Iron
Essential for haemoglobin and energy production
What is Iron?
Iron is an essential mineral and central component of haemoglobin — the protein in red blood cells that carries oxygen from lungs to tissues. It's also a component of myoglobin (muscle oxygen storage), cytochromes (mitochondrial energy production), and numerous enzymes. Iron deficiency is the most common nutritional deficiency worldwide and the most common cause of anaemia. In the UK, iron deficiency affects approximately 25% of menstruating women and is common in pregnant women, athletes, and vegetarians.
How it works
Haemoglobin contains four haem groups, each with a central iron atom that binds oxygen. Without adequate iron, haemoglobin production is impaired, red blood cells become small and pale (microcytic, hypochromic), and oxygen delivery to tissues falls. This manifests as fatigue, breathlessness, poor concentration, and reduced exercise capacity. Iron also plays roles in the electron transport chain (mitochondrial energy production) and dopamine/noradrenaline synthesis — explaining the cognitive and mood effects of deficiency.
What the evidence shows
Iron deficiency and iron-deficiency anaemia are extensively documented medical conditions with well-established supplementation protocols. Multiple RCTs confirm: supplementation restores haemoglobin, improves fatigue, improves cognitive function in deficient individuals, and improves exercise capacity. A 2012 Cochrane review confirmed iron supplementation significantly improves Hb, ferritin, and cognitive development. The evidence is particularly strong in women of reproductive age.
When to expect results
Iron stores beginning to replenish. No perceptible improvement yet — it takes time to build haemoglobin.
Haemoglobin levels starting to rise. Some improvement in energy and breathlessness in those most deficient.
Significant improvement in fatigue, exercise tolerance, and cognitive function. Haemoglobin approaching normal.
Ferritin (iron stores) fully restored. Sustained energy, mood, and immune function. Symptoms should be fully resolved.
Dosing
For treatment of confirmed deficiency: 100–200mg elemental iron daily (prescribed, or under GP guidance with ferritin monitoring). For prevention/maintenance in at-risk groups: 14–18mg elemental iron daily. The UK RNI is 8.7mg for men and postmenopausal women, 14.8mg for menstruating women. Note: 'ferrous sulphate 200mg' contains ~65mg elemental iron — read labels for elemental iron content.
Forms to choose
Ferrous (2+) forms are better absorbed than ferric (3+) forms. Ferrous sulphate: most studied, most affordable, but GI side effects common. Ferrous bisglycinate (iron glycinate): significantly better tolerated, similar or better bioavailability — the premium choice. Ferrous gluconate and ferrous fumarate: intermediate options. Take on empty stomach for best absorption, but with food if GI upset occurs. Avoid with calcium, coffee/tea (tannins), or high-fibre meals — they all impair absorption.
Who benefits most
Menstruating women (especially heavy periods), pregnant women, vegans and vegetarians (non-haem iron from plants is less bioavailable), endurance athletes (foot-strike haemolysis, GI blood loss, high iron demand), people with IBD (malabsorption and blood loss), anyone with symptoms of deficiency (fatigue, breathlessness, poor concentration, pale skin, brittle nails).
Who should avoid / caution
Men and postmenopausal women should NOT routinely supplement iron without confirmed deficiency — iron overload is harmful. People with haemochromatosis must avoid iron supplements entirely. Always test before supplementing.
Interactions & stacking
Vitamin C (ascorbic acid) converts ferric iron to the more absorbable ferrous form and chelates iron to enhance absorption. Always take iron with vitamin C or a vitamin C-rich food.
Calcium directly competes with iron for absorption. Separate iron supplementation from dairy and calcium supplements by at least 2 hours.
Tannins in tea and coffee bind iron and reduce absorption by up to 60%. Do not drink tea or coffee within 1 hour of taking iron.
Very high iron can compete with zinc absorption at the intestinal level. Avoid megadosing both simultaneously.
Safety & side effects
Constipation, dark stools, nausea, and stomach cramps are common with ferrous sulphate at standard doses. Ferrous bisglycinate has significantly fewer GI side effects. Dark stools are normal and harmless. Iron overload (haemochromatosis) is a risk if supplementing without confirmed deficiency — always test serum ferritin before supplementing iron. Excess iron is pro-oxidant.
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This information is for educational purposes only and does not constitute medical advice. Always consult your GP or a qualified healthcare professional before starting any new supplement, particularly if you are pregnant, breastfeeding, have a medical condition, or are taking prescription medication.