Should the Recommended Dietary Allowances Be Revised?
Report of a recent scientific symposium
By Mary Clifford, RD
The National Academy of Sciences (NAS) in Washington, DC, was the site of a conference held this summer to decide the future of the Recommended Dietary Allowances (RDAs). The RDAs are levels of intake of essential nutrients, that on the basis of scientific knowledge, are judged by the Food and Nutrition Board of the NAS to be adequate to meet the known needs of practically all healthy persons.
Panels made up of both government and private sector representatives considered the limitations of the RDAs, and addressed whether or not concepts of chronic disease prevention should be included in future RDAs.
In the past, the RDAs have been revised about every 5 years. Since the most recent revision, (the 10th edition was published in 1989), there has been enough focus on new scientific evidence regarding nutrition that a factor in organizing the conference was to begin work on a new revision.
In an interview with VRG, Catherine Woteki, Ph.D., RD, Director of the Food and Nutrition Board of the NAS, stated "The question is, should [the RDAs] be revised now? Is there a sufficient body of new information that we need to revise them now?"
THE CURRENT SITUATION
Presently, the RDAs are intended for use mainly by professionals. The concept of
preventing chronic disease is only generally addressed. That area is intended to be
covered by the Dietary Guidelines, issued by the Department of Agriculture and the
Department of Health and Human Services. Those guidelines include more specific
health information, such as advice to limit fat and salt intake. Some industry
experts and others feel that combining the two documents may be of more use to both
health professionals and consumers.
CONSIDERING CHRONIC DISEASE
But the current situation may change. The develop-ment of a joint document is
currently under consideration, according to M.R.C. Greenwood, Ph.D, Chair of the
Food and Nutrition Board of the NAS.
Greenwood stated that while the RDAs originally focused on preventing deficiencies, "new information has caused us to look more at diet's role in chronic disease prevention."
She further posed the questions of whether or not the RDAs "should include a diet plan" and "qualitative statements about chronic disease prevention."
Discussion on these questions focused mainly on recent research linking antioxidant nutrients (vitamins A, C, and E) with heart disease, aging, and cancer.
Gladys Block, Ph.D, a professor at the School of Public Health, UC Berkeley, stated that, "The idea that we've been reflecting adequacy for long-term health based on the methods that we've been using is simply incorrect. Adequacy has to do with maintaining optimal or reasonably good health throughout the course of our lifetime. We haven't been using methods that are capable of detecting long-term health."
Block also feels that "known nutrient needs [are] exploding," and that a higher intake of antioxidant nutrients is warranted.
James Kirk, Ph.D, Senior Vice President of Research and Development at Campbell Institute of Research and Technology, agreed, stating that, "Consideration should be given to defining recommended intakes which not only prevent frank deficiencies, but reduce the risk of developing chronic diseases."
THE RDAs AND THE SUPPLEMENT INDUSTRY
Annette Dickinson, Ph.D, Technical Director, Council for Responsible Nutrition,
addressed the use of RDAs in supplement formulation. She cautioned that "for some
nutrients there may be no rationale for consumption of higher than RDA levels, while
for other nutrients, such as vitamin E, or vitamin C, there may be abundant
scientific support for intakes considerably in excess of and largely unrelated to
the RDA."
However, she went on to state that "my observation is that the vast majority of vitamin and mineral supplements on the market today are formulated largely without meaningful reliance on the RDAs."
Block's testimony focused largely on the antioxidant nutrients. She highlighted vitamin C as one example that may be too low in the current RDA, based partly on her calculations that "our primate ancestors may have gotten about 1000 mg a day."
Following the conference, VRG interviewed Block to get her views on whether a healthy diet alone can provide the increased levels of antioxidant nutrients to which she and several other speakers alluded.
Block replied that, "If you work at it, you can get 400-500 mg of vitamin C from the diet, and that may be enough. And you can get a good dose of carotenoids from the diet, and that may be enough. You can't get a high dose of vitamin E from the diet, and that may not be enough. I'm not against supplements."
ANTIOXIDANTS
Currently, vitamins A, C, and E are the most talked-about antioxidant nutrients.
They are thought to help prevent cancer, heart disease, and other degenerative
processes associated with aging. One theory as to why is that they prevent DNA
damage from the natural aging process. The concept of antioxidant nutrients has been
gaining in popularity. Early in 1992, the Vitamin Nutrition Information Service, an
arm of pharmaceutical company Hoffman-LaRoche, Inc., offered a conference called
"Beyond Deficiency: Vitamin Issues of the 90's." A number of respected scientists
and health professionals spoke on current nutrition issues. Not surprisingly,
antioxidants were on everyone's mind.
