Daily iron supplementation for improving anaemia, iron status and health in menstruating women.

Systematic review and meta-analysis of controlled trials in menstruating women of reproductive age who were not pregnant or lactating. Some included participants were iron deficient or anaemic at baseline, and the review drew on active iron arms from a large number of randomized studies conducted in varied community, student, athletic, donor, and occupational populations.

Daily oral iron supplementation was evaluated across trials, using a wide range of formulations and elemental iron doses, from low-dose regimens such as 5 to 30 mg/day up to higher-dose schedules around 60 to 120 mg/day or more. Most interventions were given for 1 to 3 months; some comparisons also included coadministration with vitamin C or folic acid, but iron was the primary active supplement.

Daily iron supplementation lowered anaemia and iron deficiency and increased haemoglobin and iron stores. Pooled effects were favorable for anaemia prevalence (RR 0.39), haemoglobin (MD 5.30), ferritin (MD 10.27), and transferrin saturation (MD 5.98), and some trials also showed improved maximal exercise performance, selected submaximal performance measures, and reduced fatigue. Gastrointestinal side effects increased, with higher elemental iron doses causing more adverse effects. Vitamin C coadministration may improve anaemia reduction in some comparisons, but cognitive and broader psychological benefits were limited and inconsistent.

The evidence base was heterogeneous, with substantial variation in dose, formulation, duration, and participant baseline iron status. Many trials had risk-of-bias concerns, and reporting of non-haematologic outcomes such as cognition and psychological health was limited. Mortality was not reported, so benefits and harms are best interpreted for haematologic and selected functional outcomes only.