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Departments of
*
Pediatrics, University of Iowa, Iowa City, IA, and
Preventive Medicine and Community Health, The University of Texas Medical Branch, Galveston, TX
2To whom correspondence should be addressed.
 |
ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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KEY WORDS: • human infants • erythrocyte incorporation of iron • erythrocyte life span • dietary iron
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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), 42 d (Fomon et al. 1988
,
1989
, 1997
) and 56 d (Fomon et al. 1993
) after isotope administration than 14 d after
isotope administration. This increase in circulating isotope from 14 to
56 d after administration agrees with results of Garby et al. (1964)
, who determined the incorporation of
59Fe in circulating erythrocytes of newborn
infants at various times after intravenous injection of
59Fe.
The primary aim of the present study was to determine the quantity of
58Fe present in the circulation for 112 d
after oral administration of the isotope. This information, which is
not available for any age group, including adults, permitted estimation
of the life span of erythrocytes. There is considerable evidence that
the life span of erythrocytes of newborn infants (Pearson 1967
) is appreciably less than the ~120-d life span of
erythrocytes of adults (Bothwell et al. 1979
), and this
is not surprising because erythrocytes of the newborn are known to be
quite different in physical and metabolic characteristics from those of
the adult (Oski 1993
). However, information on the life
span of erythrocytes of infants beyond the newborn period is lacking.
The duration of our study was planned to allow us to determine whether
the life span of erythrocytes of infants beyond the newborn period is
<112 d.
The second aim of this study was to determine whether the level of dietary iron after ingestion of the isotope affects erythrocyte incorporation of an iron isotope. Infants were therefore fed a low-iron formula (LF group)3 or a high-iron formula (HF group) for 28 d after isotope administration. We reasoned that the greater amount of iron absorbed from the HF would offer a greater degree of competition for isotope incorporation than the amount of iron absorbed from the LF. Hence, erythrocyte incorporation of the isotope would be less in the HF than in the LF group. If this proved to be the case, it would have implications for the design of future studies.
Because of the difference in iron stores of younger and older infants, we considered the possibility that results might be age-related and therefore included two age groups: "56-d-old infants" given the isotope at ~56 d of age and "168-d-old infants" given the isotope at ~168 d of age.
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METHODS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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The study protocol was reviewed and approved by the University of Iowa Committee on Research Involving Human Subjects. The study procedures were explained to one or both parents, and written consent was obtained.
The 56-d-old infants (age at time of isotope administration) were enrolled at 42 d of age (Ages given in the text are target ages; actual ages are target ages ± 4 d.) and the 168-d-old infants were enrolled at 154 d of age. From the time of enrollment, both groups were fed the LF. After enrollment (14 d) each infant received two doses of 58Fe (see Administration of 58Fe). Five h after receiving the second dose of isotope, infants assigned at random to the HF group were fed the HF for the remainder of the study, whereas infants assigned to the LF group continued to be fed the LF for 28 d and were then fed the HF for the remainder of the study. Feeding the LF was considered safe for a period of 42 d, but for a longer period would have placed infants at risk of iron deficiency. Erythrocyte incorporation of the isotope was determined 14, 28, 56, 84 and 112 d after administration of the isotope.
Sample size considerations. For the primary aim, the delineation of the pattern of isotope incorporation over time, we estimated that 20 infants per age group would be sufficient for the description of the pattern, should it be consistent, or for the conclusion that the pattern was not consistent. Given the demanding nature of the study protocol, we could expect to enroll 40 infants over 1 y, and we preferred to limit the time of enrollment to 1 y.
In assessing the effect of the level of dietary iron during 28 d
after isotope administration on isotope incorporation, 10 subjects per
age/treatment group would permit detection of a difference of 1.3
SD at 
= 0.05 and with power of 0.8.
Subjects
The subjects were normal infants and, with four exceptions, birth weights were >2,500 g, and gestational ages were 38 to 41.5 wk. Gestational age of subjects 7314 and 7320 was 37 wk. Twins (subjects 7361 and 7362) were born at 36 wk gestation with birth weights of 2,438 and 2,750 g, respectively. With two exceptions (subjects 7301 and 7353), the subjects were Caucasian.
56-d-old infants: Ten infants (four males and six females) were assigned to the HF Group, and 11 infants (five males and six females) to the LF Group.
168-d-old infants: Eleven infants (nine males and two females) were assigned to the HF group, and nine infants (five males and four females) to the LF group.
Feedings
The 56-d-old infants had been breast-fed or fed milk-based or isolated soy protein-based formulas from birth until the time of enrollment. One infant (subject 7309, LF group) continued to be partially breast fed throughout the study but, in addition, was formula fed and at the time of isotope administration was consuming ~300 mL of LF daily. Many of the 168-d-old infants received other infant foods before enrollment. In the "Study Design" we specified the formulas fed before and after 58Fe administration and in "Administration of 58Fe" we described the feedings on the day of isotope administration. The LF formula was Similac (Ross Products Division, Abbott Laboratories, Columbus, OH), which provided ~2 mg of iron (as ferrous sulfate)/L. The HF was Similac with Iron (Ross Products Division, Abbott Laboratories), which provided 12 mg of iron/L.
Other foods. From the time of enrollment until 28 d after isotope administration, except on the day of 58Fe administration, the older infants were permitted to receive certain other foods low in iron, such as fruits and vegetables, but not iron-fortified cereals or meats. Subsequently, infants were permitted to receive any other foods. The younger infants were not permitted to consume other foods until after age 140 d.
