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OCR for page 163
A
Origin anc! Framework of the
Development of Dietary
Reference Intakes
This report is one of a series of publications resulting from the
comprehensive effort being undertaken by the Food and Nutrition
Boarcl's (FNB) Stancling Committee on the Scientific Evaluation of
Dietary Reference Intakes (DRI Committee) and its panels and sub-
committees.
ORIGIN
This initiative began in June 1993, when FNB organized a sympo-
sium and public hearing entitled, "Should the Recommended Dietary
Allowances Be Revised?" Shortly thereafter, to continue its collabo-
ration with the larger nutrition community on the future of the
Recommencleci Dietary Allowances (RDAs), FNB took two major
steps: (1) it prepared, published, and disseminated the concept
paper, "How Should the Recommencleci Dietary Allowances Be
Revised?" (IOM, 1994), which invited comments regarding the pro-
poseci concept, and (2) it held several symposia at nutrition-focuseci
professional meetings to discuss FNB's tentative plans and to receive
responses to the initial concept paper. Many aspects of the con-
ceptual framework of the DRIs came from the United Kingclom's
report, Dietary Reference Values for Food Energy and Nutrients for the
United Kingdom (COMA, 1991~.
163
OCR for page 164
164
DIETARY REFERENCE INTAKES
The five general conclusions presented in FNB's 1994 concept
paper were:
1. Sufficient new information has accumulated to support a reassess-
ment of the RDAs.
2. Where sufficient ciata for efficacy and safety exist, reduction in
the risk of chronic degenerative disease is a concept that should be
inclucleci in the formulation of future recommendations.
3. Upper levels of intake should be established where ciata exist
regarding risk of toxicity.
4. Components of food that may benefit health, although not
meeting the traditional concept of a nutrient, should be reviewoci,
and if acloquate ciata exist, reference intakes should be established.
5. Serious consideration must be given to developing a new for-
mat for presenting future recommendations.
Subsequent to the symposium and the release of the concept
paper, FNB held workshops at which invited experts discussed many
issues related to the development of nutrient-baseci reference values.
(FNB and DRI Committee members have continued to provide
updates and engage in discussions at professional meetings.) In
aciclition, FNB gave attention to the international uses of the earlier
RDAs and the expectation that the scientific review of nutrient
requirements should be similar for comparable populations.
Concurrently, Health Canada and Canaclian scientists were review-
ing the neeci for revision of the Recommended Nutrient Intakes (R:NIs)
(Health Canada, l990b). Consensus following a symposium for
Canadian scientists, cosponsored by the Canadian National Insti-
tute of Nutrition and Health Canada in April 1995, was that the
Canaclian government should pursue the extent to which involve-
ment with the developing FNB process would benefit both Canada
and the United States in leacling toward harmonization.
Baseci on extensive input and deliberations, FNB initiated action
to provide a framework for the development and possible inter-
national harmonization of nutrient-baseci recommendations that
would serve, where warranted, for all of North America. To this
end, in December 1995, FNB began a close collaboration with the
government of Canada and took action to establish the DRI Com-
mittee. It is hoped that representatives from Mexico will join in
future deliberations.
OCR for page 165
APPENDIX A
THE CHARGE TO THE COMMITTEE
165
In 1995, the DRI Committee was appointed to oversee and con-
cluct this project. It cleviseci a plan involving the work of seven or
more expert nutrient group panels and two overarching subcom-
mittees (Figure A-1) .
The Subcommittee on Interpretation and Uses of Dietary Refer-
ence Intakes (Uses Subcommittee), composed of experts in nutri-
tion, dietetics, statistics, nutritional epidemiology, public health,
economics, and consumer perspectives, was to (1) review the scientific
literature regarding the uses of clietary reference stanciarcis and their
applications, (2) provide guidance for the appropriate application
of DRIs for specific purposes and identify inappropriate applica-
tions, (3) provide guidance for adjustments to be macle for poten-
tial errors in clietary intake ciata and the assumptions regarding
intake and requirement distributions, (4) provide specific guidance
for use of DRI values for incliviclual nutrients, and (~) identify
research neecleci to improve the statistical underpinnings regarding
quantitative applications of the DRIs for assessing and planning
cliets for inclivicluals and for groups.
