Iron: why the number on the label is not the number your body gets

Iron is the nutrient where the gap between what you eat and what you absorb is widest. It is also the one where the same intake can be too little for one person and too much for another.

What it does in the body

• Iron is the part of haemoglobin that carries oxygen from the lungs to the tissues. Evidence E source

How much you need

• The RDA for iron is 8 mg a day for adult men, 18 mg for women aged 19–50, 8 mg for women 51 and over, and 27 mg in pregnancy. — adults Evidence E source
• People on vegetarian diets need 1.8 times as much iron as people who eat animal products. — vegetarians Evidence E source
• The Tolerable Upper Intake Level for iron is 45 mg a day for adults. — adults 14+ Evidence E source

How well your body absorbs it

• Iron absorption is about 14–18% from mixed diets containing meat, seafood and vitamin C, but only 5–12% from vegetarian diets. — adults Evidence E source
• Vitamin C, meat, poultry and seafood improve absorption of non-heme iron, while phytate in grains and beans and polyphenols in plant foods reduce it. Evidence E source
• Unlike other inhibitors, calcium can reduce absorption of both non-heme and heme iron. Evidence E source
• Plant foods and iron-fortified foods contain only nonheme iron, which is less bioavailable than the heme iron in meat, seafood and poultry. Evidence E source
• Spinach is named by NIH ODS as an example of a plant food that is a good source of iron by content but has low iron bioavailability because it contains absorption inhibitors such as polyphenols. Evidence E source
• Vegetarians really do carry less iron in store: their ferritin runs about 30 micrograms per litre lower, and the gap is largest in men. — adult vegetarians and semi-vegetarians against non-vegetarian controls Evidence C source
• Eating vitamin-C-rich fruit with a meal raised ferritin and haemoglobin a little, yet left measured iron absorption unchanged. — females aged 15 to 74 and children Evidence A source
• Tested head to head over eight weeks, beef did no more for iron status than plant-based meat: the famous 'meat factor' added nothing. — non-pregnant females of reproductive age, mean age 24, with serum ferritin below 25 micrograms per litre Evidence B source
• Heme iron, the form said to be absorbed several times better, cured anaemia in infants no faster than ordinary ferrous sulfate at the same dose. — anaemic infants aged 6 to 12 months in the Gambia, haemoglobin 7.0 to under 11.0 g/dL, adherence about 90 per cent Evidence B source
• Sourdough raises iron out of bread in the two hours after you eat it, and over twelve weeks that did not turn into more iron in the body, with ferritin actually falling in one trial. — healthy or iron-deficient adults and children in 8 human intervention studies, 1970 to December 2024 Evidence A source
• Taking the phytate out of bread only paid off in the long run when there was extra iron in the bread to take up. — healthy and iron-deficient participants in 8 intervention studies Evidence A source
• In the two-hour window after a meal the phytate story is real and large: low-phytate white bread doubled the serum iron rise compared with high-phytate wholemeal. — human volunteers in postprandial bioavailability studies Evidence C source
• Whether the iron in your diet is available is decided mostly by bread: in a national survey, bread and cereals were the biggest source of the phytate that blocks it. — participants of the Turkey Nutrition and Health Survey in 2010 and 2017 Evidence C source
• Phytate intake is moving, not fixed: in one country it rose by about a fifth in seven years, which quietly changes how much of the same iron gets absorbed. — the Turkish general population in 2010 and 2017 Evidence C source

What too little does

• Iron deficiency anaemia causes weakness, fatigue, difficulty concentrating and impaired immune function and work performance. — people with iron deficiency anaemia Evidence E source
• Iron deficiency anaemia in infancy can cause cognitive and psychological effects, some of which might be irreversible. — infants Evidence E source
• The line between anaemic and not moved in 2024, and it moved for exactly one group: children aged 6 to 23 months. — all population groups for whom WHO sets haemoglobin cutoffs Evidence E source
• Redrawing that line is not a technicality: in one Peruvian sample the share of young children counted as anaemic dropped from 62% to 47% overnight, with nothing about the children changing. — 310 children aged 6-59 months in Puno, Peru, recruited by convenience sampling at routine check-ups Evidence C source
• Anaemia is not a synonym for iron shortage: in these children inflammation explained more of it than iron did, 45.9% against 27.5%. — 310 children aged 6-59 months in Puno, Peru Evidence C source

