Iron deficiency, supplementation, and sports performance in female athletes: A systematic review.

Background: Iron facilitates key biological functions underpinning sports performance, and up to 60% of female athletes experience iron deficiency. However, the effects of iron deficiency on sports performance in female athletes is unclear, as are the degree of benefits of iron supplementation (FeSup). This study characterizes the effects of iron deficiency and FeSup on sports performance in high-level female athletes.

Methods: Searches of the electronic databases Medline, SPORTDiscus, Web of Science, Scopus, and CINAHL were performed in July 2023. Studies were included that evaluated the effects of iron deficiency or FeSup on sports performance in high-level (maximal oxygen uptake [VO_2max] > 45 mL/kg/min, or trained > 5 h/week) iron deficient (ID) (serum ferritin [sFer] < 40 µg/L) female athletes. Studies were assessed using a modified Downs and Black Quality Assessment Checklist.

Results: A total of 23 studies comprising 669 athletes (age range: 13-47 years) across 16 sports were included in the review. Iron deficiency negatively affects endurance performance by 3%-4%. However, endurance performance improved by 2%-20% when ID athletes were treated with 100 mg/day of elemental iron for up to 56 days via oral supplementation, or bi-daily via parenteral administration over 8-10 days. ID non-anemic athletes with low sFer stores may be predisposed to reduced maximal aerobic capacity. However, maximal aerobic capacity improved by 6%-15% following 16-100 mg/day of elemental iron for 36-126 days. Isokinetic strength and anaerobic power performance may be impeded (-23% to +4%) among ID athletes, but the effect of FeSup on anaerobic power varied markedly (-5% to +9%) following 100 mg/day of elemental iron over 42-56 days, or 100 mg of elemental iron bi-daily over 8-10 days. The quality of studies was moderate (77%), ranging from low (57%) to high (100%). Moststudies (n = 18) contained group sizes ≤ 20 athletes, thus limiting the likelihood of detecting significant effects (statistical power > 0.80).

Conclusion: High-level ID female athletes experience a negative impact on endurance performance, which can be improved by supplementing with ∼100 mg of elemental iron per day or bi-daily. The decrements in other performance parameters characterizing a range of sports coincide with the severity of iron deficiency.