Optimal timing and frequency of iron supplementation for athletes
By: Rebecca Hall, Advanced Accredited Sports Dietitian & Dr Trent Stellingwerff, PhD, Director of Performance Solutions, Canadian Sports Institute Pacific, Victoria, BC, Canada
Maintaining sufficient iron stores is paramount for athletes, given iron is a vital constituent of oxidative metabolism and oxygen transport via haemoglobin and myoglobin, as well as essential enzymes for energy production pathways (1). Many endurance athletes struggle to maintain iron stores due to exacerbated iron losses and reduced iron availability in the post training period (2). Consequently many athletes commence iron supplementation, ideally recommended by a sports medicine physician, during a period of demonstrated deficiency or increased need, such as training at elevated altitude (3). Nevertheless, timing and frequency of iron supplementation for optimal absorption and minimal gastrointestinal (GI) distress has only more recently been explored.
Although the clinical definition of iron deficiency includes varying cut offs for serum ferritin (SF <12 µg/L to <20 µg/L), the incidence of iron deficiency (ID) without anaemia is thought to be as high as 17% in male and 50% in female endurance athletes, with higher rates in runners and triathletes (1, 4). Furthermore, studies have shown that ID without anaemia can decrease adaptations to training and potentially performance (5). Furthermore, endurance athletes face increased iron losses through sweat, urine, the GI tract, haemolysis (foot strike and muscle contraction) and blood loss associated with injury (6-9). This is exacerbated in female athletes due to menstrual losses equating to ~1 mg/day of menses (10, 11). Furthermore, restrictive eating behaviours and/or diets (e.g. vegetarianism) potentially result in suboptimal dietary iron intake (10, 12, 13). Finally, uptake from the gut, availability in circulation and iron recycling is impaired following high intensity and longer duration exercise due to the exercise-induced increase of the iron regulatory peptide hormone hepcidin (2, 14-17). Taken together, these mechanisms can result in a “perfect storm” of increased risk for iron depletion for many athletes.