What the evidence does and does not show

• A Cochrane review found daily supplementation with 9–90 mg of iron reduced the risk of anaemia at term in pregnant women by 70% and iron deficiency at term by 57%. — pregnant women Evidence A source
• The same review found daily iron supplements in pregnancy were associated with an 8.4% risk of a low-birthweight newborn against 10.2% without supplementation, and a mean birthweight 31 g higher. — pregnant women Evidence A source
• The US Preventive Services Task Force concluded the evidence is insufficient to weigh the benefits and harms of screening pregnant women for iron deficiency or routinely supplementing them with iron. — pregnant women Evidence A source
• In adults who are iron deficient but not anaemic, iron reduced self-reported fatigue but did not improve any objective measure of physical capacity. — adults aged 18 and over who were iron deficient without anaemia; 18 unique trials, 4 reporting fatigue and 9 reporting maximal oxygen consumption Evidence A source
• Taking iron every other day instead of every day gave haemoglobin gains that were statistically indistinguishable, with the same overall rate of side effects. — people with iron deficiency anaemia in the general population, excluding the pregnancy-specific literature; 11 randomised trials Evidence A source
• In the Cochrane review of 57 trials in 48,971 pregnant women, daily iron cut anaemia from 7.4 per cent to 4.0 per cent. — pregnant women in 14 of the 57 trials for this outcome Evidence A source
• Babies of women taking iron were slightly less likely to be born small, 5.2 per cent against 6.1 per cent. — infants in 12 trials Evidence A source
• In women who were not anaemic to begin with, 23 studies in 4,492 women found iron halved the risk of becoming anaemic, with ten women treated for one case prevented. — non-anaemic pregnant women, 23 studies Evidence A source
• Taking iron on alternate days instead of daily left slightly lower haemoglobin, caused far fewer stomach side effects and was taken more reliably. — pregnant women in low and middle income countries, 22 trials Evidence A source
• Cooking in an iron pot works about half the time, which is another way of saying nobody can tell you it will work for you: 4 of 8 pot studies and 1 of 3 ingot studies found a real change. — children aged 4 months to 11 years and females of reproductive age aged 12-51 in low- and middle-income countries Evidence A source
• The reason iron pots underperform is usually not chemistry but the kitchen: daily use of a pot ran as low as 27%, against 90% or more for an ingot dropped in the pan. — children and women of reproductive age in low- and middle-income countries Evidence A source
• Whether an iron pot helps depends on who is cooking in it and how often, not on the pot: the review's own explanation for the scatter is population and compliance. — children and females of reproductive age in low- and middle-income countries Evidence A source
• Most iron-pot studies did not record the two things most likely to cause the anaemia they were treating: malaria and intestinal worms. — the 11 included iron-cookware studies Evidence A source
• The iron fish, the cooking gadget that went round the world as a cheap cure for anaemia, changed nothing in the trial built to test it, and neither did iron tablets. — 340 rural Cambodian women aged 18-49 with mild or moderate anaemia; at baseline only 9% were iron deficient by ferritin, and structural haemoglobin variants were common Evidence B source
• The trialists' own recommendation names the condition under which the iron fish is the wrong answer: where iron deficiency is uncommon and inherited blood disorders are not. — rural Cambodian women with anaemia largely unrelated to iron Evidence B source

