Free radicals and antioxidants: Myths, facts and mysteries

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) are well recognized for playing a dual role as both deleterious and beneficial species. Overproduction of ROS arising either from mitochondrial electron transport chain or excessive stimulation of NAD(P)H oxidase results in oxidative stress, a deleterious process that can be an important mediator of damage to cell structures, including lipids and membranes, proteins and DNA. The powerful action of antioxidants in preventing premature lipid oxidation in food suggests that the same compounds, when consumed in the daily diet, could unfold anti-oxidative/anti-ageing effects in the human body. Failure of supplemental beta carotene to prevent cancer and cardiovascular diseases (CHD) in intervention trials, suggest that the associations of that nutrient, reflect confounding, rather than cause and effect results. The role of oxidative stress in diseases, especially cancer and CHD has been overstated. In the light of recent physiological studies, it appears more advisable to maintain the delicate internal redox balance of the cell than to interfere with the antioxidant homeostasis by a non-physiological, excessive exogenous supply of antioxidants in healthy humans.   Key words: Antioxidants, free radicals, Redox reactions, reactive oxygen species (ROS), reactive nitrogen species (RNS) and phytochemicals.