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Using criteria to establish nutrient intake values (NIVs)
Allison A. Yates
Abstract
One of the most important of the nutrient intake values
(NIVs) is the average nutrient requirement (ANR). The
ANR is defined as an intake value that will be adequate
for half of the individuals in a group of people with similar
characteristics. It is used to estimate the prevalence
of adequacy, and it serves as the basis for the individual
nutrient level (INL x ). The determination of adequacy is
a complex process, with the resulting value of the ANR
dependent on the criterion or functional outcome chosen
to define nutrient adequacy. Because nutrients have
multiple sites of action in human metabolism, it is possible
to demonstrate abnormal function in one parameter
measured or observed as a result of inadequate intake
of a nutrient, while other parameters requiring the
same nutrient appear normal or within normal ranges.
Thus, depending on the criterion of adequacy selected,
the requirement for a given nutrient may be at a lower
or a higher intake amount. In harmonizing development
of NIVs, it is important to clearly identify the
criterion of adequacy selected and the rationale for its
selection. Rarely are available data sufficient to provide
dose–response information from which to select a level
of intake at which half of the individuals demonstrate
adequacy and half appear to demonstrate inadequacy.
Three levels of intake, of which at least one level of intake
is below the requirement for most of the individuals in
the sample, and one level of intake is above their requirement,
are useful for establishing a level at which half of
the group might be considered to demonstrate adequacy.
Types of human nutrient studies that may be used to
obtain data are discussed, as well as characteristics of
the sample size needed to demonstrate adequacy. The
The author is affiliated with the Beltsville Human Nutrition
Research Center, US Department of Agriculture/Agricultural
Research Service, Beltsville, Maryland, USA.
Please direct queries to the author: Allison A. Yates, Director,
Beltsville Human Nutrition Research Center, USDA/ARS,
110300 Baltimore Ave., Beltsville, MD 20705, USA; e-mail:
Allison.Yates@ars.usda.gov.
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variation in requirements is also an important aspect in
predicting levels of intake that will have defined probabilities
of adequacy for groups (to develop the INL x ,
where x is the defined probability chosen). An analysis
of the origins of different types of variability is presented.
When estimating energy requirements, a special case of
NIVs, important issues must be considered. Additionally,
an example of evaluating data used to establish an ANR
for vitamin A, and the effect of variability in requirements
for vitamin A, is provided.
Key words: Average nutrient level, criterion of
adequacy, nutrient requirements, sample size
Introduction
The framework for nutrient intake values, as discussed
in this issue by King et al. [1], and the uses of quantitative
nutrient standards, as discussed by Murphy and
Vorster [2] and Vorster et al. [3], are well understood by
those who work in nutrition policy and program areas;
it is less well understood how human nutrition research
regarding nutrients and bioactive food components is
actually translated into establishing a nutrient intake
value, and whether such a reference value is a level of
intake thought to be adequate or a level thought to not
increase the risks associated with excess intakes. This
article outlines the steps in applying criteria to establish
nutrient intake values, describes the importance of
identifying and substantiating the criterion or criteria
selected to establish adequacy, and reviews how data
typically available are assembled and compared in the
process of establishing nutrient intake values.
Steps in applying criteria to establish nutrient
requirements
There are four general steps to determining nutrient
intake values (NIVs) based on scientific data where
nutrient intake has been estimated and various data
Food and Nutrition Bulletin, vol. 28, no. 1 (supplement) © 2007, The United Nations University.