What too much does

• Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6. — children under 6 Evidence E source
• A single intake above 20 mg per kg of body weight, about 1,365 mg for a 150-pound person, can cause corrosive damage to the intestine, shock and organ failure. — adults and children Evidence E source
• High-dose iron supplements commonly cause gastric upset, constipation, nausea, abdominal pain, vomiting and diarrhoea. — people taking high-dose iron Evidence E source
• In hereditary hemochromatosis, untreated iron overload typically produces signs of toxicity by a person's thirties, including liver cirrhosis and heart disease. — people with HFE hemochromatosis Evidence E source
• Ferrous sulfate roughly doubles the odds of stomach trouble against placebo, and triples them against the same iron given by drip. — adults taking ferrous sulfate, the standard oral iron salt; 20 trials with a placebo arm and 23 with an intravenous iron arm Evidence A source
• Where malaria is common and untreated, iron supplements given to children raise malaria cases by about 15 per cent. Where prevention and treatment exist, they slightly lower them. — children in malaria-endemic areas, 19 trials analysed in this grouping Evidence A source

Medicines it interacts with

• Iron supplements can reduce the effectiveness of levothyroxine, and labels advise not taking them within 4 hours of each other. — people taking levothyroxine Evidence E source

What to do with this

The single most useful thing on this page is that iron is not a nutrient to self-prescribe.

Tiredness has many causes and iron deficiency is only one of them. A blood test tells you which, and it also catches the opposite problem, because iron overload does its damage quietly for years. Starting tablets on a hunch can be wrong in either direction.

What you can do without any test is change how much of your food's iron reaches you. Put vitamin C in the same meal as beans, lentils or fortified grains. Keep tea, coffee and a large dose of calcium for an hour later. If you eat no meat or fish, plan for needing more of it rather than the same amount.

Expect less from the individual tricks than the internet promises. Heme iron cured anaemia in infants no faster than ordinary ferrous sulfate. Beef did no more for iron stores over eight weeks than plant-based meat. Vitamin C rich fruit lifted ferritin and haemoglobin a little and left measured absorption unchanged. What is solid is the direction: vegetarians carry about 30 micrograms per litre less ferritin, so planning for more iron is sensible, and the plan is a whole diet rather than one clever pairing.

If you are already on tablets and they make you miserable, say so rather than stopping quietly. Ferrous sulfate roughly doubles the odds of stomach trouble against placebo, and across 43 trials the size of the dose made no difference to that. Alternate-day dosing is worth asking about, though outside pregnancy the trials counted the same rate of side effects either way.

And if there is a child in the house, the tablets go somewhere they cannot be reached.

Two popular shortcuts deserve less faith than they get. Cooking in an iron pot raised haemoglobin or iron measures in four of eight trials, and an iron ingot in one of three. The reviewers blamed the scatter on how often people actually used the thing, and daily use of a pot ran as low as 27 per cent against 90 per cent for an ingot. The iron fish, the version that travelled the world, was then tested properly in 340 anaemic Cambodian women and finished the year at the same haemoglobin as tablets and as nothing.

Phytate is the other one. Taking it out of bread doubles the rise in blood iron over the next two hours, and over twelve weeks on low-phytate sourdough rye ferritin fell from 32 to 27 micrograms per litre. Where the trick did pay off long-term, there was added iron in the bread to take up. Soak and sprout and leaven because it makes grains easier to digest, and do not count on it to fill an empty store.

Where to get it from food

The bottom line

Two things matter more than the milligram total: the form the iron comes in, and what you eat alongside it. Tea, coffee and calcium at the same meal get in the way, and that half is solid. Vitamin C is the famous fix, and trials that added vitamin C rich fruit to meals raised ferritin and haemoglobin a little while leaving measured absorption where it was, so treat it as a nudge rather than a lever. Supplementing without a blood test goes wrong in both directions, because iron deficiency needs treating and iron overload damages the liver and heart quietly for years. Pregnancy is the one setting with a large trial base behind it. A Cochrane review of 57 trials in 48,971 women found daily iron cut anaemia from 7.4 per cent to 4.0 per cent, and it barely moved preterm birth. One more thing belongs at the end, because it changes what a diagnosis means. Anaemia and iron shortage are two separate findings that happen to share a blood test. In 310 young children in Puno, Peru, iron deficiency explained 27.5 per cent of the anaemia and inflammation explained 45.9 per cent. The threshold that decides the label moved in 2024 as well. WHO changed the haemoglobin cutoff for children aged 6 to 23 months, and recalculating that Peruvian sample took the share counted as anaemic from 62 to 47 per cent. Nothing about the children changed.

