So should we be taking vitamin supplements?
A pretty simple question to answer, one might think. After all, there have been literally thousands of studies on how vitamin and mineral intakes relate to health. More than 100 million people in North America believe the question has been answered and take a variety of daily supplements to protect themselves against disease, spending some $25 billion in the process. But could they be on the wrong track?
The role of supplements
There are several ways to investigate the potential role of supplements. Surveys can identify those people who take supplements and make correlations to their health status. Alternatively, researchers can measure blood levels of specific antioxidants and relate the finding to disease patterns. Or they can carry out intervention studies in which results are evaluated after subjects take either the substance being tested or a placebo over an extended period. Finally, a "meta-analysis" can be undertaken in which the results of various high-quality studies are pooled to reveal information that is not apparent from looking at single studies.
A typical survey-type, or "observational," study involved over 83,000 healthy American physicians who filled out questionnaires about supplement intake and dietary habits. Roughly 30 percent of the doctors regularly took vitamin supplements. After about six years, 1,000 or so had died of some form of cardiovascular disease. Were the deceased more or less likely to have been taking antioxidant supplements? As it turned out, there was no relationship between supplement intake and cardiovascular death.
Of course, it is possible that physicians are more health conscious that others and pay more attention to their diet, so that they already had a sufficient intake of antioxidants. Some studies have even shown a negative supplement effect. Analysis of data collected from some 70,000 postmenopausal nurses showed that over an 18-year period, those who consumed the most vitamin A from food or from supplements had the greatest risk of bone fractures. On the other hand, low vitamin E intake during pregnancy has shown to increase the risk of childhood asthma, and women who take vitamin supplements during pregnancy appear to have a reduced risk of having infants who develop brain tumours.
How about studies of blood levels of vitamins? English researchers in one case found that among 20,000 people, those who had the highest level of vitamin C in the blood lived the longest. But was this because of the vitamin C, or was the vitamin C just acting as a marker for increased fruit and vegetable intake? Low levels of folic acid have been linked with breast cancer, heart disease and, most significantly, with giving birth to babies with neural tube defects. Still, such studies do not show cause and effect. You can never be certain that the observations are not due to some other dietary factor that happens to parallel folic acid in its presence. That's why intervention studies are the most meaningful. And in the case of folic acid in pregnant women, they certainly back up the observational studies. Supplementing the diet with 400 micrograms of folic acid daily significantly reduces the risk of neural tube defect.
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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. What do antioxidants do?
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.
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.
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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. Supplements proved not helpful
Dr. Bjelakovic decided to look into this possibility by mounting a second meta-analysis. His team tracked hundreds of published trials on the health effects of beta-carotene, vitamin A, vitamin C, vitamin E and selenium supplements, and whittled these down to 68 that met the criteria for proper blinded, randomized, placebo-controlled trials. Some studies used low doses of supplements, some high; some lasted months, other many years. Some used single antioxidants, others used various combinations. But the strength of a anti-meta-analysis lies in pooling results from many studies, evening out variables and allowing an overall conclusion to emerge. As in his previous study, Bjelakovic found no benefit from the supplements, and as before, he noted an increase in mortality among supplement takers. The data appear to be robust. More than 230,000 participants were involved in the 68 trials, 21 of which focused on healthy subjects who were taking antioxidants to prevent disease.
No surprise, the salvo of criticism has been furious. Many relevant trials were excluded, critics claim. Causes of death were not determined and may have had nothing to do with supplements. Subjects took numerous other supplements and prescription drugs that could have clouded the issue. There is no biological mechanism that can explain potential harm by antioxidants. Well, that one is not exactly true. Certain white blood cells, for example, attack toxins by generating free radicals, and it is possible that antioxidants can interfere with this activity. No doubt, some of the criticism aimed at the Bjelakovic analysis is valid, but given that so many subjects and so many studies were involved, any significant benefit from the antioxidants examined would have become apparent. Incidentally, Dr. Bjelakovic and his group received no funding from any commercial enterprise and appear to have no reason to either knock or support dietary supplements.
