/L, 95% CI [-85.59, -38.17], p < 0.01) than in both premenopausal women (-17.70 μg/L, 95% CI [-29.80, -5.60], p < 0.01) and all women (-13.50 μg/L, 95% CI [-22.96, -4.04], p < 0.01), respectively.
17Iron-deficiency anemia diagnosis and treatmentSystematic ReviewCited 25×2020
These recommendations may serve as a starting point for clinicians to better diagnose and treat IDA in patients with gastrointestinal bleeding, which ultimately may improve health outcomes in these patients.
Cotter J et al. · World journal of gastroenterology (2020)
These recommendations may serve as a starting point for clinicians to better diagnose and treat IDA in patients with gastrointestinal bleeding, which ultimately may improve health outcomes in these patients.
19Muscle wasting and functional declineSystematic Review2026
Aging Cell published by Anatomical Society and John Wiley & Sons Ltd.
Zeidan RS et al. · Aging cell (2026)
We delineate key knowledge gaps, including the absence of ferroptosis-specific biomarkers in human muscle and limited longitudinal data linking ferroptotic stress to mobility outcomes.
Finally, we highlight potential therapeutic opportunities targeting iron handling and lipid peroxidation pathways.
A better understanding of the contribution of ferroptosis to muscle aging may enable development of mechanistically informed biomarkers and interventions to preserve strength and mobility in older adults.
20maternal haemoglobin before deliveryRCTn=1,206 · large study2026
Among non-anaemic iron deficient pregnant women, intravenous iron therapy significantly improved maternal haemoglobin before delivery, compared with oral iron prophylaxis.
Wasim T et al. · The Lancet. Haematology (2026)
Among non-anaemic iron deficient pregnant women, intravenous iron therapy significantly improved maternal haemoglobin before delivery, compared with oral iron prophylaxis.
Ferritin screening should be considered in early pregnancy, as intravenous iron therapy is effective in those tested positive for non-anaemic deficiency.