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Vitamin Facts

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By Brad Lemley, DrWeil.com News

To the dedicated supplement taker, it's a major disappointment to read the news stories - which seem to reappear every few years - stating that supplemental antioxidant vitamins don't reduce the risk of chronic disease. One high-profile example came on March 20, 2006, when Wall Street Journal writer Tara Parker-Pope weighed in with "The case against vitamins." The story contended that although an estimated 70 percent of American households purchase vitamins, several prestigious scientific organizations, including the Food and Nutrition Board of the National Academy of Sciences, have concluded that taking antioxidant vitamins - such as vitamins A, C and E - serves no purpose, and in some cases could even be harmful.

Yet at a conference called "Nutrition and Health: State of the Science & Clinical Applications" held in New York City in May, Jeffrey Blumberg, an antioxidant researcher from Tufts University, voiced a starkly opposing view of the vitamin facts. He said there is "strong and consistent" evidence that links higher intakes of antioxidant vitamins to lower risks of diseases including heart disease and cancer.

What's going on?

The key question, Blumberg said, is what constitutes "evidence." The studies that question the value of supplements included the ATBC Cancer Prevention Study from Finland, the Beta-Carotene and Retinol Efficacy Trial in the U.S. and the Vitamin A and Cancer Prevention Trial II in Australia. All were randomized clinical trials. News stories - and even medical journal articles - tend to focus on these as the final, definitive word in antioxidant research.

"Why are all of the conclusions about antioxidants based only on randomized clinical trials? It is because that is the dogma, that is the gold standard of evidence-based medicine today," Blumberg said. Since these trials have tended to show "null outcomes," he said, "it looks like there is no benefit."

But it makes sense, he said, to cast the net wider for more reliable vitamin facts. "We need to look at in vitro studies, animal-model studies, observational studies of individual patients in clinics or large scale populations within or between countries," all of which tend to show benefits of taking antioxidants, he said. "I simply don't think randomized clinical trials provide the only evidence."

The important thing to remember about randomized clinical trials of antioxidant vitamins, Blumberg said, is that they may not mimic real-world usage in several ways:

• The specific form of the vitamin used may be inferior. "In vitamin E studies, almost all of them have been done with the synthetic form of vitamin E, which is different from the natural source forms," he said.
• Studies often fail to find the truly susceptible population, which means the "controls" fare as well as the vitamin takers.
• The study may look too early or too late in the stage of the disease to find a benefit.
• There may be synergistic co-factors that were not included in the experiment. "Remember that clinical trials look at one dose, usually of only one antioxidant. In some of the most sophisticated trials, they use two antioxidants, and in on or two cases, three - vitamin C, vitamin E and beta carotene," Blumberg said.
• The dosage used may not be optimal.
• There may have been insufficient follow-up. "If you are trying to show that you can prevent cancer in a three or four year study, that's a real limitation."
• Poor compliance. In many of the studies, members of the placebo group began taking vitamins on their own, "reducing the difference between the two groups."
• Poor screening. Some subjects in, say, a vitamin E study might have natively high blood plasma levels of E because of diet, genetics or some other factor, he said. A well designed study would balance such people between the experimental and control groups. But in no study that Blumberg has evaluated has there been any prior screening of blood plasma vitamin concentrations.

Because of all of this, Blumberg said, it is far too soon to conclude that "antioxidant vitamins don't work."

Dr. Weil, who served as co-course director of the conference, agreed. "Vitamins, minerals and other supplements don't compensate for a bad diet, but they can fill nutritional gaps in a good one," he said. "The value of antioxidant vitamins has, in my view, been scientifically demonstrated beyond any reasonable doubt. Everyone should take a high-quality multivitamin daily."

What's the value of a multivitamin and antioxidant supplement in your diet? Find out with Dr. Weil's Vitamin Advisor.