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PEDIATRICS Vol. 104 No. 1 July 1999, pp. 119-123
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ABSTRACT |
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Despite the American Academy of Pediatrics' (AAP) strong endorsement for breastfeeding, most infants in the United States are fed some infant formula by the time they are 2 months old. The AAP Committee on Nutrition has strongly advocated iron fortification of infant formulas since 1969 as a way of reducing the prevalence of iron-deficiency anemia and its attendant sequelae during the first year.1 The 1976 statement titled "Iron Supplementation for Infants" delineated the rationale for iron supplementation, proposed daily dosages of iron, and summarized potential sources of iron in the infant diet.2 In 1989, the AAP Committee on Nutrition published a statement that addressed the issue of iron-fortified infant formulas3 and concluded that there was no convincing contraindication to iron-supplemented formulas and that continued use of "low-iron" formulas posed an unacceptable risk for iron deficiency during infancy. The current statement represents a scientific update and synthesis of the 1976 and 1989 statements with recommendations about the use of iron-fortified and low-iron formulas in term infants.
At birth, most term infants have 75 mg of elemental iron
per kilogram of body weight, found primarily as hemoglobin (75%), but
also as storage (15%) and tissue protein iron (10%).4 Infants of mothers with poorly controlled diabetes and
small-for-gestational-age infants have approximately 10% and 40% of
normal storage iron, respectively, meaning that they may have less of a
buffer for protection from postnatal iron deficiency.5,6
During the first 4 postnatal months, excess fetal red blood cells break
down and the infant retains the iron. This iron is used, along with
dietary iron, to support the expansion of the red blood cell mass as
the infant grows. The estimated iron requirement of the term infant to
meet this demand and maintain adequate stores is 1 mg/kg per
day.1
Because more than 80% of the iron of the newborn term infant is
accreted during the third trimester of gestation, infants born before
term must accrete more iron postnatally to "catch up" to their term
counterparts during the first year. Thus, the requirements for preterm
infants range from 2 mg/kg per day for infants with birth weights
between 1500 and 2500 g2 to 4 mg/kg per day for
infants weighing less than 1500 g at birth.7 Preterm
infants who receive erythropoietin in lieu of red blood cell
transfusions appear to need at least 6 mg/kg per day of
iron.8
Daily iron dosing recommendations can only be estimates because they
represent the "supply side" of iron economics. Multiple postingestion variables alter the amount of metabolizable iron ultimately absorbed and retained by the infant. The greatest of these
factors is the percentage of iron absorbed from the diet. Estimates of
iron absorption from infant formulas range from less than 5% in term
infants fed casein-predominant formula to 40% in very low birth weight
infants fed whey-predominant formula.9-11 Values of 7%
to 12% appear to be most representative for term infants fed cow milk
formula, with the lower values seen when formulas supplemented with
higher concentrations of iron are used.11 The percentage
of iron absorbed from soy formula is lower than from cow milk formula
and ranges from less than 1% to 7%.12 Nevertheless,
infants fed soy formula containing 12 mg/L of iron remain comparably
iron sufficient to infants fed iron-fortified cow milk
formula.12
Factors such as the milk source of iron (eg, human vs cow), type of
iron compound consumed, the food with which it is eaten, and the iron
status of the infant greatly affect iron absorption. For example,
greater than 50% of iron from human milk is absorbed compared with
typically less than 12% of iron from cow milk-derived formula. In the
older infant, iron from meat sources and iron from ferrous sulfate is
better absorbed than iron from nonmeat sources or in its pyrophosphate
form. Infants with poorer iron status or in negative iron balance
absorb a higher percentage of dietary iron. Potential iron losses (such
as occult gastrointestinal bleeding associated with exposure to cow
milk protein or infectious agents) must also be considered. Larger
dietary doses will be necessary under those conditions to maintain iron
balance.
The American Academy of Pediatrics' Committee on Nutrition stated
more than a quarter century ago that "the early use of fortified formula results in augmentation of iron stores which help prevent later
development of iron deficiency."1 The strategy to
improve iron stores during the first year was a response to the high
rates of iron deficiency before the 1970s when the rate of cow milk
consumption during the first year and the concordant rate of iron
deficiency were unacceptably high. The strategy was designed to promote
at least neutral but preferably positive iron balance after 4 months of
age. The rationale for no net loss in iron balance is clear, because
humans have relatively low amounts of iron stores compared with total
body iron. Thus, there is a relatively small buffer zone to protect
developing tissues, such as the brain, heart, skeletal muscle, and
gastrointestinal tract, from iron deficiency.
