A Review of the Anticancer Effects of Vitamin C on Some Selected Cancers

Abstract

Vitamin C (ascorbic acid) has long been recognised for its antioxidant properties and contributions to human health, but only recently has it been seriously reconsidered as a therapeutic agent in oncology. This article aims to provide a comprehensive synthesis of recent peer-reviewed literature on the anticancer roles of vitamin C. Recent mechanistic, preclinical, and clinical studies have converged to reveal that vitamin C can exert selective pro-oxidative cytotoxicity in cancer cells, modulate epigenetic regulators, enhance immune surveillance, and interact synergistically with conventional chemotherapeutic agents and radiation therapy. High-dose intravenous vitamin C, in particular, achieves plasma levels unattainable via oral administration and generates cytotoxic hydrogen peroxide concentrations within the tumour microenvironment, selectively eliminating malignant cells while sparing normal tissues. Experimental findings illustrate that vitamin C can arrest cancer cell proliferation, induce apoptosis, and inhibit metastasis in a broad range of tumour types—including breast, colorectal, pancreatic, and lung cancers—especially in those with underlying Kirsten rat sarcoma viral oncogene homolog (KRAS) or BRAF mutations or epigenetic aberrations. Furthermore, vitamin C serves as a cofactor for TET enzymes and histone demethylases, reactivating silenced tumour suppressor genes and thereby promoting genomic stability. It also remodels the tumour microenvironment by strengthening extracellular matrix components and fostering anti-tumour immunity through enhanced infiltration and activity of cytotoxic lymphocytes. Epidemiological data suggest a consistent inverse relationship between dietary vitamin C intake and cancer incidence, notably for gastrointestinal and breast malignancies. Early-phase clinical trials demonstrate improved patient-reported outcomes, tolerable safety profiles, and potential enhancements in overall survival when vitamin C is administered as part of multimodal therapeutic regimens. Despite these advances, significant controversies persist. The bioavailability of oral versus intravenous vitamin C, patient selection criteria, the optimal timing and dosing protocols, and the interaction between vitamin C and cytotoxic therapies remain unresolved. Some studies report antagonistic interactions or negligible effects in randomised control settings, highlighting the heterogeneity in trial designs and patient populations. This review systematically integrates recent advances spanning molecular mechanisms, animal models, epidemiological studies, and clinical trials to provide a nuanced appraisal of vitamin C’s anticancer potential. It also outlines controversies, limitations, and the translational challenges of incorporating vitamin C into standard oncology practice, while offering recommendations for future research directions, including biomarker-driven patient stratification, combination therapies, and nanotechnology-based delivery systems. The growing evidence base warrants larger-scale clinical investigations, with the hope of establishing vitamin C as a safe, effective, and accessible adjunct in the treatment and prevention of cancer. In sum, the synthesis of current experimental, clinical, and epidemiological data underscores vitamin C’s diverse anticancer effects and its potential for integration into comprehensive, multimodal cancer therapies.