Energy deficit increases hepcidin and exacerbates declines in dietary iron absorption following strenuous physical activity: a randomized-controlled cross-over trial

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Strenuous physical activity promotes inflammation and depletes muscle glycogen, which may increase the iron regulatory hormone hepcidin. Hepcidin reduces dietary iron absorption and may contribute to declines in iron status frequently observed following strenuous physical activity. To determine the effects of strenuous physical activity on hepcidin and dietary iron absorption and whether energy deficit compared with energy balance modifies those effects. This was a randomized, cross-over, controlled-feeding trial in healthy male subjects (n=10, mean±SD age: 22.4±5.4 y, weight: 87.3±10.9 kg) with sufficient iron status (serum ferritin 77.0±36.7 ng/mL). Rest measurements were collected before participants began a 72-h simulated sustained military operation (SUSOPS), designed to elicit high energy expenditure, glycogen depletion, and inflammation, followed by a 7-d recovery period. Two 72-h SUSOPS trials were performed where participants were randomly assigned to consume either energy matched (±10%) to their individual estimated total daily energy expenditure (BAL) or energy at 45% of total daily energy expenditure to induce energy deficit (DEF). On the rest day and at the completion of BAL and DEF, participants consumed a beverage containing 3.8 mg of a stable iron isotope, and plasma isotope appearance was measured over 6 h. Muscle glycogen declined during DEF and was preserved during BAL (-188±179 mmol/kg, P-adjusted<0.01). Despite similar increases in interleukin-6, plasma hepcidin increased during DEF but not BAL, such that hepcidin was 108% greater during DEF compared with BAL (7.8±12.2 ng/mL, P-adjusted<0.0001). Peak plasma isotope appearance at 120 min was 74% lower with DEF (59±38% change from 0 min) and 49% lower with BAL (117±81%) compared with rest (230±97%, P-adjusted<0.01 for all comparisons). Strenuous physical activity decreases dietary iron absorption compared with rest. Energy deficit exacerbates both the hepcidin response to physical activity and declines in dietary iron absorption compared with energy balance. This trial was registered at clinicaltrials.gov as NCT03524690.