Optimal Intake of Nutrients
Information that has emerged in recent years challenges our concepts of nutrient requirements. Although the details are still hazy, it is becoming increasingly clear that many substances have disease-preventing actions in ways that do not fit into the classic model of nutrientJdeficiency disease. In some cases, these substances are nutrients, notably vitamin E and selenium, but are apparently most effective at intakes far above what is required for preventing deficiency diseases. In other cases, the phytochemicals, there is no requirement, as the substances are not nutrients in the classic sense; possible examples of this are particular carotenoids and flavonoids by Weinberges and Heaney. Indicate that this concept applies to potassium and calcium by virtue of their hypotensive action. In a previous work, one of us (NT) argued that it is short sighted to define recommended nutrient intakes narrowly in terms of preventing deficiency diseases. For various nutrients, we can more accurately speak of three levels of intake.
A low intake is clearly deficient by any definition and will produce clinical symptoms or, at least, subclinical deficiency. A somewhat higher intake will prevent deficiency symptoms but will not fully protect health; it is best described as a suboptimal intake. A yet greater intake is required for maximal health preservation: an optimal intake. In the case of the phytochemicals, of course, we cannot talk of deficiency, although there does appear to be an optimal intake. Taking vitamin E as an example, a daily intake of under 5 mg is deficient, 10 mg (the US RDA) is suboptimal, whereas an optimal intake (assuming the previously cited evidence is correct) is between 50 and 500 mg. The reason for these different levels of requirement stems from the relationship between the nutrient or phytochemical and the cause of the disease. With classic deficiency diseases, such as scurvy, the disease is solely due to lack of the nutrient.
As a result, one or more specific biochemical pathways fail to operate normally. But with diseases prevented by relatively high doses of nutrients and phytochemicals, the true cause . a factor, such as tobacco, which the protective substances can counter to some extent. However, they typically do this in ways where the required dose is much higher than that pertaining to the prevention of a deficiency disease. Just as the discovery of the relationship
tween nutrients and deficiency diseases necessitated the establishment of the concept of recommended nutrient requirement, so the foregoing arguments suggest the necessity of a new concept based on optimal intake. In this regard, it matters little whether the substance question is a nutrient or not. Gey's proposed term, recommended optimum intake, closely rresponds to the aforementioned concept.
