Red-s in endurance athletes — skeletal consequences of chronic low energy availability

Background. Relative Energy Deficiency in Sport (RED-S) is an increasingly recognized health problem among endurance athletes. The main mechanism leading to the development of RED-S is low energy availability (LEA), resulting from insufficient energy intake in relation to exercise energy expenditure. Chronic energy deficiency may lead to hormonal, metabolic and regenerative disturbances, as well as impaired bone health and an increased risk of stress fractures. Aim. The aim of this review was to summarize current knowledge regarding RED-S in endurance athletes, with particular emphasis on the impact of low energy availability on bone health and the risk of stress fractures. Material and methods. This review was based on an analysis of scientific literature available in PubMed and Google Scholar databases. Publications concerning RED-S, low energy availability, bone health, hormonal mechanisms, and stress fractures in endurance athletes were included. The analysis included review articles, observational studies, cross-sectional studies, and expert consensus statements published mainly between 2014 and 2026. Results. The analyzed studies indicate that chronic LEA contributes to disturbances in the hypothalamic–pituitary–gonadal axis, reduced sex hormone concentrations, increased cortisol levels, and decreased IGF-1 concentrations. These hormonal alterations negatively affect bone remodeling processes, leading to decreased bone mineral density and increased susceptibility to bone stress injuries and stress fractures. Female athletes with menstrual disturbances and adolescent athletes during the period of peak bone mass acquisition appear to be particularly vulnerable. RED-S affects both elite and recreational athletes. Conclusions. RED-S constitutes a significant health concern in endurance sports. Early identification of LEA symptoms, appropriate nutritional support, and proper training load management are essential for preventing long-term bone complications. Multidisciplinary care and education of athletes, coaches, and healthcare professionals play a key role in the prevention and management of RED-S.