Sources

1. iron-01 · Position of an expert body · expert body statement
   Iron is an essential component of hemoglobin, an erythrocyte (red blood cell) protein that transfers oxygen from the lungs to the tissues.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · extracted
2. iron-02 · Position of an expert body · expert body recommendation
   Men 19+: 8 mg; Women 19–50: 18 mg; Women 51+: 8 mg; Pregnancy: 27 mg (value from the source's table, not a sentence)
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
3. iron-03 · Position of an expert body · expert body recommendation
   The requirement for iron is 1.8 times higher for people who follow vegetarian diets than those for people who include animal products in their diet.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
4. iron-09 · Position of an expert body · expert body recommendation
   The ULs apply to healthy infants, children, and adults with a limit of 45 mg for adults ages 14–50+. (value from the source's table, not a sentence)
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
5. iron-04 · Position of an expert body · expert body statement
   The bioavailability of iron is approximately 14% to 18% from mixed diets that include substantial amounts of meat, seafood, and vitamin C (ascorbic acid, which enhances the bioavailability of nonheme iron) and 5% to 12% from vegetarian diets.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
6. iron-05 · Position of an expert body · expert body statement
   In addition to ascorbic acid, meat, poultry, and seafood can enhance nonheme iron absorption, whereas phytate (which is present in grains and beans) and certain polyphenols in some nonanimal foods (e.g., cereals, legumes) have the opposite effect.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · extracted
7. iron-06 · Position of an expert body · expert body statement
   Unlike other inhibitors of iron absorption, calcium might reduce the bioavailability of both nonheme and heme iron.
   NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
8. iron-18 · Position of an expert body · expert body statement
   Plants and iron-fortified foods contain nonheme iron only, whereas meat, seafood, and poultry contain both heme and nonheme iron. Heme iron has higher bioavailability than nonheme iron, and other dietary components have less effect on the bioavailability of heme than nonheme iron.
   NIH Office of Dietary Supplements, Iron - Health Professional Fact Sheet · checked 2026-09-16 · extracted
9. iron-19 · Position of an expert body · expert body statement
   Some plant-based foods that are good sources of iron, such as spinach, have low iron bioavailability because they contain iron-absorption inhibitors, such as polyphenols.
   NIH Office of Dietary Supplements, Iron - Health Professional Fact Sheet · checked 2026-09-16 · extracted
10. iron-n1 · Observational data · systematic review and meta-analysis of cross-sectional studies
    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)...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.
    Haider et al., Critical Reviews in Food Science and Nutrition, 2018 · checked 2026-09-17 · independently re-checked
11. iron-n2 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised trials
    Including ascorbate-rich fruits in meals had a positive impact on serum ferritin [7 trials, n = 762; mean difference (MD) = 9.39 μg/L; P < 0.001; moderate certainty], hemoglobin (12 trials, n = 1141; MD = 1.34 g/L; P = 0.01; moderate certainty), serum transferrin receptor (6 studies; MD = -0.37 mg/L; P < 0.001; high certainty), and iron balance (1 trial; MD = 2.4; low certainty)...No impact on iron absorption (3 studies; MD = 3.36%; P = 0.07, low certainty), plasma ferritin (4 studies; MD = -0.11 μg/L, P = 0.82; high certainty), or plasma transferrin receptor (3 studies; MD = 1.53 mg/L; very low certainty).
    American Journal of Clinical Nutrition, 2026 · checked 2026-09-17 · independently re-checked
12. iron-n3 · Randomised controlled trial(s) · randomised double-blind controlled trial