The increased use of iron-fortified infant formulas from the early
1970s to the late 1980s has been a major public health policy success.
During the early 1970s, formulas were fortified with 10 mg/L to 12 mg/L
of iron in contrast with nonfortified formulas that contained less than
2 mg/L of iron. The rate of iron-deficiency anemia dropped dramatically
during that time from more than 20% to less than 3%.3,13
Nevertheless, low-iron formulas, defined by the US Food and
Drug Administration (FDA) as containing less than 6.7 mg/L of iron,
continue to be available and account for 9% to 30% of elective
(non-Women, Infants, and Children program) formula consumption in the
United States. Currently, most infants in the United States are not
breastfed beyond 3 months of age. Therefore, the number of infants who
could potentially receive low-iron formula (or cow milk) during late infancy remains high.
Although anemia is the endpoint of most studies of infant iron
supplementation, the physiologic deficits of iron deficiency are
apparently not attributable solely to the anemia. The onset of nonheme
tissue effects of iron deficiency predate the onset of anemia because
the body prioritizes iron for heme synthesis. When iron supply during
the first year does not meet the iron demand of the rapidly expanding
red blood cell mass, first iron stores in the liver and then nonstorage
iron in other tissues will be compromised.14 These changes
take place before any hematologic findings are evident. The nonheme
effects, thought to be attributable in part to reduction of
iron-containing cellular proteins, are responsible for many of the
clinical manifestations of iron deficiency. The combination of
hematologic and nonhematologic iron deficiency produces clinical
symptoms of weakness, muscle fatigue, abnormal gastrointestinal
motility, and, of most concern, permanent reduction of cognitive
ability.14,15
Because of the prioritization toward the hematopoietic system, many
infants consuming low-iron formula who have reduced iron stores or
frank tissue iron deficiency will not be given a diagnosis of iron
deficiency because they are not anemic when their hemoglobin is
routinely assayed at 9 months of age. Studies that assess the iron
storage capacity of the infant (serum ferritin) or the infant's compensatory response to reduced iron availability (increased iron
binding capacity) are not routinely performed during infancy. Thus,
early warning signs of negative iron balance are missed.
Infant formulas have been classified as low-iron or iron-fortified
based on whether they contain less or more than 6.7 mg/L of iron.
Nevertheless, traditional low-iron formula contains the amount of iron
inherent to the cow milk plus a small amount added for stabilization
during formulation. This results in iron concentrations of
approximately 1.1 mg/L to 1.5 mg/L of iron. Recently, one manufacturer increased the iron concentration of low-iron formula to 4.5 mg/L.
In contrast with low-iron formulas, iron-fortified formulas signified a
conscious attempt to "fortify" the infant's iron stores to protect
against the later development of iron deficiency. In the United States,
iron concentrations of iron-fortified formulas range from 10 mg/L to 12 mg/L. In Europe, infant formula tends to contain 4 mg/L to 7 mg/L of
iron.
Determining the acceptable range of iron concentration in infant
formula depends on what standard is used to assess iron sufficiency. The most common approach is to document the prevalence of iron deficiency in populations of infants fed formulas with various iron
concentrations with a target of ensuring that all infants are protected
from iron deficiency. Numerous studies have documented the unequivocal
reduction in iron deficiency (clinical and subclinical) in infants fed
iron-fortified vs low-iron formula.13,16,17 The rate of
iron deficiency anemia in 9-month-old infants fed formulas containing
1.1 mg/L of iron has ranged from 28% to 38%,16,17 even
when supplemental foods are consumed. This unacceptably high rate
decreases to 0.6% when formula fortified with 12 mg/L or 15 mg/L of
iron is used.16,17 Recently, Fomon et al18
demonstrated similar iron status in infants fed formula containing 8 mg/L or 12 mg/L of iron. Fewer studies have assessed the long-term
effect of intermediate formula iron concentrations (4 mg/L to 7 mg/L)
on iron status. Lonnerdal and Hernell19 recently reported
a trend toward higher ferritin concentrations and lower transferrin
receptor concentrations in infants fed a cow milk-based formula
containing 7 mg/L of iron compared with a group fed a formula
containing 4 mg/L. These data suggest that iron balance is stressed by
the formulas with lower iron concentration and that iron stores are
better in the more highly supplemented group, although there were no
differences in hemoglobin at the relatively early study endpoint of 6 months of age. There appeared to be no adverse effect on copper or zinc status in the more highly supplemented iron group.
