Free radicals are produced as a by-product of normal cell metabolism, such as when our bodies covert food into energy. They can also enter our bodies from exposure to tobacco smoke, pollution, and radiation from the sun and x-rays. When free radicals build up in cells, damage to DNA can occur. Damage to cellular DNA has been linked to the development of cancer and cardiovascular disease. Additionally, certain age-related disease, such as Alzheimer’s and Parkinson’s disease, may also be influenced by free radical-induced damage. By neutralizing free radicals, antioxidants are believed to provide protection against the development or progression of these diseases. It should be noted, however, that free radicals also participate in some health-promoting activities, such as killing germs while assisting with wound healing.
Antioxidants and cancer: While the general perception among the public is that antioxidants are beneficial, research into the effect of antioxidants on cancer has been mixed. The National Cancer Institute summarized the results of the major research into the effect of beta-carotene and other antioxidants in cancer prevention as follows:
- The first large randomized trial on antioxidants and cancer risk was the Chinese Cancer Prevention Study, published in 1993. This trial investigated the effect of a combination of beta-carotene, vitamin E, and selenium on cancer in healthy Chinese men and women at high risk for gastric cancer. The study showed a combination of beta-carotene, vitamin E, and selenium significantly reduced the incidence of both gastric cancer and cancer overall.
- A 1994 cancer prevention study entitled the Alpha-Tocopherol (vitamin E)/ Beta-Carotene Cancer Prevention Study (ATBC) demonstrated that lung cancer rates of Finnish male smokers increased significantly with beta-carotene and were not affected by vitamin E.
- Another 1994 study, the Beta-Carotene and Retinol (vitamin A) Efficacy Trial (CARET), also demonstrated a possible increase in lung cancer associated with antioxidants.
- The 1996 Physicians’ Health Study found no change in cancer rates associated with beta-carotene and aspirin taken by U.S. male physicians.
- The 1999 Women’s Health Study (WHS) tested effects of vitamin E and beta-carotene in the prevention of cancer and cardiovascular disease among women age 45 years or older. Among apparently healthy women, there was no benefit or harm from beta-carotene supplementation. Investigation of the effect of vitamin E is ongoing.
Antioxidants and Cardiovascular Disease: Free radicals, acting on low-density lipoproteins (bad cholesterol), has been considered a leading cause of atherosclerosis (the development of fatty buildup in the arteries). Over time, atherosclerosis can lead to heart attacks and strokes. Clinical trials have been conducted to determine if antioxidants could prevent damage to the vessels and the development of cardiovascular disease.
As with the studies evaluating the effect of antioxidants on cancer, the results of research looking at the benefits of antioxidants in treating or preventing cardiovascular disease has not been conclusive. A review of the literature published in the journal of the American Heart Association found:
- Ten studies that showed no effect of taking antioxidants (vitamin E, vitamin C, and/or beta-carotene) on cardiovascular disease events (e.g. heart attack).
- Five studies that demonstrated a protective effect against the development of heart attacks in patients with known heart disease or increased heart attack risk when taking antioxidants (vitamin E and/or vitamin C)
- Five studies that showed an increased risk of adverse effects (e.g. stroke, progression of arterial blockage, and death from all causes) in the study group that took various antioxidants.
The conclusions drawn by the authors of this review of the literature was that “the existing scientific database does not justify routine use of antioxidant supplements for the prevention and treatment of cardiovascular disease.”
While there are a number of theoretical benefits to taking antioxidants, current research has yet to provide convincing evidence of their effectiveness. A few of the reasons for this include the specific antioxidant (or its dosage) that was being tested, the source of the antioxidant (supplements vs. food), and the specific type of disease that was being studied. Nevertheless, because of the potential benefits, many authorities continue to advise that people take antioxidants and in next week’s Health Tip, we’ll look at some of the best sources.
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