    Daily consumption of an iron supplement with a lunch meal for 8 wk improved serum ferritin concentrations (main time effect: +10.7 ± 9.6 μg/L, P < 0.0001), transferrin saturation (main time effect: +5.1% ± 18.7%, P = 0.048), soluble transferrin receptor (main time effect: -0.6 ± 1.0 mg/L, P < 0.001), body iron stores (main time effect: +2.8 ± 3.1 mg/kg, P < 0.0001), and hemoglobin (main time effect: +0.5 ± 0.9 g/dL, P = 0.0002) regardless of whether the meals contained Animal or Plant (treatment-by-time interaction: P > 0.05 for all indicators).
    American Journal of Clinical Nutrition, 2025 · checked 2026-09-17 · independently re-checked
13. iron-n5 · Randomised controlled trial(s) · randomised controlled trial
    The primary end points of hemoglobin and ferritin concentrations both improved by day 84 with no difference between treatments. For the secondary end point of anemia, the prevalence went from 83.7% to 46.2% in the ferrous sulfate group and from 84.6% to 47.1% in the HIP group. Infants who received HIP had higher serum iron concentration (by 48.4%; 95% CI: 15.4%, 91.0%)
    American Journal of Clinical Nutrition, 2025 · checked 2026-09-17 · independently re-checked
14. iron-e1-07 · Meta-analysis or systematic review · systematic review of human intervention studies
    On the other hand, long-term human intervention trials indicate that these improvements do not necessarily favor iron status under free-living conditions and may even lead to reductions in serum ferritin and total body iron.
    Frontiers in Nutrition, 2026 · checked 2026-09-18 · independently re-checked
15. iron-e1-08 · Meta-analysis or systematic review · systematic review of human intervention studies
    Importantly, the more promising results (in the long-term) were mainly observed when phytate reduction was combined with iron fortification protocols or with iron-rich vehicles.
    Frontiers in Nutrition, 2026 · checked 2026-09-18 · independently re-checked
16. iron-e1-09 · Observational data · systematic review of postprandial absorption studies
    for example, low-phytate white bread produced a greater 2 h increase in serum iron than high-phytate wholemeal bread (59 vs. 30 μg Fe/100 mL), while exogenous phytase increased iron absorption by 50% for ferrous sulfate and 61% for iron bis-glycine chelate.
    Frontiers in Nutrition, 2026 · checked 2026-09-18 · independently re-checked
17. iron-e1-10 · Observational data · cross-sectional national dietary survey analysis
    Most of the sample population exhibited moderate zinc bioavailability and low iron bioavailability as indicated by the phytate-mineral molar ratios.
    Nutrition Bulletin, 2026 · checked 2026-09-18 · independently re-checked
18. iron-e1-11 · Observational data · cross-sectional national dietary survey analysis
    The median daily dietary phytate intakes were 535.3 mg in 2010 and 658.0 mg in 2017 (p < 0.001).
    Nutrition Bulletin, 2026 · checked 2026-09-18 · independently re-checked
19. iron-07 · Position of an expert body · expert body statement
    The functional deficits that are associated with IDA include gastrointestinal disturbances; weakness; fatigue; difficulty concentrating; and impaired cognitive function, immune function, exercise or work performance, and body temperature regulation.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · extracted
20. iron-08 · Position of an expert body · expert body statement
    IDA in infancy can lead to adverse cognitive and psychological effects, including delayed attention and social withdrawal; some of these effects might be irreversible.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · extracted
21. iron-e1-12 · Position of an expert body · guideline recommendation
    Analysis of the evidence suggested modification of the current haemoglobin cutoffs for defining anaemia for one population group (children 6–23 months of age) and use of the existing cutoff for pregnant women in the second trimester.
    WHO, Guideline on haemoglobin cutoffs to define anaemia in individuals and populations, 2024 · checked 2026-09-18 · independently re-checked
22. iron-e1-13 · Observational data · cross-sectional study
    Applying the new WHO guidelines, anemia prevalence changed from 50% to 42.2% in children aged 6-59 months (62% to 47% in children aged 6-23 months and from 45.9% to 40.6% in children aged 24-59 months).
    PLoS ONE, 2026 · checked 2026-09-18 · independently re-checked
23. iron-e1-14 · Observational data · cross-sectional study
