Factors Influencing Iron Metabolism in Female and Male Athletes

Abstract

“Athletes are at risk for iron deficiency” has long been the dominant narrative in sport science when bringing iron and athletic performance together. This perspective is not unsupported, prevalence data speak for themselves, but it seems to shrink a highly complex physiology into a single outcome. Iron metabolism represents a tightly regulated network that underlies complex regulatory mechanisms. Its involvement spreads across multiple physiological systems, including the hematological and immune system, energy metabolism and oxygen transport. This large involvement creates a platform that increases its susceptibility to influencing factors. Athletes with their extraordinary lifestyle place unique stress on iron homeostasis, often have elevated iron requirements and may therefore be particularly susceptible to iron deficiency. High training loads, exposure to hypoxia, altered energy availability, and sex-specific factors are only a few factors placing substantial influence on iron balance. Therefore, this dissertation project set out to investigate these interacting dynamics, rather than treating iron deficiency as an isolated endpoint. The aim was to advance the mechanistic understanding of iron regulation, and to inform evidence-based practical guidelines. To address this aim, the dissertation integrates evidence from a narrative review and multiple original empirical studies conducted in athletic populations. The project opened with a narrative review synthesizing current knowledge iron-related challenges and practical prevention methods for iron deficiency in athletes. This background guided three original studies on distinct but interrelated stressors of iron homeostasis. Under controlled normobaric hypoxia, athletes demonstrated increased erythropoietic iron demand alongside alterations in immune-related markers, highlighting competition for iron between physiological systems. Menstrual blood loss appeared as a recurrent iron stressor in female athletes, showing that despite chronically lower ferritin concentrations, hematological function and oxygen transport capacity were maintained, indicative of adaptive iron redistribution. Finally relative energy availability was identified as a key determinant of systemic iron status in elite athletes, linking metabolic strain to reduced iron stores independent of dietary iron intake. Taken together, this cumulative work places iron within the framework of network physiology. Iron emerges not as an isolated hematological variable, but as a dynamic mediator within an interconnected system of adaptations, in which influencing factors force a regulated symmetry under sustained demand. This perspective provides a conceptual basis for a broader yet more specific monitoring and management strategies that account systemic interactions.