The consensus? Speaker after speaker noted the connection between antioxidants and disease. Harinder S. Garewal, MD, spoke on oral cancers, and noted, "Evidence from the last 20 to 30 years suggests that retinoids, carotenoids and antioxidant nutrients inhibit oral carcinogenesis."
Block, who also spoke at the NAS conference, discussed the "persuasive" evidence regarding vitamin C, carotenoids, and vitamin E in "the prevention of a variety of cancers."
Bruce Ames, Ph.D, Professor of Biochemistry and Molecular Biology at UC Berkeley, stated, "There is accumulating scientific evidence that vitamins, particularly antioxidants, may be important in the prevention of cancer, heart disease, and other degenerative disease." He added that antioxidants may also have additional roles which "may not be limited to preventing deficiency disease."
While all of this testimony may sound like a warning bell to start incorporating vitamin megadoses into your diet, consider the comments made by Julie Buring, D.SC, Associate Professor in the Department of Preventive Medicine at Harvard Medical School: "Antioxidant vitamins represent a promising — but as yet unproven — means to reduce risks of cardiovascular disease. More basic research is needed."
And most health professionals recognize already-proven methods to reduce our risk of chronic disease, including moderate fat intake, regular exercise, and adequate fiber intake, among other suggestions.
It's also important to remember that nutrition is an evolving science, and we are always discovering new substances in food that have protective effects against disease. It makes sense, therefore, to rely primarily on food for good health, for both its known nutrients and those we don't yet know exist.
USES AND LIMITATIONS OF THE RDAs
Assistant Surgeon General J. Michael McGinnis, MD, addressed shortcomings of the
present RDAs, and suggested that more than one set of recommendations may be called
for.
"The RDAs are recommended dietary allowances. The food label allowances we now use, the RDIs, are reference daily intakes. A reference and a recom-mendation serve two distinct purposes, yet traditionally, the public, encouraged by the nutrition com-munity, sees these two purposes as being essentially interchangeable."
McGinnis also went on to caution that, "We should bear in mind that if the RDAs are revised by setting significantly higher recommended levels to incorporate some concept of optimal nutrition, the apparent profiles of those very foods that form the basis for dietary recommendations will suffer. Fruits, vegetables, and whole grains, when compared against those higher recommendations, could look non-nutritious."
One of McGinnis' major concerns is that such comparisons would cause a decrease in consumption of those foods "that the scientific community now believes are epidemiologically linked with a reduced risk of significant chronic diseases." He also feels that the area of megadoses and safety issues needs additional scrutiny: "Overconsumption can pose hazards just as underconsumption can."
Kirk recommended that because of the increasingly global economy, the NAS should work with other agencies to develop consistent "international nutrition labeling standards...to mandate or ensure that food products carry consistent nutritional messages" from country to country.
Jan Lilja, Assistant Deputy Administrator at USDA, pointed out that the RDAs are used as the basis for a number of federal food programs, such as WIC and the National School Lunch Program, which serve millions of Americans.
"RDAs are an important tool for determining eligibility. With increased focus on reaching all those eligible for the WIC program, we are challenged."
She stated that presently, "The RDAs contain a margin of safety; they overestimate actual requirements for most people. Thus, it is hard to interpret when intakes below the RDA represent an individual health risk, and whether that health risk varies for sex and age groups."
The opportunity for public comment on the possible revision of the RDAs has passed. The next step in the process is a discussion of the testimony received at the conference by the Food and Nutrition Board. They will then draft an opinion paper in early 1994 to decide if the evidence indicates the need for an 11th edition of the RDAs.
Mary Clifford, R.D., is a nutrition advisor for The Vegetarian Resource Group. She is a practicing dietitian in Virginia.
Does Vitamin E Supplementation Reduce Coronary Artery Disease Risks?
Two large separate studies published in the May 20, 1993, New England Journal of Medicine suggest that vitamin E supplements of 100 to approximately 208 International Units per day taken over years may reduce the risk of coronary heart disease, the leading cause of death in the United States.
While the findings are very interesting, both studies had serious design flaws. Epidemiology studies are not randomized. A randomized study would have been better. Neither study had well defined information about cholesterol levels, another major risk factor for heart disease.
In my opinion, sufficient evidence does not exist based on these studies alone to recommend vitamin E supplementation. We simply don't know what possible risks may be discovered in people who take vitamin E supplements for years or decades. Better studies are now in progress which may answer these questions. - Jerome Marcus, M.D.
For further information see Rimm, Eric B. and others. Vitamin E Consumption and The Risk of Coronary Heart Disease in Men. N Engl J Med 328:1450-1456.
Stampfer, Meir J. and others. Vitamin E Consumption and the Risk of Coronary Heart Disease in Women. N Engl J Med 328:1444-1449.