    The proportion of anemia due to ID was 27.5%, due to inflammation was 45.9%, and due to other causes was 26.6%.
    PLoS ONE, 2026 · checked 2026-09-18 · independently re-checked
24. iron-15 · Meta-analysis or systematic review · Cochrane systematic review
    A Cochrane Review showed that daily supplementation with 9 to 90 mg iron reduced the risk of anemia in pregnant women at term by 70% and of iron deficiency at term by 57%.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
25. iron-16 · Meta-analysis or systematic review · Cochrane systematic review
    In the same review, use of daily iron supplements was associated with an 8.4% risk of having a low-birthweight newborn compared to 10.2% with no supplementation.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
26. iron-17 · Meta-analysis or systematic review · systematic review by expert body
    the U.S. Preventive Services Task Force (USPSTF) has concluded that the current evidence is insufficient to assess the balance of benefits and harms of both screening for iron deficiency and IDA in pregnant women and routinely supplementing them with iron
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
27. iron-r3-05 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised trials
    Using a Mantel-Haenszel random-effects model, iron supplementation was associated with reduced self-reported fatigue (standardised mean difference (SMD) -0.38; 95% CI -0.52 to -0.23; I2 0%; 4 trials; 714 participants) but was not associated with differences in objective measures of physical capacity, including maximal oxygen consumption (SMD 0.11; 95% CI -0.15 to 0.37; I2 0%; 9 trials; 235 participants) and timed methods of exercise testing.
    BMJ Open, 2018 · checked 2026-09-17 · independently re-checked
28. iron-r3-06 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised trials
    The pooled analysis found a small, statistically non-significant increase in hemoglobin with daily dosing over alternate-day (MD: 0.28, 95% CI: -0.01 to 0.56, p = 0.06, z = 1.91). Secondary outcomes revealed no significant differences among groups for serum iron, ferritin, transferrin saturation, TIBC, and MCV. Adverse effects were similar between groups (RR: 1.07, 95% CI: 0.86 to 1.34), though metallic taste was more frequent with daily dosing.
    BMC Pharmacology and Toxicology, 2025 · checked 2026-09-17 · independently re-checked
29. iron-p01 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis
    Iron supplementation during pregnancy may reduce maternal anaemia (4.0% versus 7.4%; risk ratio (RR) 0.30, 95% confidence interval (CI) 0.20 to 0.47; 14 trials, 13,543 women; low-certainty evidence)
    Finkelstein et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · independently re-checked
30. iron-p04 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis
    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)
    Finkelstein et al., Cochrane Database of Systematic Reviews, 2024 · checked 2026-09-16 · independently re-checked
31. iron-p07 · Meta-analysis or systematic review · systematic review and meta-analysis
    were at lower risk of anaemia (relative risk = 0.50, 95% CI: 0.34-0.74, P < .001, high certainty, I2 = 42%, number needed to treat (NNT) = 10). There was no difference in birth weight, preterm birth, and rate of caesarean section.
    Ng et al., Family Practice, 2025 · checked 2026-09-16 · independently re-checked
32. iron-p08 · Meta-analysis or systematic review · systematic review and meta-analysis
    Intermittent regimens had lower gastric side effects (relative risk (RR), 0.27; 95%CI, 0.11, 0.69) and better medication adherences (relative risk (RR), 1.6; 95%CI, 1.34, 1.91). There was no clear evidence of a difference in anaemia incidence between the groups (relative risk (RR), 1.09; 95%CI, 0.77, 1.54).
    Tamiru et al., Reproductive Health, 2025 · checked 2026-09-16 · independently re-checked
33. iron-e1-01 · Meta-analysis or systematic review · systematic review of intervention studies
    Statistically significant increases in hemoglobin and/or iron indices (p < 0.05) were observed in 50% (4/8) of studies on pots (relative change/mean difference in Hb: -0.4-1.20 g/dL), and 33.3% (1/3) of studies on ingots (relative change/mean difference in Hb: 0.32-1.18 g/dL).
    Alves et al., PLoS ONE, 2019 · checked 2026-09-18 · independently re-checked
