Marginal iron deficiency without anemia impairs aerobic adaptation among previously untrained women.

Previously untrained, marginally iron-depleted, nonanemic premenopausal women aged 18-33 years were studied in a training trial. The active iron arm included 22 participants and was compared with placebo while all participants completed supervised aerobic training.

Oral iron supplementation with ferrous sulfate: 50 mg FeSO4 (8 mg elemental iron) per capsule, taken twice daily for 6 weeks. Capsules were taken with citrus juice to enhance absorption and with meals to reduce side effects; the study compared iron with placebo during concurrent aerobic training.

Oral iron improved iron status and appeared to enhance aerobic adaptation during training in this iron-depleted, nonanemic population. In the iron group, absolute VO2 max increased from 2.11 ± 0.09 to 2.48 ± 0.08 L/min, and relative VO2 max increased from 49.1 ± 2.0 to 57.6 ± 1.8 mL·kg FFM^-1·min^-1; RERmax fell from 1.18 ± 0.02 to 1.06 ± 0.02. Iron markers also improved: transferrin saturation rose from 11.5 ± 5.2% at baseline to 27.1 ± 5.3% after treatment, ferritin increased from 8.0 ± 2.2 to 12.7 ± 2.0, and sTfR decreased from 12.6 ± 3.7 to 7.4 ± 1.9. The report notes significant group-by-time effects for transferrin saturation and group effects for ferritin and transferrin saturation, supporting a beneficial effect of supplementation.

The active intervention arm was small, with only 22 participants, and the intervention period was short at 6 weeks alongside 4 weeks of training. The population was narrowly defined as young, untrained, nonanemic, iron-depleted women from a single academic setting, which limits generalizability. Not all hematologic indices changed consistently, so the physiologic response was strongest for iron-status markers and aerobic performance rather than anemia-related measures.