Potential Role of Oral Nitrate Bioactivation in Interindividual Exercise Responses to Dietary Nitrate: A Narrative Review

Background: Equivalent doses of dietary nitrate often yield highly heterogeneous exercise responses across individuals. Efficient enterosalivary nitrate-to-nitrite conversion is dependent on oral commensal bacteria, representing a critical upstream step that may drive downstream variability in biomarker profiles and exercise outcomes. This review evaluates whether variation at the oral bioactivation step helps account for differences in downstream biomarkers and exercise performance. Methods: We conducted a structured narrative review of PubMed and Web of Science covering 1 January 2006 to 31 March 2026 using predefined keywords related to dietary nitrate, oral bioactivation, oral microbiota, enterosalivary pathway, and exercise performance. Human supplementation trials, antibacterial mouthwash perturbation studies, investigations evaluating oral function, and supporting case-report and preclinical evidence were included when they linked nitrate exposure, oral microbial activity or salivary nitrite kinetics, and physiological or exercise performance outcomes. Results: Oral bacteria are essential contributors to efficient enterosalivary nitrate-to-nitrite conversion. Associations between oral function and nitrite availability, as well as selected physiological measures, are reasonably consistent. However, direct evidence linking oral function to athlete performance remains sparse. No athlete trial identified in the present search has concurrently measured oral function, tracked serial nitrate/nitrite kinetics, and paired these data with a reliable performance test and prespecified mediation analysis. A rise in salivary nitrite therefore confirms engagement of the enterosalivary pathway, but it does not reliably identify an ergogenic responder. Current evidence does not yet allow quantitative estimation of how much between-person performance variability is attributable to oral bioactivation. Conclusions: Oral nitrate-reducing function remains a biologically plausible modifier of exercise responses, but it is not a validated predictive biomarker. Integrated athlete trials are needed to trace the full pathway from nitrate exposure to performance outcomes and to quantify within-person and between-person variation.