Vitamins are organic substances that we intake with our foods, and that act as biocatalysts, substances that help to trigger other reactions in the body. There are today at least three interesting scientific areas investigating the effects of vitamins and their results being implemented into the clinical medicine. They include trials of some vitamins' effects in treating antioxidant stress and in prevention of cardiovascular diseases. Another aspect important to general population is determination of daily intake of vitamins and the quality of nutrition (diet) regarding the health preservation. However, the antioxidant effects of vitamins are the most interesting for the contemporary human. Reactive oxygen species (ROS) are produced during different pathological processes in increased concentrations. They cause lipid peroxidation and oxidation of DNA and proteins due to their high chemical reactivity. However, antioxidative defense mechanisms, including different antioxidant enzymes and vitamins, prevent tissue damages and other ROS-related complications. In spite of often-controversial data of epidemiological and clinical studies, it seems that vitamin and mineral intake in doses equal or even higher than RDA not only benefits prevention of diseases related to their deficiency but also helps optimal development and upkeep of physiologic function and/or prevention of some degenerative diseases.