New antioxidant vitamin RDAs better, but not good enough

April 09, 2000

The increases announced today for the recommended dietary allowances of antioxidants such as vitamins C and E are a step in the right direction, experts say, but still fall short of the amounts that many studies have shown could help prevent heart disease, stroke and cancer.

For the first time in a decade, the Food and Nutrition Board of the National Academy of Sciences has increased the recommended daily amounts of certain antioxidant micronutrients: vitamin C from 60 milligrams per day to 90 for men, 75 for women; and vitamin E from 10 milligrams per day for men and eight for women to 15 for both men and women. The RDA for selenium remained unchanged at 55 micrograms for women, but dropped from 70 to 55 micrograms for men.

"Going into this review, the goal was to identify levels of these micronutrients that would help prevent chronic disease, not just the amount needed to prevent deficiencies such as scurvy for vitamin C, or peripheral neuropathy for vitamin E," said Balz Frei, professor and director of the Linus Pauling Institute at Oregon State University.

"But I'd have to say the final report recommendations, although encouraging, don't go far enough," Frei said. "These levels are once again about what it takes to prevent deficiency symptoms, not the amounts that could clearly help us in the fight against cancer, heart disease, stroke and other chronic health problems."

Both clinical and epidemiological studies by numerous researchers provide a wealth of evidence, Frei said, that higher levels of dietary antioxidants could help in the battle against the biggest health threats in America today. But the Food and Nutrition Board panel making these recommendations apparently did not feel this body of evidence constituted proof, he said, and they opted to make very limited changes.

Frei testified twice before the panel and helped review some of the reports. OSU colleague Maret Traber, an associate professor in the Linus Pauling Institute, was a member of the panel and helped draft the section on vitamin E. Both researchers say more could have been done.

Based on its own research and that of other scientists around the world, the Linus Pauling Institute recommends a combination of diet and supplements that will provide about 200 milligrams a day of vitamin C, 200 milligrams of natural vitamin E (also called d-alpha-tocopherol), and 200 micrograms of selenium, which it calls the "200 rule." About 120 milligrams a day of vitamin C is probably adequate to help prevent heart disease and cancer in young, healthy adults, Frei said, and would have been a more defensible choice for an RDA level. Considerably larger doses than that may be required to maintain optimal levels in older adults and treat disease, he said.

The issue with vitamin E is even more pronounced. The old standard was 8-10 milligrams and the new one is 15 milligrams; but the amount most likely to be of value in reducing the risk of heart disease and other chronic diseases is about 200 milligrams, the OSU experts say.

"The actual vitamin E consumed by American adults is about eight milligrams a day," Traber said. "It isn't clear whether chronic diseases such as heart disease and cancer are a hallmark of these long-term, sub-optimal vitamin E intakes. But higher intakes of vitamin E may be beneficial if chronic diseases such as heart disease, stroke, cancer, diabetes, and Alzheimer's disease result in part from sub-optimal protection by antioxidants."

The amount of vitamin E that had beneficial effects in epidemiological studies, Traber said, was more than 100 milligrams per day -- an amount not achievable by normal dietary means, but easy to provide by inexpensive supplements. And the new report did confirm that natural vitamin E is about twice as potent as its synthetic counterpart.

There is a persuasive body of evidence supporting their recommendations, the Pauling Institute scientists say. It includes:

A review of over 200 research articles on the health benefits of vitamin C suggests that intake of at least 100 milligrams a day is associated with a reduced incidence of and mortality from heart disease, stroke and cancer.

Even higher intakes of vitamin C may be required to reduce the risk of cataracts.

Over 20 clinical studies have shown that daily doses of 500 milligrams of vitamin C or more can significantly improve the relaxation of blood vessels in humans; impaired blood vessel relaxation is a significant risk factor in angina pectoris, heart attacks and stroke.

A daily dose of 500 milligrams of vitamin C can reduce blood pressure in patients with mild to moderate hypertension, another important risk factor in cardiovascular disease.

A study of 970 U.S. men supplemented with 200 micrograms of selenium daily for four years showed they had a 63 percent reduction in the incidence of prostate cancer, as well as a significantly reduced incidence of colon and lung cancer.

The reduction of heart attack risk by vitamin E supplements is likely due to the ability of vitamin E to interfere with platelet aggregation and prevent blood clots.

"There simply is a great deal of evidence that moderately higher levels of these antioxidants are not going to hurt you, and they are very likely going to help," Frei said. "Heart disease, stroke and cancer are the three top killers in the U.S., causing about 1.3 million deaths per year. The potential of adequate vitamin C, vitamin E and selenium to benefit public health and reduce the economic and medical costs associated with these diseases is substantial."

The diet situation in the U.S. and many other nations, Frei said, is not good. About 20 percent of the public already fails to get enough vitamin C, he said, and the numbers are much worse for vitamin E and the elderly. And raising the standards will only increase the number of people who "officially" have inadequate nutrition.

"However, these rdas are important, and should be taken seriously," Frei said. "They are the basis for foods in our school lunch programs, the military, food programs for the elderly, and supplements added to many of our processed foods. And people believe in them. That's why it's important to get these minimum standards set at levels that reflect the best science and current studies. I don't believe the changes made today accomplish that goal."

Oregon State University

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