Quick answer
- The NHS says 17 mg or less a day of iron from supplements is unlikely to cause harm; treatment doses for anaemia are prescribed by a GP. Daily needs: 8.7 mg for men and women over 50, 14.8 mg for women aged 19 to 49.
- Iron reduces tiredness only if you are deficient. Get a ferritin test first: below 30 µg/l suggests iron deficiency.
- EFSA considers up to 40 mg of iron a day in total safe; Germany's BfR recommends no more than 6 mg per daily dose in over-the-counter supplements.
- Taking iron on alternate days may improve absorption. Avoid coffee, tea and calcium around the dose, and take it with vitamin C.
- Bisglycinate is often better tolerated than ferrous sulphate at a lower dose; liposomal forms have little independent evidence.
Key numbers
- UK daily need (NHS)
- 8.7 mg; 14.8 mg women 19–49
- UK figure for supplements (NHS)
- 17 mg/day or less
- Unlikely to cause harm; follow your GP if prescribed more.
- Reference intake on labels (NRV)
- 14 mg/day
- Safe level of total intake (EFSA, 2024)
- 40 mg/day
- Germany (BfR guidance)
- 6 mg per daily dose
- Higher doses belong in medicines prescribed after a test.
- Ferritin suggesting deficiency
- below 30 µg/l
- Minimum for an authorised claim
- 2.1 mg per daily dose
What these terms mean: NRV upper levels (NHS, EFSA) maximum levels by country daily dose
How to choose
- Test before you buy: ferritin and a blood count. Tiredness has many causes, and iron only helps if you are low.
- If you are deficient, follow your GP's dose: treatment doses are far above what a food supplement should contain.
- For mild needs (heavy periods, vegetarian diet), a low-dose bisglycinate product is usually easiest on the stomach.
- Take it with vitamin C or fruit, away from coffee, tea, dairy and calcium supplements.
- Men and post-menopausal women should not take iron without a test.
Iron forms compared
| Form | What it is | Good to know |
|---|---|---|
| Ferrous sulphate | Classic iron salt, common in medicines | Cheap and effective; more stomach upset and constipation |
| Ferrous fumarate / gluconate | Other iron(II) salts | Similar to sulphate; gluconate gives less iron per mg |
| Iron bisglycinate | Iron bound to the amino acid glycine | Often better tolerated at lower doses |
| Liposomal / “sucrosomial” iron | Iron in a fat or sugar coating | Marketed as gentle; little independent evidence |
| Liquid tonics with plant extracts | Iron gluconate in a fruit and herb base | Low dose; check iron per daily serving |
What the evidence says
Iron deficiency is common in women who menstruate, pregnant women, frequent blood donors and people on plant-based diets. In a Swiss trial of 198 tired women without anaemia but with low ferritin, iron reduced fatigue scores by 48%, against 29% with placebo. Without deficiency, extra iron brings no benefit, and iron that the body cannot get rid of accumulates.
Absorption is better when iron is taken in the morning, every other day, with vitamin C and away from coffee, tea and calcium, according to studies in iron-depleted women. Read iron and tiredness for the ferritin levels and dosing in detail.
What the label may legally claim
Authorised claims (GB and EU registers)
- Contributes to the reduction of tiredness and fatigue
- Contributes to normal formation of red blood cells and haemoglobin, and normal oxygen transport
- Contributes to normal cognitive function and normal function of the immune system (all from 2.1 mg per daily dose)
Not authorised in GB or the EU
- More energy if you are not iron-deficient
- Treating anaemia (that needs a diagnosis and a medicine)
How health claims work (UK & EU): health claims
Products we have checked
Label data checked by NutriMetrics for products sold in Spain and Germany. UK product checks are next. Sorted alphabetically, not ranked.
| Product | Per daily dose | Sold in | Label |
|---|---|---|---|
| Solgar Gentle Iron 25 mg1 capsule a day | 25 mg · bisglycinate (Ferrochel) | Spain (not yet confirmed) · Germany (not yet confirmed) | Source |
Who should be careful
- Children: keep iron supplements out of reach; accidental overdose is dangerous for young children.
- Haemochromatosis or other iron-overload conditions: do not take iron.
- Medicines: iron reduces the absorption of levothyroxine and some antibiotics; take them hours apart. Constipation and dark stools are common.
FAQ
Should I take iron if I'm tired?
Only if a blood test shows low iron. In a trial of tired women without anaemia but with low ferritin, iron reduced fatigue more than placebo. Without deficiency, there is no benefit and some risk.
Which iron supplement is best tolerated?
Iron bisglycinate at a modest dose is often easier on the stomach than ferrous sulphate. Taking it every other day may also reduce side effects and improve absorption.
How much iron is too much?
The NHS says 17 mg or less a day from supplements is unlikely to cause harm; higher doses should be prescribed by your GP. EFSA set a safe level of 40 mg a day for total intake in 2024, and Germany's BfR advises no more than 6 mg per daily dose in a supplement.
Sources
- NHS — Iron
- DHSC — Great Britain nutrition and health claims (NHC) register
- NIH Office of Dietary Supplements — Iron fact sheet for health professionals
- EFSA (2024) — Scientific opinion on the tolerable upper intake level for iron (safe level 40 mg/day)
- Verbraucherzentrale — Iron, quality not quantity (BfR 6 mg recommendation; German)
- Vaucher P et al. Iron supplementation and fatigue in non-anaemic menstruating women with low ferritin. CMAJ, 2012
- Stoffel NU et al. Iron absorption on consecutive versus alternate days. Lancet Haematol, 2017
- European Commission — EU Register of nutrition and health claims
Information only, not medical advice. No product on this page is a paid placement.