Standing Committee on the Scientific
Evaluation of Dietary Reference Intakes
Panels
Upper Reference
Levels Subcommittee
Ca, Vitamin D, Phosphorus, Mg, F
Folate, B12, Other ~ Vitamins, Choline
.
Vitamins C and E, Se, ,8-Carotene
and Other Carotenoids
Vitamins A and K, As, B. Cl, Cu. Fe, 12,
| Mn, Mo, Ni, Si, V, Zn l
Energy, Carbohydrate, Sugars, Fiber,
Fat, Fatty Acids, Cholesterol, Protein, and
Amino Acids l
Sodium, Chloride, Potassium,
Sulfate, Water
------------ I r
, Other Food
Components
Alcohol ~
1
FIGURE A-1 Dietary Reference Intakes project structure.
OCR for page 166
166
DIETARY REFERENCE INTAKES
This second report from the Uses Subcommittee examines the
appropriate uses of each of the DRI values in planning nutrient
intakes of groups and of inclivicluals; an earlier report presented
information on the appropriate uses of specific DRI values in assess-
ing cliets for groups and for inclivicluals (IOM, 2000a). Each report
presents the statistical underpinnings for the various uses of the
DRI values and also indicates when specific uses are inappropriate.
This report reflects the work of the DRI Committee, the Uses Sub-
committee, and the Subcommittee on Upper Reference Levels of
Nutrients.
ISSUES OF RELEVANCE FROM PAST DIETARY REFERENCE
INTAKE REPORTS
Methodo;togy to Develop Estimated Average Requirements and
Recommended Dietary A;~;towances When Requirements for Nutrients
Are Not Norma;l;ly Distributed
For most of the nutrients for which Estimated Average Require-
ments (EARs) have been established, the required assumption of
distribution of requirements is that of symmetry about the mean. In
the case of iron, a nutrient of concern in many subgroups in the
population in the United States, Canada, and other areas, require-
ments are known to follow a nonnormal distribution (IOM, 2001~.
Thus, a different method was neecleci to determine the intake of
iron at which half of the inclivicluals would be expected to be inacle-
quate in the criterion used to establish acloquacy (the EAR), and
also to construct an intake level at which only a small percentage of
the population would be inacloquate (the RDA). Similar adjustments
were macle for clietary protein (IOM, 2002a).
If the requirement of a nutrient is not normally clistributeci but
can be transformed to normality, its EAR and RDA can be estimated
by transforming the ciata, calculating the both and 97.5th percen-
tiles, and transforming these percentiles back into the original units.
In this case, the difference between the EAR and the RDA cannot
be used to obtain an estimate of the stanciarci deviation or the
coefficient of variation because skewing is usually present.
Where factorial modeling is used to estimate the distribution of
requirements from the distributions of the incliviclual components
of requirement, as was clone in the case of iron recommendations
(IOM, 2001), it is necessary to add the individual distributions (con-
volutions). This is easy to do given that the average requirement is
simply the sum of the averages of the individual component distri-
OCR for page 167
APPENDIX A
167
buttons , and a s tan ciarci deviation of the combine ci clistribu tion can
be estimated by stanciarci statistical techniques. The 97.5th percen-
tile can then be estimated (for a further elaboration of this method,
see Chapter 9 and Appendix I of Dietary Reference Intakes for Vitamin A,
Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese,
Molybdenum, Nickel, Silicon, Vanadium, and Zinc tIOM, 20014~.
