Ascorbic Acid Beyond Antioxidant Activity: Redox Modulation, Pharmacokinetics and Clinical Interpretation

Abstract Vitamin C (ascorbic acid) is traditionally described as an antioxidant micronutrient; however, this characterization only partially captures its biological complexity. Beyond direct radical scavenging, ascorbic acid acts as a functional modulator of redox-sensitive enzymatic systems, influences cellular signaling, and participates in the regulation of key metabolic and immune processes. This critical narrative review examines vitamin C through an integrated lens encompassing pharmacokinetics, redox biology, and clinical interpretation. Particular attention is given to the non-linear relationship between oral intake, plasma concentrations, and tissue exposure, as well as to the biological non-equivalence between oral and intravenous administration. Evidence from physiological, preventive, and clinical settings is discussed with emphasis on baseline nutritional status, exposure profiles, endpoint selection, and contextual factors that may account for heterogeneous study outcomes. Rather than framing vitamin C as a therapeutic agent, this review proposes a framework in which its effects are interpreted as context-dependent support of physiological processes, clarifying both its potential relevance and its intrinsic limitations in clinical research and practice.