Oxygen free radicals and correspondent defence mechanisms in humans

摘要

Oxygen free radicals (OFR) are produced as by-products of normal metabolic pathways of the biological oxidation of fat, carbohydrates and proteins. Enhanced generation of OFR takes place under pathophysiological conditions such as oxidative stress, acute infections, burns, chronic inflammatory and degenerative disorders. As a consequence of enhanced metabolic activity an imbalance of the oxidant-antioxidant systems may occur. Across the human lifespan there are periods at which such an imbalance due to a lack of trace elements and/or vitamins is more likely to develop than in others. Data available suggest that these periods comprise the second half of the first year, the second and third year of life and the time of puberty. In elderly people an imbalance may occur due to impaired antioxidant systems as a result of dietary choices. Diseases affecting the digestive tract including, among others, coeliac disease, cystic fibrosis and persistent diarrhoea, may cause an imbalance by impairing the antioxidant screen through malabsorption of vitamins such as vitamin E and provitamin A, and trace elements such as selenium and zinc. Concerning biomarkers, serum selenium concentrations < 45 μg/L are regarded to be an indicator of an oxidant-antioxidant imbalance in favor of the former.