Pre-Altitude Serum Ferritin Levels and Daily Oral Iron Supplement Dose Mediate Iron Parameter and Hemoglobin Mass Responses to Altitude Exposure

PURPOSE: To investigate the influence of daily oral iron supplementation on changes in hemoglobin mass (Hb(mass)) and iron parameters after 2–4 weeks of moderate altitude exposure. METHODS: Hematological data collected from 178 athletes (98 males, 80 females) exposed to moderate altitude (1,350–3,000 m) were analysed using linear regression to determine how altitude exposure combined with oral iron supplementation influenced Hb(mass), total iron incorporation (TII) and blood iron parameters [ferritin and transferrin saturation (TSAT)]. RESULTS: Altitude exposure (mean ± s: 21 ± 3 days) increased Hb(mass) by 1.1% [-0.4, 2.6], 3.3% [1.7, 4.8], and 4.0% [2.0, 6.1] from pre-altitude levels in athletes who ingested nil, 105 mg and 210 mg respectively, of oral iron supplement daily. Serum ferritin levels decreased by -33.2% [-46.9, -15.9] and 13.8% [-32.2, 9.7] from pre-altitude levels in athletes who supplemented with nil and 105 mg of oral iron supplement daily, but increased by 36.8% [1.3, 84.8] in athletes supplemented with 210 mg of oral iron daily. Finally, athletes who ingested either 105 mg or 210 mg of oral iron supplement daily had a greater TII compared with non-supplemented athletes (0 versus 105 mg: effect size (d) = -1.88 [-2.56, -1.17]; 0 versus 210 mg: effect size (d) = -2.87 [-3.88, -1.66]). CONCLUSION: Oral iron supplementation during 2–4 weeks of moderate altitude exposure may enhance Hb(mass) production and assist the maintenance of iron balance in some athletes with low pre-altitude iron stores.