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Research & Technical Articles
Antioxidants (continued)
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Vitamin C Revived
Vitamin C is currently America's most popular antioxidant supplement. Millions of us take daily doses well above the recommended daily allowance (RDA) of 60 mg-with no known side effects (probably because the body eliminates excesses).
Indeed, research has shown doses between one to six grams a day may lessen both the symptoms – and duration – of colds (Journal of the American College of Nutrition, 1995). (This study "overturns" two decades of research that disputed two-time Nobel-Laureate Linus Pauling's claim that megadoses of C are safe and can reduce the symptoms of colds.)
Beta Carotene Blues
Of the three major antioxidants, it is perhaps beta carotene that has received the most critical media attention. Concerns first surfaced in 1994, when a six-year-long research project from Finland linked supplemental beta carotene taken by cigarette smokers to a higher risk of lung cancer.
Then earlier this year, the National Cancer Institute (NCI) developed similar concerns about beta carotene supplementation.
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Like the Finnish study, the NCI's Beta Carotene and Retinol Efficacy Trial (CARET) was designed to explore the influence of beta carotene (and vitamin A) as preventive agents for lung cancer in high-risk men and women (i.e., heavy smokers and asbestos workers). But four years into the study, investigators terminated the study, believing the beta carotene supplements may actually be doing harm.
Another NCI study, the 12-year Physician's Health Study (PHS), which examined 22,000, mostly non-smoking, male physicians who were taking beta carotene every other day, showed neither benefit nor harm from beta carotene supplementation.
In response to this inconclusive research, the National Institutes of Health (NIH) eliminated beta carotene supplements from its ongoing 10-year Women's Health Initiative research project-a clinical trial of 40,000 female health professionals designed to measure the impact of dietary changes on breast cancer, colorectal cancer, and coronary heart disease. However, the study will continue to evaluate every-other-day doses of 600 IUs (international units) of vitamin E (and 100 mg of aspirin or placebos).
Although the results of these studies provide no conclusive evidence of harm-or benefit from beta carotene supplements-until we know more, the NCI and other national organizations, such as the American Heart Association (AHA), are urging us to get our antioxidants only from the foods we eat, while others are modifying their beta carotene recommendations.
"The epidemiological studies have shown that populations that consume higher levels of plant foods-fruits, vegetables, and grain products-have a reduced risk of several types of cancer," offers Carolyn Clifford, PhD, chief of NCI's Diet and Cancer Branch.
Andrew Nicholson, MD, director of preventive medicine at the Physicians' Committee for Responsible Medicine, also believes the goal is for people to eat a healthful, plant-based diet, rich in fruits and vegetables; supplements should not substitute for a healthy diet.
Says Dr. Mitchell: "Although the Finnish and NCI studies were well-designed, they were done with skewed populations [that included smokers and perhaps others with an unhealthy lifestyle]. Results from ongoing quality studies are needed before we can draw conclusions for non-smokers. Unfortunately, we're not going to have information about these results for another five or 10 years."
> Antioxidants continued
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