Taking Action with Antioxidants

April 2003

The National Academy of Sciences (NAS) defines a dietary antioxidant as a substance in foods that significantly decreases the adverse effects of reactive species, such as reactive oxygen and nitrogen, on normal physiological function in humans. This definition was based on several criteria: the substance is found in human diets, the content of the substance has been measured in foods commonly consumed, and the substance decreases the adverse effects of reactive species in vivo in humans.

Included in the 2000 NAS report on antioxidants, vitamin C (the RDA is 90 mg for males and 75 mg for females), vitamin E (the RDA is 15 mg for both males and females) and selenium (the RDA is 55 µg for males and females) meet these specifications. However, beta-carotene and other carotenoids influence biochemical reactions that involve the oxidative process, although they do not meet the definition. Some of the other antioxidants in the news are glutathione, coenzyme Q10, lipoic acid, flavonoids, phenols and phytoestrogens.

Much research on chronic disease has focused on the damage to cells caused by high levels of reactive oxygen and nitrogen species. This damage to DNA, proteins and lipids can contribute to cellular dysfunction and disease. Antioxidants can stabilize free radicals before they harm the body.

Epidemiological studies have found a strong association between a diet high in fruits and vegetables and a decreased risk for chronic diseases, such as cardiovascular disease and cancer. In addition, studies have aimed at investigating the role of diets high in fruits and vegetables and specific antioxidants in age-related diseases, such as cataracts, age-related macular degeneration (AMD), and central neurodegenerative diseases, such as Alzheimer’s and Parkinson’s.

Cardiovascular disease
One factor in reducing the risk of cardiovascular disease is antioxidants’ ability to protect LDL cholesterol from oxidation. In a recent statement on optimal diets for the prevention of coronary heart disease (CHD) — Journal of the American Medical Association, Nov. 27, 2002: 2569-2578 — Frank B. Hu and Walter C. Willett identified dietary changes that most effectively prevent CHD. In their opinion, evidence from metabolic studies, prospective cohort studies and clinical trials indicates at least three dietary strategies that are effective in preventing CHD, two directly linked to antioxidant intake: increasing consumption of omega-3 fatty acids from fish, fish-oil supplements or plant sources, and consuming a diet high in fruits, vegetables, nuts and whole grains, and low in refined grain products. They note that the effect of individual phytochemicals, antioxidants, vitamins and minerals remains unsettled.

Cancer fighters
DNA damage is a common thread in the development of cancerous cells. Antioxidants help protect cells from DNA damage and block the formation of carcinogenic compounds. For years, the public has heard that eating a variety of fruits and vegetables decreases the risk of developing many types of cancer. And when specific antioxidants were studied, it became evident that there was much more going on than seeing protective effects with targeted antioxidant supplementation. In fact, when results were released from several studies with beta-carotene and cancer that found an increased risk of lung cancer for smokers taking the supplement for four to eight years, many researchers and health professionals began to rethink specific antioxidant supplementation.

Some foods that have gained attention because of their antioxidant status are prunes; raisins; berries; citrus fruits; dark, green leafy vegetables, such as kale and spinach; Brussels sprouts; broccoli; peppers; tea; whole grains; and honey. A review (Journal of Agricultural & Food Chemistry, 2002, 50:6910-6916) looked at antioxidants in 10 common vegetables based on U.S. consumption per-capita data. Based on the proposed bioactivity index (BI) for dietary cancer prevention, it ranked them in the following order (from highest to lowest): spinach, red pepper, broccoli, cabbage, carrot, onion, celery, potato, lettuce and cucumber. The BI for dietary cancer prevention was proposed to provide a simple reference for consumers to choose vegetables on the basis of their beneficial activities.

Herbal answers
A review of the antioxidant activity and phenolic compounds in selected herbs (Journal of Agricultural & Food Chemistry, 2001, 49:5165-5170) determined that the diversity and complexity of the natural mixtures of phenolic compounds in the various herb extracts makes it difficult to characterize every compound and assess or compare their antioxidant activities. However, the authors note that the total phenolic contents and oxygen radical absorbance capacity (ORAC) values were higher than those reported for berries, fruits and vegetables. This study reinforced that herbs are an effective source of natural antioxidants.

Looking forward, just where is antioxidant research headed? According to Brent Flickinger, research scientist, Archer Daniels Midland Company (ADM), Decatur, IL: “I believe the research is going to focus on mixtures of antioxidants as well as mixtures of tocopherols in the case of vitamin E. I believe it will also focus on dose and duration of antioxidant mixtures, and the big research areas continue to be cardiovascular disease, diabetes and cancer.”

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