It is reasonable to expect that antioxidants such as vitamins E or C, or the vitamin A precursor, beta-carotene, should play a role in preventing heart disease. Why? Because it is well known that cholesterol is most likely to damage coronary arteries when it is oxidized, in other words, when its molecular structure is slightly altered by reaction with oxygen. Antioxidants, in theory, should counter this effect. But in practice the story seems to be different.
Researchers in Oxford, England, enrolled over 20,000 adults with heart disease risk factors such as diabetes, high blood pressure or high blood cholesterol in a major study. Half received a daily supplement of 600 IU vitamin E, 250 milligrams vitamin C and 20 milligrams beta-carotene, while the others got a placebo. The supplements were certainly effective in increasing blood levels of vitamins, as tests clearly showed. But after five years there was absolutely no difference in any form of disease or in death rates between the groups. Maybe, though, these subjects already had the beginnings of cardiovascular disease that could not be reversed with the supplements and perhaps in a healthy group, supplements can prevent disease. Maybe …
To supplement or not?
As is evident, it is possible to support either side of the "to supplement or not" debate by looking at the scientific literature selectively. But what happens when scientists put all the data together in a meta-analysis? Sometimes they just add to the confusion! That's what Goran Bjelakovic and his colleagues at the University of Nis in Serbia and Montenegro apparently did when they examined the relationship between dietary antioxidants and the risk of gastrointestinal cancers. Free radicals can form in the gut and have been implicated in cancer, and fruits and vegetables have been shown to be protective, presumably because of the antioxidant content. So it certainly seemed reasonable to expect that antioxidant supplements should be beneficial in preventing cancer. Bjelakovic scoured the scientific literature and identified 14 rigorous placebo-controlled trials involving over 170,000 subjects. All the trials used oral supplements, although amounts varied, as did combinations. Vitamin C ranged from 120 to 2,000 milligrams a day, vitamin A from 1.5 to 15 milligrams, beta-carotene from 15 to 50 milligrams, selenium from 50 to 228 micrograms and vitamin E from 30 to 600 IU. The supplements were taken for years, either daily or every other day. Such doses are typical of what average consumers might take.
Shocking results
The results of the meta-analysis were unexpected. No protection against esophageal, gastric, colorectal, pancreatic or liver cancer was found. Selenium supplementation in a few of the trials did show some optimistic results. Now for the real shocker: in seven trials, all of high quality, involving over 130,000 subjects, the supplement takers had a higher rate of premature death! The researchers actually calculated that one premature death would be expected for every 100 people taking supplements. Little wonder that this work prompted sensational headlines like "Vitamins Only Take You Closer To Death." How do we interpret this surprising finding? The study was well executed and has statistical weight, but is it not possible that people who are ill are more likely to take supplements and that this explains the increased mortality? Or that supplements are most effective when taken for longer periods? And maybe they don't protect against cancer but have other benefits.
Excerpted from An Apple a Day: The Myths, Misconceptions and Outright Exaggerations about Diet, Nutrition and the Foods We Eat. Published by HarperCollins Publishers Ltd. Copyright 2007 by Dr. Joe Schwarcz. All rights reserved. Reprinted by permission of HarperCollins Publishers Ltd.
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