If normality cannot be assumed for all of the components of
requirement, then Monte Carlo simulation is used for the summa-
tion of the components. This approach models the distributions of
the incliviclual components and randomly assigns values to a large
simulated population. The total requirement is then calculated for
each incliviclual and the meclian and the 97.5th percentile are calcu-
lateci directly. As was the case for iron (IOM, 2001), the underlying
joint distribution is approximated and a large number of inclivicluals
(100,000) are randomly generated. Information about the clistribu-
tion of values for the requirement components is mocleleci on the
basis of known physiology. Monte Carlo approaches may be used in
the simulation of the distribution of components, or where large
ciata sets exist for similar populations (ciata sets such as growth rates
in infants), estimates of relative variability may be transferred to the
component in the simulated population (Gentle, 1998~. At each
step the goal is to achieve distribution values for the component
that not only reflect known physiology or known direct observations,
but also can be transformed into a distribution that can be modeled
and used in selecting random members to contribute to the final
requirement distribution. When the final distribution representing
the convolution of components has been cleriveci, the meclian and
97.5th percentiles of the distribution can be directly estimated. It is
recognized that in its simplest form, the Monte Carlo approach
ignores possible correlation among components. In the case of iron,
however, expected correlation is built into the mocleling of require-
ment where components are linked to a common variable (e.g.,
growth rate) so that not all sources of correlation are neglected.
Life Stage Groups
Nutrient intake recommendations are expressed for 22 life stage
groups, as listed in Table A-1 and clescribeci in more detail else-
where (IOM, 1997~. If ciata are too sparse to distinguish differences
in requirements by life stage and gender, the analysis may be pre-
sented for a larger grouping. Differences are indicated by gender
when warranted by the ciata.
OCR for page 168
168
DIETARY REFERENCE INTAKES
TABLE A-1 The 22 Life Stage Groups for Which Dietary
Reference Intakes (DRIB) are Given
Life Stage Groups
Infants
0-6 mo
7-12 mo
Children
1-3 y
4-8 y
Males
9-13 y
14-18 `7
19-30
31-50 y
51-70 y
> 70y
Females
9-13 y
14-18 y
19-30 y
31-50 y
51-70 y
> 70y
Pregnancy
< 18 y
19-30 y
31-50 y
Lactation
< 18 y
19-30 y
31-50 y
NOTE: Differences in DRls are indicated by gender when warranted by the data.
Reference Heights and Weights Used in Extrapolating Dietary
Reference Intakes for Vitamins and E;tements
The most up-to-date ciata providing heights and weights of incli-
vicluals in the United States and Canada when the DRI process was
initiated in 1995 were anthropometric ciata from the 1988-1994
Third National Health and Nutrition Examination Survey
(NHANES III) in the United States, and older ciata from Canada.
Reference values cleriveci from the NHANES III ciata and used in
previous reports are given in Table A-2. The earlier values were
obtained as follows: the meclian heights for the life stage and gentler
groups through age 30 years were iclentifieci, and the meclian
weights for these heights were baseci on reported meclian Body Mass
Inclex (BMI) for the same inclivicluals. Since there is no evidence
that weight should change as adults age if activity is maintained, the
reference weights for adults age ci 19 through 30 years were applied
to all adult age groups.
The most recent nationally representative ciata available for Cana-
. .
dians (from the 1970-1972 Nutrition Canada Survey tDemirjian,
19804) were also reviewoci. In general, meclian heights of children
from 1 year of age in the United States were greater by 3 to 8 cm
(1 to 2.5 in) than those of children of the same age in Canada
measured two clecacles earlier (Demirjian, 1980~. This difference
could be partly explained by approximations necessary to compare
the two data sets, but more likely by a continuation of the secular
OCR for page 169
APPENDIX A
TABLE A-2 Reference Heights and Weights for Children and
Adults in the United States Used in the Vitamin and Element
Dietary Reference Intake Reportsa through 2001
169
Median Body Reference Reference
Mass Index Height, Weightb
Sex Age (kg/m2) cm (in) kg (lb)
Male, female 2-6 mo 64 (25) 7 (16)
7-12 mo 72 (28) 9 (20)
1-3 y 91 (36) 13 (29)
4-8 y 15.8 118 (46) 22 (48)
Male 9-13 y 18.5 147 (58) 40 (88)
14-18y 21.3 174 (68) 64 (142)
19-30 y 24.4 176 (69) 76 (166)
Female 9-13 y 18.3 148 (58) 40 (88)
14-18 y 21.3 163 (64) 57 (125)
19-30 y 22.8 163 (64) 61 (133)
a IOM (1997, 1998a, 2000b, 2001). Adapted from the Third National Health and
Nutrition Examination Survey, 1988-1994.
