The '90s have been a good one for nutrition research.
Scientists have shown that doses of Vitamin C -- five or six times the recommended daily allowance, or RDA -- may slash the risk of several forms of cancer.
Doses of Vitamin E -- many times the RDA -- helps cuts the risk of heart disease.
Doubling the RDA for folic acid in reproductive-age women can dramatically reduce a certain type of birth defect.
And if teen-age girls consume lots more calcium, they might well avoid osteoporosis later in life.
All of which raises the question: What's wrong with the RDAs?
That minutiae-filled table of numbers and nutrients that was cast on paper almost 60 years ago is the subject of a lot of soul-searching among the people who set nutrition policy in the United States.
Almost everyone agrees that it's time to revamp the RDAs -- which is normally done about every five to 10 years, and was last done in 1989 -- but there is no money to fund the project and no consensus about how to do it should the money appear.
"The whole premise behind the RDAs is that at least every decade, we should take stock in what our research findings are," says Gail C. Frank, a nutrition professor at California State University, Long Beach. "These are not like the Ten Commandments and they never change. These are supposed to be evolutionary."
In the Washington-based offices of the Food and Nutrition Board, the branch of the National Academy of Sciences responsible for the RDAs, officials are pondering what would essentially be a revolutionary change in the document.
RDAs were established in 1941 at the request of the War 'D Department.
Military leaders wanted to know what to put in rations and how to beef up the many malnourished enlistees, says Allison Yates, executive director of the Food and Nutrition Board.
Eventually, use of the RDAs was expanded to reflect the amount of a nutrient needed to help all segments of the population avoid deficiencies.
Diseases such as rickets and scurvy began to fade.
But, says Ms. Yates: "For the last 20 years, more and more research has been devoted to the effects of nutrients on developing chronic diseases, such as cardiovascular disease and cancer. We need to think hard about how to (set RDAs) in the future as we get more sophisticated."
Many nutrition experts are eager to see a new set of RDAs that would have more impact on reducing the chronic diseases that kill so many Americans.
Nevertheless, there are nutritionists who fear that changing the RDAs to help prevent chronic disease will allow the document to be overtaken by special-interest groups and will lead consumers to falsely believe that they are not getting enough of certain nutrients.
For example, not everyone is at high risk of heart disease and, thus, would not need a drastic increase in Vitamin E, says Dr. Mark S. Meskin, director of the nutrition program at the University of Southern California School of Medicine.
"If you believe people with high levels of low-density lipoprotein cholesterol (a risk factor in heart disease) would benefit from extra Vitamin E, that's OK. But someone with low levels of low-density cholesterol doesn't need it. Incorporating higher levels in the RDAs is going to suggest that virtually everyone is deficient," he says.
Dr. Meskin says a better approach would be to leave the RDAs as they are and allow doctors and nutritionists to prescribe extra nutrients to high-risk people who might benefit from them.
"We shouldn't be micro-managing with the RDAs," he says. "The fact that there are therapeutic possibilities of many vitamins doesn't mean we should provide enough for every person for every therapeutic possibility."
Increasing the RDAs even for some groups -- the document lists the allowances for various age and gender groups -- might cause problems for other population groups, Dr. Meskin says.
For example, there is a concern over iron deficiency in women and children, which causes anemia. But about 10 percent of the population carries a gene that puts people at risk for iron overload. In one study, too much iron has been linked to heart disease, Dr. Meskin says.
"If we push supplements (with more iron) or fortified more foods with iron, we could actually see more cases of iron overload," he says. "Men, for most of their adult years, for example, don't need more iron."
Some nutritionists express concern that a dramatic increase in certain nutrient RDA levels might lead people to take supplements and ignore their overall diet.
The next RDAs may look at non-nutrient food components such as cholesterol, transfatty acids and phytoestrogens -- all components that have an effect on health.
It may also suggest how much of a nutrient can be obtained through food as compared to a supplement. Finally, it may create more categories for people older than 50.
Everyone agrees that hashing out new allowances under this format will be time-consuming and complicated.
"It's an extraordinarily complex process, and it becomes more complex with each go-around," USC's Dr. Meskin says. "I have a concern that it's becoming a very politicized document. Various nutrition groups stand to gain or lose depending on how they push the document. . . . The 10th edition (in 1989) came out very late because it had become a political football."