Iron supplementation benefits physical performance in women of reproductive age: a systematic review and meta-analysis.

Systematic review and meta-analysis of controlled trials in women of reproductive age who were not pregnant or lactating. Included participants varied in iron status, ranging from iron-deficient or anemic to non-anemic or mixed, and in training status, from trained athletes to non-trained women; some studies included adolescents.

Daily oral iron supplementation was evaluated across trials, most commonly as elemental iron given as ferrous sulfate, with doses ranging from 1 mg/day to 150 mg/day and one regimen using 100 mg elemental iron twice per day. Some studies also paired iron with specific diet or exercise conditions, such as a low-iron diet or an exercise regimen, but the primary intervention was oral iron supplementation.

Daily oral iron supplementation improved maximal and submaximal exercise performance in women of reproductive age. The clearest benefits were seen in iron-deficient and trained women, with improved maximal aerobic capacity and better efficiency during submaximal exercise; some evidence also suggested benefit when baseline iron status was not established. Across the review, maximal VO2 max and other maximal outcomes generally favored iron in several subgroups, and submaximal measures such as heart rate and percentage of VO2max required also improved. Adverse gastrointestinal events were reported in at least one trial.

The evidence base was heterogeneous, with variation in iron status, training status, doses, and co-interventions across trials. Only a small number of high-quality studies were available, and per-arm baseline and post-intervention outcome data were not consistently reported in the extracted source. Adverse gastrointestinal effects were noted in at least one trial, and generalizability beyond women of reproductive age is limited.