08 May 2008

RDA system misses the mark

Regulating our nutrient intake is crucial, both from a benefit and risk perspective. But is the recommended dietary allowance (RDA) system our best tool? A US expert says no.

There is little doubt that excessive use of vitamins can be risky. In fact, in the last 23 years vitamin use is known to have directly accounted for the deaths of 10 people in the United States.

Of course, compared to pharmaceutical drugs, the risk is relatively low and it is clear that the dose ultimately makes the poison. It is here that guidelines on food and supplement labels play an important role in ensuring that consumers can track their nutrient intake.

But Prof John Hathcock*, vice-president of Scientific and International Affairs at the Council for Responsible Nutrition (CRN) in Washington, feels strongly about the fact that the widely accepted recommended dietary allowance (RDA) system is not a rational basis for setting maximums on products, and that the system is "outdated".

By voicing this concern at a recent press conference in Cape Town, Hathcock echoed a feeling that's been growing among dieticians and other experts in this country: RDA, which defines the intake that meets the basic nutrient needs of almost all (97-98%) individuals in a gender group at a given life stage, doesn't give an indication of the nutrient levels that will prevent chronic diseases of lifestyle (for example heart disease and cancer) and also doesn't give an indication of safety levels. Another limitation is that the system cannot be applied to substances without RDA values.

South African dieticians and other experts have been saying for some time now that the RDA system isn't sufficient and that recommendations for higher levels of nutrients would make more sense.

Safety is key
Instead Hathcock believes that there should be more emphasis on tolerable upper intake levels (UL) for daily intakes of nutrients instead of merely on the RDA values, and that these limits should be based on sound scientific evidence. The UL value of a nutrient (that is, the highest level of daily nutrient intake that is considered to be safe for almost all individuals of a specific gender and life stage) should then serve as a guideline of where to draw the line in terms of daily intake.

While this may sound somewhat risky, it's worth noting that the UL is not a threshold for toxicity. In other words, there is no known risk at the UL level, as the value is set within a wide safety margin. The UL is still well below the "no-observed-adverse-effect level" (NOAEL) and the "lowest-observed-adverse-effect level" (LOAEL).

"Consumers are often confused about what levels are appropriate for their needs," Hathcock says."The risk is not so much that consumers will take in too much of one nutrient, but rather that they are simply not aware of the doses."

He also believes that, in the absence of ULs, there is leeway for governments to set their own, arbitrary standards without scientific basis. This could possibly restrict fortification and could encourage sub-optimal nutrient intake, particularly with regards to disease prevention.

It's interesting to note that in South Africa, for example, a daily intake of more than 300mg vitamin C and more than 30 international units (IU) of vitamin E is considered "medicine". However, research shows that the UL of vitamin C is 2000mg and that of vitamin E 1000IU per day, highlighting the fact that South African legislation with regards to vitamins and minerals might well be outdated.

The RDA system also leads to disproportionate restriction of supplements in comparison with numerous conventional, unfortified foods. For example, a serving of beef liver may contain about 50 times the RDA for vitamin B12, while citrus fruits may contain two to three times the RDA for vitamin C.

Both RDA and UL on labels?
While Hathcock's argument to focus on ULs certainly makes sense, how this can be implemented in terms of South African labelling regulations is still unclear.

One thought is that indicating both the percentage RDA and the percentage UL value on food and supplement labels could be a start. The consumer's aim should then be to go for an intake that lies somewhere between the RDA and the UL, where the risk for deficiency as well as excess intake would be almost zero.

But the jury is still out on this one.

- (Carine van Rooyen, Health24, March 2008)

*Prof John Hathcock has more than 35 years of experience, including tenures as professor at Iowa State University and senior scientist at the Food and Drug Administration. He is expert on the application of quantitative risk assessment to the safety evaluation of nutrients and other dietary ingredients, and has made numerous presentations on safety of vitamins and minerals and other dietary ingredients to the US Food and Nutrition Board. He holds B.S. and M.S. degrees from North Carolina State University and the Ph.D. in nutrition from Cornell University.

Read more:
The vitamins you need


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