Strong evidenceGeneral health

Iron

Iron is one of the few supplements with unambiguous, large benefits — but only if you are actually deficient. Taking it without a confirmed low ferritin is at best pointless and at worst dangerous, and how you dose it matters more than most people realise.

What the science says

Prevents anaemia and iron deficiency in pregnancy Strong evidence
A Cochrane review of 61 trials (over 43,000 women) found daily oral iron reduced maternal anaemia at term by 70% (RR 0.30, 95% CI 0.19-0.46) and iron deficiency at term by 57% (RR 0.43, 95% CI 0.27-0.66), with fewer low-birthweight babies (8.4% versus 10.3%, RR 0.84). This is the strongest evidence base for any iron indication.
Reduces fatigue in non-anaemic women with low ferritin Moderate evidence
A randomised trial in 198 menstruating women with unexplained fatigue and ferritin below 50 mcg/L found 80 mg/day ferrous sulfate for 12 weeks reduced fatigue by 47.7% versus 28.8% on placebo (difference -18.9%, 95% CI -34.5 to -3.2, P=0.02). There was no effect on quality of life, depression or anxiety, and the result applies only to women with genuinely low ferritin — not to tired people in general.
Alternate-day single doses absorb better than daily split doses Moderate evidence
A dose of iron raises hepcidin for 24 hours or more, blunting absorption of the next dose. In two randomised absorption studies in iron-depleted women, alternate-day dosing gave higher fractional absorption (21.8% versus 16.3%) and more total absorbed iron (175.3 mg versus 131.0 mg, P=0.0010) than consecutive-day dosing at the same total intake, and twice-daily splitting was worse still. Alternate-day dosing also halves the GI side-effect exposure.

Dosage & safety

Studied doseFor documented deficiency: 60-120 mg elemental iron, given as a single morning dose on alternate days rather than split through the day. Ferrous sulfate 325 mg provides 65 mg elemental; ferrous gluconate 325 mg provides 38 mg; ferrous bisglycinate is gentler on the gut at comparable absorption. Vitamin C modestly aids uptake; coffee, tea, calcium, dairy and phytate inhibit it. Recheck ferritin at 3 months — refilling stores typically takes 3-6 months beyond haemoglobin normalisation.

SafetyConstipation, black stools, nausea and abdominal pain are common and dose-related, and are the main reason people abandon treatment. Acute overdose is a leading cause of fatal poisoning in young children — keep it locked away. Do not supplement without a documented low ferritin: people with hereditary haemochromatosis, thalassaemia or other iron-loading disorders can be seriously harmed, and excess iron may feed gut pathogens. Iron reduces absorption of levothyroxine, tetracyclines, quinolones, levodopa and bisphosphonates — separate by 2-4 hours. Proton pump inhibitors reduce iron absorption. In malaria-endemic regions, routine iron supplementation of children should be paired with malaria surveillance and treatment.

Scientific references

Daily oral iron supplementation during pregnancy
Peña-Rosas JP, De-Regil LM, Garcia-Casal MN, Dowswell T — Cochrane Database of Systematic Reviews, 2015
Effect of iron supplementation on fatigue in nonanemic menstruating women with low ferritin: a randomized controlled trial
Vaucher P, Druais PL, Waldvogel S, Favrat B — CMAJ, 2012
Iron absorption from oral iron supplements given on consecutive versus alternate days and as single morning doses versus twice-daily split dosing in iron-depleted women: two open-label, randomised controlled trials
Stoffel NU, Cercamondi CI, Brittenham G, et al. — The Lancet Haematology, 2017

Where to buy

California Gold Nutrition, Iron, as Ferrous Bisglycinate Chelate and Yellow Dock Root, 4 fl oz (118 ml)

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