Better to get our vitamins from food than from pills
While I do not think that vitamin supplements are killing us, there is mounting evidence that it is better to get our vitamins from food than from pills. It seems that there is an almost magical blend of antioxidants, minerals and probably unrecognized other ingredients in fruits, vegetables and whole grains that cannot be replicated in supplements. A 13-member expert panel of the National Institutes of Health in the United States concluded that there is insufficient evidence for or against recommending vitamin supplements except in three cases. Supplementation with B vitamins in women of child-bearing age is beneficial, as is supplementation with calcium and vitamin D in postmenopausal women to prevent bone fractures. And the progression of macular degeneration can be reduced with a mix of beta-carotene, zinc, vitamin C and vitamin E. Note that taking supplements to prevent heart disease is not one of the recommendations. That may surprise many people because it has become almost dogma that certain vitamin and mineral supplements can prevent hardening of the arteries (atherosclerosis), which can lead to heart disease.
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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. Multivitamins and their effect on atherosclerosis
There is no doubt that, in the test tube, antioxidants such as vitamins E and C, the vitamin A precursor beta-carotene, and the mineral selenium can reduce the free-radical damage that plays a role in the development of atherosclerosis. The B vitamins also have been presumed to have a protective effect because they are an important factor in lowering the levels of homocysteine in the blood, an independent cardiovascular disease risk factor. As we have already seen, studies of human populations have shown that higher concentrations of homocysteine are associated with an increased risk of heart disease. And many researchers have noted that populations with a low dietary intake of antioxidant vitamins show greater progression of atherosclerosis. Such observations, however, cannot prove cause and effect. People who have low antioxidant intake probably have numerous other lifestyle differences as well.
Proving cause and effect requires randomized controlled trials in which supplements are given to one group, and a placebo to another. So far, as we have seen, such clinical trials have not shown a major protective effect in terms of preventing the symptoms of heart disease. But there is always the lingering possibility that the trials have not been long enough.
That is exactly why researchers at Johns Hopkins Hospital in Baltimore decided to investigate whether supplements can slow the process leading to atherosclerosis, by peeking directly into the human body. These days there are a number of imaging techniques, including angiograms, ultrasound, MRI and CAT scans that can actually document the extent of hardening of the arteries. Dr. Eliseo Guallar and colleagues identified 11 randomized, controlled trials that involved giving patients antioxidant supplements or B vitamins and that monitored the status of their coronary arteries. Two of the antioxidants trials used only vitamin E; three used a combination of vitamin E and C; and the others used various combinations of vitamins E and C, beta-carotene and selenium. Several trials used only the B vitamins. In other words, all of the supplement methodologies that had been promoted to reduce cardiac risk were explored. The results were very disappointing. None of the vitamin combinations reduced the progression of atherosclerosis. Furthermore, the vitamins had no effect on preventing the closure of coronary arteries that had been opened up by balloon angioplasty. Based on the thorough evaluation of these well-controlled studies, the Johns Hopkins researchers conclude that the widespread use of vitamin-mineral supplements to prevent atherosclerosis is not supported by the scientific evidence.
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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. Multivitamins and prostate cancer
In spite of a lack of scientific support, many people take supplement as "nutritional insurance," just in case their diet is inadequate. There is no great risk here and possibly even some benefit as long as mega-doses are avoided. This is underlined by a National Cancer Institute study published in 2007 that showed a link between excessive use of multivitamin supplements (more that one multivitamin a day) and an increased risk of advanced prostate cancer. There was no problem with men who took just one daily multivitamin; in fact, there seemed to be a slightly protective effect against the disease.
So where does this leave us?
The scientific consensus is that vitamin C in the 250 to 500 milligram range is safe enough, as is vitamin E in doses up to 400 IU. Vitamin A should not exceed 4,000 IU, and it is preferable if some of this comes from beta-carotene, its precursor. The best case for supplementation can be made for vitamin D and the B vitamins, particularly folic acid. We have seen the tantalizing data linking vitamin D with protection against various cancers and the studies that suggest the risk of dementia is reduced with adequate B vitamin intake. Supplements containing about 2 milligrams of vitamin B6, 6 micrograms of B12 and 400 micrograms of folic acid can compensate for a lack of these in the diet. As far as vitamin D goes, many researchers now believe that we should be getting about 1,000 IU a day, an amount that is hard to achieve without supplements.
Although vitamin purveyors often clamour about their products being of higher quality than others, differences between the major brands have no particular significance. Often, the same manufacturer produces vitamins for various distributors, which are then sold at varying prices. While the actual value of taking vitamin supplements is questionable, there is no doubt that for many people they provide comfort and hope, which may be valuable at any price.
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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.