b Calculated from body mass index and height for ages 4 through 8 years and
older.
trenci of increased heights for age noted in the Nutrition Canada
Survey when it compared ciata from that survey with an earlier
(1953) national Canaclian survey (Pett and Ogilvie, 1956~.
Similarly, median weights beyond age 1 year derived from the
recent survey in the United States (NHANES III) were also greater
than those obtained from the older Canaclian survey (Demirjian,
1980~. Differences were greatest cluring adolescence, ranging from
10 to 17 percent higher. The differences probably reflect the secular
trenci of earlier onset of puberty (Herman-Giciclens et al., 1997),
rather than differences in populations. Calculations of BMI for
young adults (e.g., a meclian of 22.6 for Canaclian women com-
pareci to 22.8 for U.S. women) resulted in similar values, thus incli-
cating greater concordance between the two surveys by adulthood.
The reference weights used in the previous DRI reports (IOM,
1997, 1998a, 2000a, 2000b, 2001) were thus based on the most
recent ciata set available from either country, with recognition that
earlier surveys in Canada inclicateci shorter stature and lower weights
cluring adolescence than clici surveys in the United States.
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170
DIETARY REFERENCE INTAKES
New Reference Heights and Weights
As cliscusseci earlier, when the DRI process was undertaken in
1994, the references heights and weights used were clevelopeci baseci
on NHANES III ciata on BMI for children and young adults (IOM,
1997~. Given the increasing prevalence of overweight and obesity in
both adults and children (HHS, 1996), use of such population ciata
is of concern. However, recent ciata providing heights and ideal
BMIs for adults (Kuczmarski et al., 2000) and new growth charts for
infants and children have allowoci the development of new refer-
ence heights and weights (Table A-3) that should more closely ap-
proximate ideal weights baseci on low risk of chronic disease and
acloquate growth for children. These new values were used in the
DRI report published in 2002 (IOM, 2002a) and will be used in
subsequent DRI reports until they neeci to be revised baseci on new
ciata or because of a conceptual neeci.
TABLE A-3 New Reference Heights and Weights for Children
and Adults in the United States
Previous
Median New
Body Mass New Median New
Indexa Median Reference Reference
(BMI) BMIb Heightb Weights
Sex Age (kg/m2) (kg/m2) cm (in) kg (lb)
Male, female 2-6 mo 62 (24) 6 (13)
7-12 mo 71 (28) 9 (20)
1-3 y 86 (34) 12 (27)
4-8 y 15.8 15.3 115 (45) 20 (44)
Male 9-13 y 18.5 17.2 144 (57) 36 (79)
14-18 y 21.3 20.5 174 (68) 61 (134)
19-30 y 24.4 22.5 177 (70) 70 (154)
Female 9-13 y 18.3 17.4 144 (57) 37 (81)
14-18 y 21.3 20.4 163 (64) 54 (119)
19-30 y 22.8 21.5 163 (64) 57 (126)
a Taken from male and female median BMI and height-for-age data from the Third
National Health and Nutrition Examination Survey (NHANES III), 1988-1994; used in
earlier DRI reports (IOM 1997, 1998a, 2000b, 2001).
b Taken from new data on male and female median BMI and height-for-age data from
the Centers for Disease Control and Prevention/National Center for Health Statistics
Growth Charts (CDC/NCHS, 2000; Kuczmarski et al., 2000).
c Calculated from CDC/NCHS Growth Charts (CDC/NCHS, 2000; Kuczmarski et al.,
2000), median BMI and median height for ages 4 through 19 years.
Representative terms from entire chapter:
reference intakes
