Determination of activity of antioxidants in human subjects

Evidence from biochemical and animal models suggests that nutritional antio xidants should inhibit the development of diseases such as CHD and certain cancers. This evidence is not clearly corroborated by intervention studies in human subjects, due, in part, to inadequacies in current analytical meth odologies. Although in vitro assays can give useful information on the attr ibutes required by a compound to act as an antioxidant, results may have li ttle nutritional relevance due to limited bioavailability. The determinatio n of antioxidants in blood is often used as a measure of antioxidant status in vivo, but may not necessarily reflect concentrations in target tissues where oxidative stress is greatest. In addition, the accumulation of antiox idants in selective tissues may not be apparent from plasma measurements. P articipation in quality-control schemes for antioxidant determination by HP LC allows inter-laboratory comparison of results. Moderation of indices of oxidative damage to lipids, proteins and DNA can provide information on the effectiveness of compounds as nutritional antioxidants. However, most curr ent methods of assessing oxidative stress are subject to confounding factor s of non-oxidative origin. Assays for total antioxidant capacity in plasma differ in their type of oxidation source, target and measurement used to de tect the oxidized product. They give different results, should never be use d in isolation, and results should be interpreted with caution. Until more is known about the activity and metabolic fate of antioxidants, caution sho uld be exercised in the consumption of large amounts of commercially-availa ble antioxidant preparations.