Antioxidants Uncovered

Dietary antioxidants are vitamins, minerals, carotenoids, polyphenols and other compounds found mostly in plant foods. Many antioxidants give foods their vibrant color, such as the deep-red of tomatoes and the blue-purple of blueberries. Antioxidants prevent free radicals from attacking cells and damaging DNA. Research suggests that free radicals are involved in the development of a number of degenerative diseases, including cancer, cardiovascular disease, cognitive impairment, Alzheimer’s disease, immune dysfunction, cataracts and macular degeneration.

In search of definition

Antioxidants are complicated. Some appear to confer health benefits and some do not, and some have mixed results. Remember the clinical intervention trial that revealed beta-carotene supplementation may be a contributing factor to increased risk of lung cancer in smokers?

Although many plant compounds have been loosely lumped together into the category of antioxidants, they are not interchangeable and differ from each other in sites and mechanisms of action. Some compounds can act as antioxidants under one condition and as pro-oxidants in another. It is unlikely that a common health benefit can be linked with each antioxidant. The Panel on Dietary Antioxidants and Related Compounds, Institute of Medicine (IOM), National Academy of Sciences (NAS), attempted to define dietary antioxidants in order to establish dietary reference intake levels (DRIs).

The panel developed a proposed definition of a dietary antioxidant as a substance in foods that significantly decreases the adverse effects of reactive oxygen species (ROS), reactive nitrogen species (RNS), or both, on normal physiological function in humans. The substance should be found in human diets, measured in foods commonly consumed, and must show, in humans, to decrease the adverse effects of free radicals.

Top four

Many compounds have been identified in foods that are potentially vital for health, but many lack enough solid research to back them up. Thus, the IOM panel narrowed its sights on beta-carotene and other carotenoids, vitamin C, vitamin E and selenium.

Beta-carotene, as well as other carotenoids like alpha-carotene, lycopene, lutein and zeaxanthin, and cryptoxanthin, are found in many fruits and vegetables. A large body of evidence links higher blood concentrations of beta-carotene and other carotenoids from foods with lower risk of several chronic diseases. But the IOM reported that the evidence cannot be used to establish a requirement for beta-carotene or carotenoid intake, because the effects may be due to other substances found in carotenoid-rich food or to other factors related to increased fruit and vegetable consumption.