Hokama20 estimated that breastfed 4- to 5-month-old
infants retain 0.06 mg/kg per day of iron from that source. Using 0.06 mg/kg per day of iron as a target accretion rate assumes that the
prevalence of iron deficiency in human milk-fed infants is acceptably
low. In studies in which infants were exclusively breastfed, the
prevalence of decreased iron stores appears to range between 6% and
20%,21,22 suggesting that this rate of daily iron
accretion may be near the lower borderline of promoting iron
sufficiency. Assuming a 12% absorption rate,11 an infant
consuming 130 mL/kg per day of low-iron cow milk formula containing 1.5 mg/L of iron would retain only 0.02 mg/kg of iron daily. Conversely,
even with an absorption rate as low as 7%, an infant consuming a
formula fortified with 12 mg/L of iron will retain 0.06 mg/kg of iron
per day.
A relatively small percentage of infants continues to be nourished
predominantly by formulas made at home by using evaporated milk as the
base and fortifying with additional sugar in the form of glucose
polymers. These formulas would have the same low-iron availability of
nonformula cow milk. Therefore, infants receiving these formulas should
receive exogenous iron supplementation from the time of birth to ensure
maintenance of iron storage pools as the infant grows.
The persistent use of low-iron formulas despite recommendations of
the American Academy of Pediatrics and multiple studies supporting the
use of iron-fortified formulas suggests that the reasons for continued
use may be multifactorial and largely nonmedical. Four issues appear to
influence physician-prescribing and consumer-buying practices: 1) the
perception that iron fortification causes gastrointestinal or
infectious problems, 2) the continued availability of low-iron products
to consumers, 3) the low-iron concentration of human milk, and 4) the
Infant Formula Act requirement that the phrase "with iron" be
prominently displayed on the front label of iron-fortified formula
containers.
There is a misconception by some health professionals and parents
that infants fed iron-fortified formulas have more gastrointestinal distress, such as colic, constipation, diarrhea, or gastroesophageal reflux. Of these, constipation and irritability appear to be the most
common concern. An association between iron and constipation is
appealing to mothers who remember the association between taking prenatal iron in large doses and changes in their own gastrointestinal tract function when they were pregnant.
A controlled study by Oski23 and a double-blind crossover
study by Nelson et al24 compared iron-fortified and
low-iron formulas and found no differences in prevalence of fussiness,
cramping, colic, gastroesophageal reflux, or flatulence. Moreover,
therapeutic iron up to 6 mg/kg per day given to infants is
well-tolerated.25
Although these studies are recognized by most pediatricians, dealing
with the fussy baby and the frustrated mother who is convinced that the
problem is due to iron in the formula remains difficult for some.
Parental education (particularly anticipatory guidance) is laudable,
yet it may remain temptingly easier to prescribe a low-iron formula,
achieve a placebo effect, and ignore the more insidious long-term
consequences of iron deficiency.
The low-iron formulas produced in the United States contain a
range of 1.5 mg/L to 4.5 mg/L of iron, well below the cutoff of 6.7 mg/L as defined by the FDA. All formula manufacturers in the United
States who produce low-iron formulas have attempted through their field
representatives to discourage the use of formulas that are deficient in
iron. Nevertheless, these formulas account for 9% to 30% of elective
infant formula sales in the United States. Manufacturers appear
reluctant to unilaterally discontinue providing a product for which
there is substantial consumer demand. This impasse is unlikely to be
resolved without a change in FDA regulations implemented in the Infant
Formula Act.
Some physicians rationalize the prescription of low-iron formula
by stating that the concentration of iron in human milk is approximately 20% of that found in low-iron cow milk formula (0.3 mg/L
vs 1.5 mg/L). Iron found in human milk is far more bioavailable, resulting in much lower rates of iron-deficiency anemia compared with
low-iron cow milk formula. Nevertheless, 6% to 20% of exclusively breastfed infants remain at risk for reduced iron
stores.21,22 A higher rate (20%-30%) of iron deficiency
has been reported in breastfed infants who were not exclusively
breastfed.17,21 The effect of iron obtained from formula
or beikost supplementation on the iron status of the breastfed infant
remains largely unknown and needs further study.
The Infant Formula Act required that formulas fortified with
greater than 6.7 mg/L of iron be labeled "with iron." Initially, this label was a positive message because iron fortification was considered desirable given the prevalence of iron deficiency in the
population. Over time, however, this type of labeling has come to
function as a reminder of the presence of iron in the formula, making
it a convenient scapegoat for the many aspects of infant formula
intolerance. No other nutrient, supplemented or in natural abundance,
in cow milk formula receives special consideration on the front label.