34. iron-e1-02 · Meta-analysis or systematic review · systematic review of intervention studies
    Compliance ranged from 26.7-71.4% daily use of pots to 90-93.9% daily use of ingots.
    Alves et al., PLoS ONE, 2019 · checked 2026-09-18 · independently re-checked
35. iron-e1-03 · Meta-analysis or systematic review · systematic review of intervention studies
    There was marked variation in the effect of iron-containing pots on anemia and iron status. Qualitatively, much of this variation appeared to be explained by differences in the target population studied and intervention compliance.
    Alves et al., PLoS ONE, 2019 · checked 2026-09-18 · independently re-checked
36. iron-e1-04 · Meta-analysis or systematic review · systematic review of intervention studies
    Eight (of eleven) studies did not report on malaria endemicity and nine studies did not report on helminthiasis or schistosomiasis prevalence.
    Alves et al., PLoS ONE, 2019 · checked 2026-09-18 · independently re-checked
37. iron-e1-05 · Randomised controlled trial(s) · randomised controlled trial
    Neither the iron ingot nor iron supplements increased hemoglobin concentrations in this population at 6 or 12 mo.
    Rappaport et al., American Journal of Clinical Nutrition, 2017 · checked 2026-09-18 · independently re-checked
38. iron-e1-06 · Randomised controlled trial(s) · randomised controlled trial
    We do not recommend the use of the fish-shaped iron ingot in Cambodia or in countries where the prevalence of iron deficiency is low and genetic hemoglobin disorders are high.
    Rappaport et al., American Journal of Clinical Nutrition, 2017 · checked 2026-09-18 · independently re-checked
39. iron-13 · Position of an expert body · expert body statement
    Accidental overdose of iron-containing products is a leading cause of fatal poisoning in children under 6.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
40. iron-14 · Position of an expert body · expert body statement
    Acute intakes of more than 20 mg/kg iron (about 1,365 mg iron for a person weighing 150 pounds [lb]) from supplements or medicines can lead to corrosive necrosis of the intestine, which might lead to fluid and blood loss, shock, tissue damage, and organ failure, especially if food is not taken at the same time as the iron.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · independently re-checked
41. iron-10 · Position of an expert body · expert body statement
    High-dose iron supplements can also cause gastrointestinal effects, including gastric upset, constipation, nausea, abdominal pain, vomiting, and diarrhea.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · extracted
42. iron-11 · Position of an expert body · expert body statement
    Without treatment by periodic chelation or phlebotomy, people with hereditary hemochromatosis typically develop signs of iron toxicity by their 30s. These effects can include liver cirrhosis, hepatocellular carcinoma, heart disease, and impaired pancreatic function.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · extracted
43. iron-r2-6 · Meta-analysis or systematic review · systematic review and meta-analysis of randomised trials
    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%].
    Tolkien et al., PLoS One, 2015 · checked 2026-09-17 · independently re-checked
44. iron-r2-8 · Meta-analysis or systematic review · Cochrane systematic review and meta-analysis
    In areas with services, iron (with or without folic acid) may reduce clinical malaria slightly (RR 0.91, 95% CI 0.84 to 0.97; 12 trials, 5777 children; low-certainty evidence). In areas without services, iron (with or without folic acid) may increase clinical malaria slightly (RR 1.15, 95% CI 1.02 to 1.30; 7 trials, 19,754 children; low-certainty evidence).
    Itzkovich et al., Cochrane Database of Systematic Reviews, 2026 · checked 2026-09-17 · independently re-checked
45. iron-12 · Position of an expert body · expert body statement
    The labels for some of these products warn that iron supplements can reduce the absorption of levothyroxine tablets and advise against administering levothyroxine within 4 hours of iron supplements.
    NIH Office of Dietary Supplements, Health Professional Fact Sheet: Iron · checked 2026-09-15 · extracted