Effect of iron supplementation on exercise performance of women with non-anemic iron deficiency or iron deficiency anemia - a systematic review and meta-analysis

Female athletes have been considered a risk group for non-anemic iron deficiency (NAID) and iron deficiency anemia (IDA) given iron loss situations (i.e., excessive blood lost during a menstrual cycle, eccentric muscle contraction, and sweating). Iron supplementation should be a strategy to increase both iron levels and physical exercise performance. To verify the effect of iron supplementation on the exercise performance of women with NAID or IDA, a systematic review and meta-analysis was conducted (CRD42021245452). Inclusion criteria comprised randomized or non-randomized clinical trials with a control group that determined the effect of iron supplementation associated with endurance exercise on women’s exercise performance. A search of the MEDLINE/PubMed, LILACS, SciELO, and Scopus databases was performed in February 2025 including all articles. A total of 2122 studies were initially identified. Following exclusions, 15 studies with a total of 380 participants were included. Iron supplementation did not improve exercise performance assessed during time-to-exhaustion (TTE; MD: 0.76 min; 95% CI: -0.13; 1.65; p=0.067) or time trial (TT; MD: -1.78 min; 95% CI: -3.88; 0.333 min; p=0.059) protocols. Still, by combining TTE and TT studies in the same analysis, we observed a non-significant effect on exercise performance (SMD: 0.97; 95% CI: -0.49 to 2.44; p=0.139). Moreover, although iron supplementation led to consistent improvements in hemoglobin and serum ferritin levels, its effects on cardiorespiratory fitness and exercise performance were mixed. We observed a moderate and statistically significant improvement in V̇O₂max/V̇O₂peak (SMD: 0.70; 95% CI: 0.08 to 1.31; p = 0.030). However, this effect was no longer statistically significant when studies involving women with anemia were excluded (SMD: 0.61; 95% CI: -0.05 to 1.27; p = 0.068), suggesting that the observed improvement in cardiorespiratory fitness may be primarily driven by this subgroup. In contrast, no significant effects were found on exercise performance outcomes such as TTE or TT performance. Although iron supplementation led to improvements in hemoglobin and serum ferritin levels, its effects on exercise performance and cardiorespiratory fitness were limited.