Vitamins and dietary supplements in cancer treatment: is there a need for increased usage?

Introduction: Vitamins are essential for homeostasis and proper functioning of organisms. These micronutrients prevent tumor onset by functioning as antioxidants and enzymatic cofactors involved in anti-stress and immune responses, modulating epigenetic regulators, and shaping the microbiota composition. Unbalanced diets and sedentary lifestyles contribute to obesity, associated with increasing cancer risk. Cancer patients often exhibit vitamin deficiencies due to chronic inflammation, anticancer therapies, and tumor-induced metabolic changes, leading to malnutrition and cachexia. Areas covered: This review critically analyzes preclinical and clinical studies, sourced from PubMed and ClinicalTrials.gov databases, that investigate the potential benefits of vitamin supplementation and dietary interventions, such as intermittent fasting and ketogenic diets, in mouse tumor models and cancer patients. This analysis elucidates the limitations of such interventions and suggests optimal dietary strategies to prevent cancer and enhance patients' quality of life and prognosis. Expert opinion: To date, clinical studies have found no substantial benefit of over-the-counter vitamin supplements and dietary interventions on cancer patients' health and prognosis. To prevent the spread of useless and potentially harmful products by the nutraceutical industry, establishing a regulatory authority is necessary to monitor and ensure product quality and validity before commercialization.