Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


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Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
PART I: APPLYING THE DIETARY REFERENCE INTAKES 45
mined) is relatively close to the AI or falls well below it. It follows from the
above discussion that individuals with intakes below the AI cannot be assessed
as having inadequate intakes. Although the proportion of a group with usual
intakes below the AI could be determined, great care should be taken to avoid
implying that this proportion does not meet their requirements (i.e., the AI
should not be used as a cut-point in the way that the EAR may be).
USING THE UL TO ASSESS A GROUP\u2019S NUTRIENT INTAKES
The UL can be used to estimate the proportion of a group with intakes above
the UL and, therefore, at potential risk of adverse health effects from excess
nutrient intake. The method for applying the UL is similar to the EAR cut-
BOX 3 Assessing Group Nutrient Intakes\u2014The RDA Is Inappropriate
The EAR for vitamin B6 for women aged 51\u201370 years is 1.3 mg /day and the RDA is 1.5
mg/day. Shown below is a distribution of dietary vitamin B6 intakes for a group of
women 51\u201370 years of age. The distribution has been adjusted for individual variability
using the method developed by the National Research Council. The data are from
NHANES III.
Selected Percentiles of Dietary Vitamin B6 Intake, Women 51-70 Years of Age,
NHANES III
Percentile 5th 10th 15th 25th 50th 75th 85th 90th 95th
Vitamin B6
intake
(mg/day) 0.92 1.02 1.11 1.24 1.51 1.90 2.13 2.31 2.65
Comparing the median intake of 1.51 mg/day to the RDA of 1.5 mg/day for this group
might lead one to believe that inadequate vitamin B6 intake is not a problem. However,
comparison of the distribution of usual intakes to the EAR cut-point shows that the
EAR value of 1.3 mg/day falls somewhere between the 25th percentile and the 50th
percentile of usual intakes. Thus, it can be concluded that greater than 25 percent of
usual intakes are below the EAR cut-point and the prevalence of inadequacy in this
group is estimated to be greater than 25 percent (but less than 50 percent).
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
46 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
point method in that the proportion of the group with intakes above the UL is
determined.
Because ULs for nutrients are based on different sources of intake, the ap-
propriate usual intake distribution must be used in the assessment. For some
nutrients, such as fluoride, phosphorus, and vitamin C, the distribution of usual
intakes would need to include intake from all sources. For others, such as mag-
nesium, folate, niacin, and vitamin E, only the distribution of usual intakes
from synthetic sources added to foods and from supplements (and in the case
of magnesium, medications) would be needed.
Another issue to consider when interpreting the proportion of a group
with intakes above the UL is that there is considerable uncertainty with regard
to some of the ULs for children. In many cases, these ULs were established
based on extrapolation from the ULs for adults or infants, and thus for some
nutrients, this resulted in very small margins or an overlap between the adult
RDA and the UL for young children. Surveys in the United States have revealed
that young children have a high prevalence of intakes above the UL for nutri-
ents such as vitamin A and zinc; however, few studies have been conducted in
children to assess the effects of such intakes.
USING THE AMDR TO ASSESS A GROUP\u2019S NUTRIENT INTAKE
By determining the proportion of the group that falls below, within, and above
the AMDR, it is possible to assess population adherence to the recommenda-
tions and to determine the proportion of the population that is outside the
range. If significant proportions of the population fall outside the range, con-
cern could be heightened for possible adverse consequences.
ASSESSING THE ENERGY ADEQUACY OF A GROUP\u2019S DIET
The probability approach and the EAR cut-point method do not work for as-
sessing energy adequacy. This is because empirical evidence indicates a strong
correlation between energy intake and energy requirement. This correlation
most likely reflects either the regulation of energy intake to meet needs or the
adjustment of energy expenditure to be consistent with intakes. Therefore, the
use of BMI as a biological indicator is preferable. The distribution of BMI within
a population group can be assessed, and the proportions of the group with
BMIs below, within, and above the desirable range would reflect the propor-
tions with inadequate, adequate, and excessive energy intakes.
How to Plan for the Nutrient Intakes of a Group
The goal of planning nutrient intakes for groups is to achieve usual intakes in
the group that meet the requirements of most individuals, but that are not
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Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
PART I: APPLYING THE DIETARY REFERENCE INTAKES 47
excessive. This can be challenging because the amount and selection of foods
that group individuals eat will vary, even if the same meal is offered. Situations
where group planning occurs include residential schools, prisons, military gar-
risons, hospitals, nursing homes, child nutrition programs, and food assistance
programs.
When planning for groups, a practitioner should aim for a low prevalence
of inadequate intakes. In the past, this may have involved considering the aver-
age intake of the group and comparing it with the RDA, which was inappropri-
ate because even if a group\u2019s average intake meets the RDA, the prevalence of
inadequacy is likely to be unacceptably high. This is because the variability in
nutrient intakes among group members usually exceeds the variability in the
requirements of group members, and it is the variability in requirements that is
used to set the RDA.
Instead, the new DRIs present an approach to planning that involves con-
sideration of the entire distribution of usual nutrient intakes within a group,
rather than just the average intake of the group. The goal is that the distribution
of usual nutrient intakes that results from the plan will have a low prevalence of
inadequate or excessive intake, as defined by the proportion of individuals in
the group with usual intakes less than the EAR or greater than the UL. An
important caveat: By focusing explicitly on the distribution of nutrient intakes
of a group as the goal of group planning, the framework presented here is, in
many respects, a new paradigm, and it should be tested before being imple-
mented in large-scale group-feeding situations.
To apply the framework presented here, an acceptable prevalence of inad-
equacy must be defined (a critical step on the part of the planner) and the
distribution of usual intakes in the group must be estimated. As previously
stated, this is accomplished by determining the distribution of reported or ob-
served intakes, and performing a statistical adjustment to estimate the distribu-
tion of usual intakes. A target (desired) usual intake distribution can then be
determined by positioning the distribution of usual intakes relative to the EAR
to achieve the desired prevalence of inadequacy.
Because the goal of planning is to achieve a target distribution of usual
intakes, assessment must occur (see \u201cProbability Approach\u201d and \u201cEAR Cut-Point
Method\u201d earlier in the chapter). In most cases, planning group intakes is an
ongoing process, in which planners set goals for usual intake,