Iron supplementation for optimal haemoglobin mass gains at altitude in endurance athletes

Rebecca Hall

doi:10.25907/00686

Dietary iron is crucial for optimising haematological and physiological adaptions to altitude such as increases in haemoglobin mass (Hbmass). At sea-level, some athletes have difficulty maintaining sufficient circulating iron levels due to increased losses and an exercise-induced reduction in uptake from the gastrointestinal (GI) tract. Oral iron supplementation (OIS) therefore provides an important means by which to normalise iron status in athletes with iron deficiency and the more severe, iron deficiency anaemia. OIS also plays a role in maximizing iron availability at times of conditionally increased iron demand such as when athletes are training at elevated altitude. Research has emerged from studies conducted at sea-level that highlight the important impact that timing and dose of OIS have on the amount of iron absorbed from supplementation. This research has mostly been conducted in iron deficient females and its application in the prescription of OIS at altitude in iron replete athletes remains to be investigated. Moreover, the optimisation of iron prescription is especially relevant for athletes training at altitude as very large OIS doses are recommended to meet increased iron demand in response to accelerated erythropoiesis. In practical terms, these large daily doses equate to multiple tablets per day. Research at sea-level would suggest that multiple large doses across a day reduces fractional absorption whilst also being associated with increased GI symptoms, which may discourage supplement adherence and reduce absolute intake. It is apparent that further exploration of OIS prescription is required to understand how to best enhance iron stores in a way that encourages adherence. Thus, the goals of this Master degree were to 1) Compare a SPLIT (2 x 100 mg/AM & PM) versus a SINGLE (1 x 200 mg/PM) dose of iron in terms of Hbmass outcomes after ~3 weeks training at altitude (2,106 m) in elite (male and female) middle-distance runners, and 2) Identify the iron supplementation protocol with the least associated GI symptoms. After providing written consent to participate, athletes were randomly allocated to either the SPLIT or the SINGLE group. Prior to commencing any supplementation and within 24 hours of arrival to altitude, a blood sample was collected for assessment of markers of iron status and related variables: ferritin, total iron, iron saturation, transferrin, total iron binding capacity, unsaturated iron binding capacity, red blood cell count, mean corpuscular volume, mean corpuscular haemoglobin, mean cell Hb concentration, Hb, haematocrit, hepcidin, erythroferrone and C-reactive protein. Hbmass measures were obtained via the CO rebreathing technique within the first 24 hours of athlete’s arrival at altitude. Supplement compliance was confirmed via daily electronic messaging. Blood samples were also collected prior to departure from altitude. The same Hbmass and biochemical measures were repeated prior to departing from the camp. A validated food frequency questionnaire was administered at the start of the altitude camp, while a GI tolerance questionnaire was administered upon arrival, then repeated at the end of weeks 1, 2 & 3 of the camp. A menstrual blood loss questionnaire was completed by each female over the camp for all days where menstrual bleeding occurred. If no menstruation occurred during the camp this was also recorded. Results indicated that both groups increased Hbmass from baseline to POST-camp measures. However, the SINGLE nightly dose group had significantly greater gains (p=0.048, MD 38.39 g, 95% CI [0.386-76.393]) when compared to the SPLIT group despite equivalent iron dose amount for the duration of the camp. GI symptom scores were higher in SINGLE upon completion of weeks 1 and 2 combined when compared to SPLIT, although this equated to only a minor worsening in GI symptoms. Furthermore, differences in GI symptoms between groups were no longer significant upon completion of the camp. Thus, a single 200 mg daily dose of oral iron taken in the evening resulted in superior Hbmass gains during an ~3 week altitude training camp, however this was associated with greater GI symptoms, at least during the initial period of supplementation.

Iron supplementation for optimal haemoglobin mass gains at altitude in endurance athletes

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