It may be appropriate to remove the term "with iron" from the front
label of the iron-fortified formulas. Instead, formulas with iron
concentrations that promote negative iron balance could be labeled as
"nutritionally incomplete," with a warning that "this formula is
not a complete diet for your infant because it lacks sufficient iron
and may lead to iron deficiency."
There are no known medical contraindications to using
iron-fortified formulas in formula-fed infants. In light of controlled studies,23,24 gastrointestinal symptoms are not an
indication for switching to a low-iron formula. The condition of the
rare infant with an iron overload syndrome can be carefully monitored.
However, the dose of iron received from human milk or infant formula is
minute in comparison with the total body iron load. Because these
infants undergo chelation therapy, the additional iron received from
infant formula that then needs to be chelated is negligible in
determining the chelator dose.
A theoretical concern has been raised about the use of iron-fortified
formulas as supplements for breastfed infants.26 The
proposed mechanism is that the higher iron content of iron-fortified formulas may saturate lactoferrin, a protein important in protecting the intestine from overgrowth with Escherichia coli. Infants
fed iron-fortified formula, partially breastfed infants supplemented with iron-fortified formula, and exclusively breastfed infants who
receive iron supplements may have a higher prevalence of E coli in the fecal flora compared with exclusively breastfed
infants who receive no iron supplementation. In the latter,
lactobacillus predominates.27 The physiologic significance
of this difference in flora with respect to diarrheal disease remains to be shown. A recent study demonstrated no evidence of increased diarrhea in breastfed infants supplemented with iron-fortified formula
compared with those supplemented with low-iron formula.28 The conclusions of this study were somewhat clouded by the lack of
measurement of the amount of formula supplementation and whether iron
containing beikost or vitamins was consumed. A well-controlled, dose-response study of iron-fortified infant formula supplementation of
breastfed infants with infection and iron endpoints is needed to
resolve this issue. Because no data currently support the use of a
low-iron formula as an alternative supplement for breastfed infants and
low-iron formula is associated with an unacceptably high risk of iron
deficiency, the Committee on Nutrition recommends the use of
iron-fortified cow milk or soy formula as a supplement for breastfed
infants whose mothers choose not to exclusively breastfeed.
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IRON REQUIREMENTS DURING THE FIRST YEAR: INTAKE, ABSORPTION, AND
LOSSES
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THE RATIONALE FOR IRON-FORTIFIED INFANT FORMULAS
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IRON CONCENTRATIONS IN LOW-IRON VERSUS IRON-FORTIFIED COW
MILK FORMULAS
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CAUSES OF RESISTANCE TO THE USE OF IRON-FORTIFIED FORMULAS
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IRON FORTIFICATION AND GASTROINTESTINAL DISTRESS
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CONTINUED MANUFACTURE OF LOW-IRON FORMULAS
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HUMAN MILK IS LOW IN IRON
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LABELING REQUIREMENTS
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POTENTIAL CONTRAINDICATIONS TO IRON-FORTIFIED FORMULAS
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CONCLUSIONS
Top
Abstract
Conclusion
Recommendation
References
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RECOMMENDATIONS |
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COMMITTEE ON NUTRITION, 1997-1998
Susan S. Baker, MD, PhD, Chairperson
William J. Cochran, MD
Carlos A. Flores, MD
Michael K. Georgieff, MD
Marc S. Jacobson, MD
Tom Jaksic, MD, PhD
Nancy F. Krebs, MD
LIAISON REPRESENTATIVES
Donna Blum, MS, RD
US Department of Agriculture
Suzanne S. Harris, PhD
International Life Sciences Institute
Van S. Hubbard, MD, PhD
National Institute of Diabetes and Digestive and Kidney Diseases
Ephraim Levin, MD
National Institute of Child Health and Human Development
Ann Prendergast, RD, MPH
Maternal and Child Health Bureau
Alice E. Smith, MS, RD
American Dietetic Association
Elizabeth Yetley, PhD
Food and Drug Administration
Stanley Zlotkin, MD
Canadian Paediatric Society
SECTION LIAISON
Ronald M. Lauer, MD
Section on Cardiology
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FOOTNOTES |
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The recommendations in this statement do not indicate an exclusive course of treatment or serve as a standard of medical care. Variations, taking into account individual circumstances, may be appropriate.
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ABBREVIATIONS |
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FDA, Food and Drug Administration.
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REFERENCES |
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