Livro DRI 2006 (Micronutrientes)

Livro DRI 2006 (Micronutrientes)


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and also
by gender. The life stage groups were chosen by considering variations in the
requirements of all of the nutrients under review. If data were too limited to
distinguish different nutrient requirements by life stage or gender groups, the
analysis was then presented for a larger grouping.
INFANCY
Infancy covers the first 12 months of life and is divided into two 6-month
intervals. The first 6-month interval was not subdivided because intake is rela-
tively constant during this time. That is, as infants grow, they ingest more food;
however, on a body-weight basis their intake remains the same. During the
second 6 months of life, growth rate slows. As a result, total daily nutrient
needs on a body-weight basis may be less than those during the first 6 months
of life.
The average intake by full-term infants born to healthy, well-nourished
mothers and exclusively fed human milk has been adopted as the primary basis
for deriving the AI for most nutrients during the first 6 months of life. The only
exception to this criterion is vitamin D, which occurs in low concentrations in
human milk.
In general, special consideration was not given to possible variations in
physiological need during the first month after birth or to the intake variations
that result from differences in milk volume and nutrient concentration during
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
14 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
early lactation. Specific recommended intakes to meet the needs of formula-fed
infants have not been set.
\u2022 First 6 months (Ages 0 through 6 months): The AI for a nutrient for
infants in this age group was calculated using two measures, the average
concentration of the nutrient from 2 through 6 months of lactation and
an estimated average volume of human milk intake of 0.78 L/day. The
AI represents the product of these two measures. Infants are expected to
consume increasing volumes of human milk as they grow.
\u2022 Second 6 months (Ages 7 through 12 months): During this time, in-
fants experience slowed growth and gradual weaning to a mixed diet of
human milk and solid foods. There is no evidence for markedly differ-
ent nutrient needs, except for some nutrients such as iron and zinc,
which have relatively high requirements. An EAR and RDA for iron and
zinc have been derived for this age group. The AIs (again, with the ex-
ception of vitamin D) are based on the sum of the average amount of the
nutrient provided by 0.6 L/day of human milk and the average amount
of the nutrient provided by the usual intakes of complementary wean-
ing foods consumed by infants at this age.
TODDLERS: AGES 1 THROUGH 3 YEARS
Toddlers experience greater velocity of growth in height compared to 4- and 5-
year-olds, and this distinction provides the biological basis for establishing sepa-
rate recommended intakes for this age group. Data on which to base DRIs for
toddlers are sparse, and in many cases, DRIs were derived by extrapolating data
taken from the studies of infants or adults (see Appendix C).
EARLY CHILDHOOD: AGES 4 THROUGH 8 YEARS
Children aged 4 through 8 or 9 years (the latter depending on puberty onset in
each gender) undergo major changes in velocity of growth and endocrine sta-
tus. For many nutrients, a reasonable amount of data was available on nutrient
intake and various criteria for adequacy to serve as the basis for the EARs/RDAs
and AIs for this group. For nutrients that lack data on the requirements of
children, EARs and RDAs for children are based on extrapolations from adult
values.
PUBERTY/ADOLESCENCE: AGES 9 THROUGH 13 YEARS,
AND 14 THROUGH 18 YEARS
The adolescent years were divided into two categories because growth occurs
in some children as late as age 20 years. For some nutrients, different EARs/
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: INTRODUCTION TO THE DIETARY REFERENCE INTAKES 15
RDAs and AIs were derived for girls and boys. Several indicators support the
biological appropriateness of creating two adolescent age groups and gender
groups:
\u2022 Age 10 years as the mean age of onset of breast development for white
females in the United States; this is a physical marker for the beginning
of increased estrogen secretion (in African American girls, onset is about
a year earlier, for unknown reasons).
\u2022 The female growth spurt begins before the onset of breast development,
thereby supporting the grouping of 9 through 13 years.
\u2022 The mean age of onset of testicular development in males is 10.5 through
11 years.
\u2022 The male growth spurt begins 2 years after the start of testicular devel-
opment, thereby supporting the grouping of 14 through 18 years.
YOUNG ADULTHOOD AND MIDDLE AGE: AGES 19 THROUGH 30 YEARS,
AND 31 THROUGH 50 YEARS
Adulthood was divided into two age groups to account for the possible value of
achieving optimal genetic potential for peak bone mass with the consumption
of higher nutrient intakes during early adulthood rather than later in life. More-
over, mean energy expenditure decreases from ages 19 through 50 years, and
nutrient needs related to energy metabolism may also decrease.
ADULTHOOD AND OLDER ADULTS: AGES 51 THROUGH 70 YEARS,
AND OVER 70 YEARS
The age period of 51 through 70 years spans active work years for most adults.
After age 70, people of the same age increasingly display different levels of
physiological functioning and physical activity. Age-related declines in nutrient
absorption and kidney function also may occur.
PREGNANCY AND LACTATION
Nutrient recommendations are set for these life stages because of the many
unique changes in physiology and nutrition needs that occur during pregnancy
and lactation.
In setting EARs/RDAs and AIs, consideration was given to the following
factors:
\u2022 The needs of the fetus during pregnancy and the production of milk
during lactation
Copyright © National Academy of Sciences. All rights reserved.
Dietary Reference Intakes: The Essential Guide to Nutrient Requirements
http://www.nap.edu/catalog/11537.html
16 DRIs: THE ESSENTIAL GUIDE TO NUTRIENT REQUIREMENTS
\u2022 Adaptations to increased nutrient demand, such as increased absorp-
tion and greater conservation of many nutrients
\u2022 Net loss of nutrients due to physiological mechanisms, regardless of
intake, such as seen with calcium in lactation
Due to the last two factors, for some nutrients there may not be a basis for
setting EAR/RDA or AI values for pregnant or lactating women that differ from
the values set for other women of comparable age.
Reference Heights and Weights
Reference heights and weights for life stage and gender groups are useful when
more specificity about body size and nutrient requirements is needed than that
provided by life stage categories. For example, while an EAR may be developed
for 4- to 8-year-olds, it could be assumed that a 4-year-old girl small for her age
might require less than the EAR for her age group. Conversely, an 8-year-old
boy who is big for his age might require more than the EAR for his age group.
However, based on the model for establishing RDAs, the RDA (and AI) should
meet the needs of both.
There are other reasons for using reference heights and weights in deter-
mining requirements. Data regarding nutrient requirements that are reported
on a body-weight basis (such as with protein) necessitate the use of reference
heights and weights to transform the data for comparison purposes. Or, fre-
quently, the only available data are those regarding adult requirements. In these
situations, extrapolating the data on the basis of body weight or size is a pos-
sible