Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: TUESDAY, April 26, 1994 TAG: 9404270008
SECTION: EXTRA PAGE: 1 EDITION: METRO
SOURCE: Jane Brody
DATELINE: LENGTH: Long
As if that were not distressing enough, the study also suggested that some harm might result from daily supplements of beta carotene, which was previously considered harmless in megadoses many times higher than those needed to prevent nutritional deficiencies.
Smokers who took 20 milligrams of beta carotene each day developed 18 percent more lung cancers than those who were given vitamin E or a dummy pill, and those who took 50 milligrams a day of vitamin E had a slightly higher rate (which was not statistically significant) of hemorrhagic stroke.
The study was conducted among 29,000 men initially aged 50 to 69 who were randomly assigned to take different vitamin regimens.
It has been widely hailed as the most carefully designed investigation in people into the presumed protective role of supplements of antioxidant nutrients.
It was especially welcomed by the Food and Drug Administration, which is now trying to stop an effort by the vitamin industry to make health claims on supplement labels and to distribute studies that support the claims to consumers even if other research contradicts the studies.
But did the study prove that such supplements were useless or harmful either for smokers or, more importantly, for the vast majority of people who do not smoke but who are otherwise exposed to countless substances that can cause oxidative damage to their genes or cells?
A new finding should never be accepted at its face value without an attempt to evaluate it in the context of other studies. When this is done for the Finnish study, it becomes apparent that no definite conclusion can be reached at this time as to the benefit or harm of the supplements studied for smokers or for anyone.
Several factors are worth considering.
First, does the finding make biological sense? Antioxidants - specifically vitamins E and C and beta carotene - have been found in numerous studies to slow, block or reverse harmful oxidative changes in body substances and cells.
For example, vitamin E helps to block oxidation that converts LDL cholesterol from a form that stays in the blood to a form that can stick to and clog arteries. And beta carotene has been shown to reverse precancerous changes in cells that line the mouth and cervix.
Neither in animal studies nor in human studies has a toxic effect of either nutrient been noted, and the Finnish researchers were unable to explain the higher lung cancer rate among those who took beta carotene.
But some laboratory evidence suggests that when antioxidants like beta carotene reach very high levels in blood and tissues, they can cause oxidation instead of preventing it. Such levels are reached when people take a high-dose supplement but not when they eat ordinary carotene-rich foods.
Second, does the finding mesh with research observations among large groups of people? These so-called epidemiological studies can never prove cause and effect.
They can only show an association between two factors that may indeed result from a direct link between them or that may, on the other hand, simply suggest that another associated factor is the real cause of the observed result.
Two major epidemiological studies involving 120,000 people, smokers and nonsmokers, found a significant reduction in heart disease among men and women who took large daily supplements of vitamin E, and one study of 22,000 male doctors showed a similar benefit from taking 50 milligrams of beta carotene every other day for 10 years.
As for anticancer effects, at least 17 studies in people have found that those whose diets are richest in carotenoids have the lowest risk of developing lung cancer.
Beta carotene is the most prominent, but hardly the only, carotenoid in the American diet. Another group of studies links diets rich in carotenoids to protection against stroke and heart attack.
As with all epidemiological studies, these do not prove that vitamin E, beta carotene or carotenoids in general are protective. The findings may mean that people who choose to take such supplements or eat a carotenoid-rich diet also have other characteristics that are the real source of protection.
Or the failure of the Finnish study to note a benefit from taking supplements of beta carotene could mean that something else in carotene-rich foods - other carotenoids, dietary fiber, various cancer-blocking chemicals like sulphoraphane, recently isolated in broccoli, or something not yet discovered - confers the observed benefit.
Third, was the new study designed in a way that would give a meaningful answer to the research question?
If the question was whether taking a beta carotene supplement or a small dose of vitamin E for six years can block the lung damage caused by 36 years of smoking an average of a pack of cigarettes a day, then, yes, the study answers this: the supplements were not effective.
But if you want to know whether, as a smoker or non-smoker, you might benefit from or be harmed by taking beta carotene or a large dose of vitamin E for decades, the study cannot help you.
With regard to vitamin E, the dosage used in the study may account for its failure to note a benefit. Study participants were given a daily dose of only 50 milligrams (international units) of a synthetic form of vitamin E that is not well absorbed and that raises blood levels of the vitamin by only one-third.
The vitamin E dose used in studies that showed a beneficial effect, by comparison, is hundreds of milligrams, which doubles blood levels of the vitamin.
As for beta carotene, if this nutrient confers its anti-cancer effect early in the cancer process, then taking it for a short time after decades of heavy smoking would be useless against a disease like lung cancer, which may take 20 years or more to develop.
Only a much longer study begun early in people's smoking careers could conceivably reveal a benefit.
In an editorial accompanying the Finnish report in The New England Journal of Medicine, researchers from Boston and Oxford, England, said the results ``do not disprove the potential benefits of antioxidant vitamins, but they do provide timely support for skepticism and for a moratorium on unsubstantiated health claims.''
In other words, further careful research is needed before any conclusions can be drawn about benefits and risks of antioxidant supplements for smokers and others.
Other studies are already under way in women as well as in men, using higher doses taken for a longer time. Until they are completed, people have three options: They can change harmful habits like cigarette smoking, sedentary living and careless eating.
They can eat more foods rich in carotenoids and other protective substances, like carrots, cantaloupe, broccoli and other cabbage-family vegetables, spinach, collard greens, winter squash, apricots and sweet potatoes.
Or they can hedge their bets and, in addition to the first two options, also take supplements, particularly supplements of vitamin E, which is not readily available in a low-fat diet and cannot be obtained in any diet in the doses that are believed to protect the heart.
- The New York Times
by CNB