Hydration and Nutritional Strategies for Endurance Exercise in the Heat: Differential Effects on Thermoregulation, Exertional Heat Illness Risk, and Performance — A Narrative Review

Background. Endurance exercise in the heat increases physiological strain and may contribute to exertional heat illness (EHI), but physiological, performance and clinical outcomes are often conflated. Aim. To compare hydration and nutritional strategies according to their effects on thermoregulation, direct EHI outcomes and endurance performance. Material and methods. PubMed/MEDLINE was searched through 8 October 2026. Human studies and evidence syntheses were reviewed narratively, with confidence judged separately for each intervention-outcome pair. Results. Euhydration and individualized drinking support fluid balance, while overdrinking increases exercise-associated hyponatraemia risk. Hyperhydration and internal cooling may provide small, context-dependent performance benefits; carbohydrate is primarily a fuelling strategy. Caffeine may slightly increase thermal strain, menthol mainly alters thermal sensation, and taurine remains experimental. Direct EHI-event evidence is scarce. One observational cohort associated a multicomponent cooling and fluid programme with fewer heat-related medical encounters but could not isolate individual effects. Conclusions. Strategies should be individualized, rehearsed and integrated with heat acclimation, pacing, environmental controls and emergency planning. Surrogate or performance benefits do not prove EHI prevention.