What Vitamins Should I Be Taking, Doctor?
Abstract & Commentary
In the past, physicians have been taught that healthy individuals can meet their vitamin requirements by eating a well-balanced diet. Nonetheless, nearly one third of the US population consumes some type of vitamin supplement on a regular basis.
Few randomized trials have been performed that compare a vitamin to a placebo for a specific clinical end point. Even when such trials have been completed they may be inconclusive because of the variability in the dietary intake of the study participants. While some of the trials have continued for several years, all are too short to answer specific questions regarding most chronic diseases, particularly those that occur only after a lifetime of experience.
Despite these shortcomings, it does appear that vitamin supplementation may be useful in certain select situations. Folic acid and its prevention of neural-tube defects when taken before and shortly after conception is the best studied. When such women are given 400 µg of folic acid on a daily basis, there is a 70% reduction in neural-tube defects.
Supplementing folic acid also might decrease cardiovascular disease and certain cancers, but the evidence is not conclusive. Because folate levels tend to be low in persons who regularly consume alcohol, supplementing folic acid in these individuals may be useful.
A considerable amount of information has been published that suggests vitamin E supplements may reduce the risk of coronary artery disease. However, its effectiveness in individuals who already have developed atherosclerosis is still open to question.
This paper also reviews the information known about vitamin B6 and vitamin B12. In individuals with normal diets they do not believe that it has been shown that supplementation of these vitamins is useful.
Humans synthesize vitamin D in response to exposure to the sun. For most individuals, sunlight exposure is sufficient. However, those who live in areas with reduced sunlight, or who do not go outside, may be vitamin D deficient. Milk (and a few other foods) is routinely fortified with this vitamin. It is not clear that huge amounts of vitamin D are safe.
Vitamin A theoretically could reduce cancer risk. However, up-to-date studies have failed to document a reduced risk in individuals who have taken vitamin A supplements. Large amounts of vitamin A during pregnancy increase the risk of birth defects.
Willett and Stampfer state that there is little evidence supporting the use of supplementary vitamin C beyond that which is acquired in a typical diet. They state that human tissues become saturated with vitamin C at low levels of intake.
Willett and Stampfer conclude that the use of a daily multivitamin supplement that does not exceed the recommended daily allowance of each vitamin has potential benefit and should not cause harm. They note that the cost of such multivitamins is extremely low. They also suggest that vitamin E supplementation might be useful for middle-aged and older Americans who are at risk for coronary artery disease. They also remind the reader that vitamin supplements cannot overcome the increased risk associated with "smoking, obesity, or inactivity" (Willett WC, Stampfer MJ. N Engl J Med. 2001;345:1819-1824).
Comment by Kenneth L. Noller, MD
This is one of the few times I have chosen to review an article that is not an original research paper. Because so many of our patients routinely ask about vitamin and mineral supplements (this article does not deal with minerals), I found this paper to be interesting and important—and as a bonus it is easy to read.
Increasingly over the past several years I have found that my patients (and my colleagues and myself) are taking multivitamins on a more regular basis, but they often take high doses. A number of retail chains have begun selling "megavitamins" for daily use. These are available with slightly different formulas for "active individuals," "postmenopausal women," "middle-aged men," and even "children." When you carefully read the labels of these "megavitamins" the doses are often 10 to several thousand-fold higher than the recommended daily allowance. These products are expensive and have not been shown to improve health.
Unfortunately, Willett and Stampfer did not address the "megavitamin" issue directly. I would have liked to see them discuss the risk (if any) of such vitamin regimens. Because the preparations vary so widely, it might have been unfair for them to make any blanket statements.
I do have 2 observations: First, since the vitamin industry is regulated poorly, we can never be certain that what is listed as being present in a given multivitamin is actually there. This is especially true for the off-brand bottles of individual supplements that are so widely sold.
Second, though many cancer patients suddenly begin taking huge doses of various vitamins, I have always wondered why that made any sense. Perhaps a vitamin could prevent cancer, but once a tumor is growing wouldn’t adding vitamins only increase the growth rate of the tumor? If vitamins are good for us aren’t they also good for tumors?
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