PURPOSE: To determine if a split daily 200mg elemental iron dose (2x100mg) is superior to a single daily iron dose (1x200mg) for optimal haemoglobin mass (Hbmass) gains at altitude, while minimizing gastro-intestinal (GI) discomfort.
METHODS: Twenty-six elite male and female runners attended a 3.1±0.3week training camp at 2,106m altitude in Flagstaff, AZ. A two-group design, randomized and stratified to baseline Hbmass, sex and ferritin, was implemented as: 1) split dose of 2 x 100mg daily (AM & PM; SPLIT) vs; 2) single dosing of 1 x 200mg daily (PM only, SINGLE) elemental iron (ferrous fumarate). Two participants were excluded (baseline ferritins <30μ/mL; n=24 for final analysis). Hbmass measures (via the carbon monoxide rebreathing technique) and venepuncture draws were completed upon immediate (±2 days) arrival and departure of the camp for ferritin, hepcidin and erythroferrone (ERFE) analysis. Validated food frequency (FFQ), GI, menstrual blood loss (MBL) and training questionnaires were implemented throughout the camp. Univariate analysis was used to compare Hbmass outcomes; accounting for the covariates of dietary iron intake, menstrual blood losses and training volume. The alpha-level was set at p<0.05. Data are reported as means ± standard deviation.
RESULTS: Both groups significantly increased Hbmass post-camp, but SINGLE was significantly higher than SPLIT (SINGLE: 867.3±47.9g, SPLIT: 828.9±48.9g, p=0.048). GI scores were worse (greater) in SINGLE for weeks 1 & 2 combined (SINGLE: 18.0±6.7 points, SPLIT: 11.3±6.9 points, p=0.025), however, GI tolerance improved in SINGLE, and the between group difference was no longer apparent by week 3 (p=0.335). ERFE significantly decreased in both groups (~28.5%), however, no between group differences existed (p>0.05). Hepcidin showed a tendency to decline (~33.5%), with no difference between groups (p>0.05). There were no between group differences in FFQ, MBL or average daily training outcomes (p>0.05).
CONCLUSION: A single nightly 200mg dose of elemental iron (ferrous fumarate) was superior to a split dose for optimizing changes in Hbmass at 2,106m altitude in elite runners over a 3.1±0.3week training camp. Observed differences may be due to a greater acute hepcidin response in the SPLIT group, however, more research is required to explore the mechanism.