Best iron supplement UK (UK 2026)

Iron deficiency is significantly more common in women than men due to menstrual blood loss. Studies show that 27% of UK women aged 19-64 have depleted iron stores (ferritin below 15 micrograms/L), and 5-10% have iron-deficiency anemia. In contrast, iron deficiency in men is usually secondary to disease (GI bleeding, chronic kidney disease) rather than dietary insufficiency. For women, menstrual losses of 30-40 mg iron monthly are typical—heavy periods (menorrhagia) can exceed 100 mg monthly, rapidly depleting stores.

Vegetarians and vegans have elevated deficiency risk because plant-based iron (non-heme iron) is absorbed at 2-20% compared to 15-35% for animal-derived (heme) iron. This is why vegetarian women, in particular, have high deficiency prevalence (up to 40% in some studies). Older adults, particularly women over 70 (when absorption declines), and people with GI disorders (coeliac, Crohn's, post-gastric bypass) are at heightened risk.

The most important point: do not supplement iron without confirmation of deficiency. Iron overload (from excessive supplementation) causes oxidative damage and increases cardiovascular disease and cancer risk. A simple blood test (CBC with differential, ferritin level, possibly serum iron and TIBC) identifies deficiency. If ferritin is above 30 micrograms/L and hemoglobin is normal, iron supplementation provides no benefit.

Ferrous sulfate is the standard, most effective, and cheapest iron supplement. It delivers 65 mg elemental iron per tablet, is well-absorbed (20-30%), and has the most clinical evidence. However, it frequently causes constipation, nausea, and dark/tarry stools (harmless but unpleasant). This form causes more side effects than any other, which is why patient adherence is poor.

Iron bisglycinate (iron bound to the amino acid glycine) is gentler on the GI system—it is absorbed via amino acid transporters, not the standard iron uptake mechanism. Bioavailability is slightly lower than ferrous sulfate (15-20%), but GI tolerance is dramatically better. Most users can take bisglycinate without constipation or nausea. The tradeoff: bisglycinate typically contains 25 mg elemental iron (vs 65 mg for ferrous sulfate) and costs 2-3x more. For people who cannot tolerate ferrous salts, bisglycinate is worth the premium.

Active Iron (a newer technology) uses a special protein-bound form to enhance absorption and reduce GI side effects. Bioavailability is comparable to ferrous sulfate, but user tolerance is better. Active Iron products typically contain 25-30 mg elemental iron and cost moderately more than ferrous sulfate. Real-world evidence suggests Active Iron is well-tolerated by most people.

Iron absorption is enhanced dramatically by vitamin C (ascorbic acid). Taking iron with a source of vitamin C (orange juice, kiwi, citrus fruit, or a 100-200 mg vitamin C tablet) increases absorption by 3-4 fold. This is one of the most important practical adjustments for iron supplementation. If you are taking ferrous sulfate and experiencing slow iron recovery on blood tests, ensure you are always taking it with vitamin C source.

Iron absorption is strongly inhibited by several food components and medications. Tea and coffee contain tannins that bind iron and prevent absorption—consume these at least 1-2 hours away from iron supplementation. Calcium supplements, dairy products, and calcium-fortified foods also inhibit absorption. PPIs (proton pump inhibitors) and H2 blockers reduce stomach acid, essential for iron solubilization. If you take these medications, discuss iron timing with your doctor—you may need to take iron tablets on a different schedule.

Practical timing strategy: take iron supplement on an empty stomach (ideally with vitamin C and water) for best absorption. If GI upset is severe, you can take it with food (reduces absorption but improves tolerance). Never take iron with tea, coffee, dairy, or calcium supplements—wait 2 hours between iron and these substances. Evening dosing often works better than morning because evening GI symptoms are often less noticeable.

Iron supplementation works slowly. Ferritin (iron stores) begins rising within 1-2 weeks of consistent supplementation, but hemoglobin (circulating iron) takes 6-8 weeks to normalize. Most clinical guidelines recommend treating iron deficiency for 8-12 weeks, then retesting to confirm normalization before stopping. Many people stop supplementation too early (after 4-6 weeks) when they feel better but iron stores are not yet repleted—this increases relapse risk.

Expect gradual symptom improvement: fatigue and breathlessness improve within 2-4 weeks as hemoglobin rises. Concentration, mood, and exercise capacity improve by week 4-8. You won't feel dramatically 'better'—the improvement is often subtle (less winded on stairs, clearer thinking). Ironically, this is why many people assume supplementation isn't working and quit early.

For menstruating women with iron deficiency, supplementation alone is often insufficient if menstrual losses are very heavy. Discuss menstrual management with your doctor—hormonal contraception (oral pills, IUS) can reduce losses dramatically. If you supplement iron for 8-12 weeks, retest, and iron deficiency recurs quickly, investigate underlying causes (heavy periods, GI bleeding) rather than just repeating supplementation.