Iron for Chronic Fatigue

Iron corrects the fatigue it causes. That sounds circular, but it is the whole point: the evidence supports iron for tiredness driven by low iron stores, and it says nothing useful about tiredness in people whose iron is normal. The important nuance is that you do not need to be anaemic. Randomised trials in non-anaemic women with low ferritin show measurable reductions in fatigue, which means haemoglobin alone is the wrong screening test. Ferritin, transferrin saturation and a marker of inflammation such as CRP together give the real picture. Before supplementing, the cause matters more than the dose. Heavy menstrual bleeding, coeliac disease, gastrointestinal blood loss and poor intake all present the same way in a blood test, and only one of them is fixed by tablets.

Expectations should be set by the timeline. Subjective energy often improves within four to six weeks, haemoglobin responds over two to three months, and ferritin stores take three to six months of continued treatment to rebuild. If ferritin is comfortably normal and fatigue persists, iron is the wrong lever. Thyroid function, B12 and folate, sleep-disordered breathing, depression, coeliac disease and medication effects account for far more unexplained fatigue than iron does.

Iron is not just about haemoglobin. It sits at the catalytic centre of the iron-sulphur clusters and haem groups in mitochondrial complexes I, II, III and IV, so oxidative phosphorylation capacity falls before red cell counts do. That is the mechanistic reason non-anaemic iron deficiency produces genuine fatigue and reduced exercise tolerance. Iron is also a cofactor for tyrosine hydroxylase and tryptophan hydroxylase, the rate-limiting enzymes for dopamine and serotonin synthesis, and for myoglobin oxygen storage in muscle. Absorption is tightly controlled by hepcidin, which rises with inflammation and after each iron dose, blocking ferroportin export from enterocytes. That single regulatory loop explains both why inflammation causes functional deficiency and why alternate-day dosing absorbs better than daily dosing.

The modern approach uses less iron, less often. Because each dose raises hepcidin for roughly 24 hours, 60 to 120 mg of elemental iron on alternate days absorbs more total iron than the same amount split daily, with markedly fewer gastrointestinal complaints. Take it on an empty stomach with vitamin C or orange juice, and keep tea, coffee, calcium, dairy and antacids at least two hours away. Recheck ferritin and haemoglobin after eight to twelve weeks, then continue for three months beyond normalisation to refill stores rather than stopping at the first normal result.

A 2012 randomised controlled trial in non-anaemic menstruating women with low ferritin found iron supplementation significantly reduced fatigue scores compared with placebo, and a 2018 systematic review reached the same conclusion for fatigue and physical capacity in non-anaemic iron-deficient women. A 2016 Cochrane meta-analysis of daily iron supplementation confirms improvements in anaemia, iron status and related health outcomes. The caveats are consistent. Trials enrolled iron-deficient participants, so results do not transfer to people with normal ferritin. Fatigue outcomes are subjective and partly susceptible to unblinding through side effects, and effect sizes are moderate rather than transformative. Nothing here supports iron as a general energy supplement.

Gastrointestinal effects dominate: nausea, epigastric pain, constipation, and harmless black stools. Lower doses, alternate-day schedules and ferrous bisglycinate all reduce them, and constipation usually responds to fluid, fibre and, if needed, a stool softener. The serious concerns are iron overload and paediatric poisoning. Never supplement without confirmed deficiency, because unnecessary iron accumulates in liver, heart and pancreas, and people with haemochromatosis genotypes are at particular risk. Iron tablets are a leading cause of fatal poisoning in young children, so keep them in child-resistant containers out of reach.

Iron is a chelation magnet. Most of its interactions are absorption problems in both directions, solved by spacing doses rather than stopping either drug.