In formula-fed infants, other foods generally substitute on an equal energy basis for infant formula. The permitted foods provided on average three times more iron per unit of energy [0.92 mg/100 kcal (418.4 kJ)] than did the LF. However, because other foods generally provided only 10–15% of energy intake, the effect of other foods on total iron intake was small.
Administration of 58Fe
After enrollment (14 d), each infant was admitted to the Lora N. Thomas Pediatric Metabolism Ward. Three h after a morning feeding, a dose of 58Fe was given; 1 h later, a feeding of LF was given, and 3 h after this feeding a second dose of 58Fe was given. One h after the second dose another feeding of LF was given, and the infant was discharged from the ward and, depending on the feeding group to which an infant was assigned, received the HF (HF group) or continued to receive the LF (LF group).
The 58Fe was prepared in the form of ferrous
sulfate as previously described (Janghorbani et al. 1986
), and each dose of 0.4 mg of 58Fe in
0.45 mg of total iron was administered with 5 mL of a 5 g/L glucose
solution containing 10 mg of ascorbic acid. The isotope was delivered
by syringe directly into the back of the oral cavity to decrease the
likelihood of regurgitation.
Laboratory analyses
Using a disposable spring-loaded device (Tenderfoot;
International Technidyne Corp., Edison, NJ), blood samples were
obtained before administration of the first dose of
58Fe (baseline) and 14, 28, 56, 84 and 112 d
after its administration. Blood was analyzed for hemoglobin
concentration by Coulter Counter model M430 (Coulter Electronics,
Hialeah, FL), and plasma was analyzed for ferritin concentration by an
immunoradiometric assay using the Quantimune kit (catalog number 190-2001; Bio-Rad Laboratories,Hercules,CA). The
58Fe/57Fe isotope ratio
(IR58Fe/57Fe) was
determined in packed erythrocytes as previously described (Fomon et al. 1995
), using a PlasmaQuad 3 inductively coupled plasma
mass spectrometer (VG Elemental, Franklin, MA). The precision of
measurements at natural abundance (baseline) was between 0.15 and 0.4
(mean 0.24) % relative SD.
Calculation of erythrocyte incorporation of 58Fe
The quantity of administered 58Fe
incorporated into erythrocytes
(58Fe*inc) at a
specified time t after administration of the dose was
calculated as follows:
 |
where 58Fe*inc is expressed in mg, IRt is the determined IR58Fe/57Fe at time t after dosing, IR0 is the determined baseline ratio, Fecirc is the quantity of total circulating iron (mg) at time t; 0.2819 is the natural abundance (atom %) of 58Fe; 57.933 is the atomic weight of 58Fe, and 55.845 is the atomic weight of Fe.
The quantity of total circulating iron (mg) was estimated as follows:
 |
where BV is blood volume in liters (assumed to be 0.065 L/kg body weight), Hb is hemoglobin concentration in g/L and 3.47 is the concentration of iron in hemoglobin (mg/g). In the remainder of this communication, the term "58Fe" will refer to the administered isotope.
Statistical analysis
Values for erythrocyte incorporation of
58Fe (% of dose) and values for plasma ferritin
concentration were transformed to natural logarithms before statistical
analysis to compensate for possible non-normal distributions
(Cook et al. 1969
). Thus, geometric means are presented
throughout this paper, and statistical comparisons pertain to
logarithmic means. Because erythrocyte incorporation increased between
14 and 28 d post-dose and decreased after 84 d
post-dose, a "plateau" value (average of 28, 56 and 84 d
post-dose) was calculated for each subject, and comparisons between HF
and LF groups as well as between the two age groups were made on the
basis of plateau incorporation. Descriptive, associate and ANOVA (both
repeated measures and two-factor univariate) statistics were
performed with SAS (version 6.12; SAS Institute, Cary, NC) using
regression and general linear models procedures. ANOVA results
presented are from two-factor (age group and diet level) analysis
with least significant differences post-hoc tests. Appropriate
linear contrasts of repeated measures over time (within subject) were
generated ANOVA (i.e., 14 d value or 112 d value vs. 28, 56
and 84 d values). The mean of the values for plasma ferritin
concentration at the time of isotope administration and 14 d later
was used for assessment of the relation between plasma ferritin
concentration and isotope incorporation. Significance was at the
= 0.05 error rate, and all tests are stated at the per comparison
error rate.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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) declined over time in the 56-d-old infants but not in the 168-d-old
infants. Ferritin concentrations at the time of isotope administration
(mean of 0 and 14 d after dosing) were significantly higher in the
56-d-old infants (P < 0.001), reflecting the greater
iron stores of the 56-d-old than of the 168-d-old infants at the time
of dosing. Among the 168-d-old infants, the mean plasma ferritin
concentration at the time of isotope administration and 14 d later
tended to be greater for the HF group than for the LF group
(P = 0.17). Log plasma ferritin concentration and log
plateau incorporation were inversely correlated in the 56-d-old LF
group (r = -0.60, P = 0.05) but not in
the 56-d-old HF group nor for the 168-d-old groups.
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56-d-old infants: In both the HF and the LF groups, erythrocyte
incorporation of 58Fe increased beyond 14 d
after isotope administration but remained at a plateau between 28 and
84 d (Table 1
, Fig. 1
). The increase between 14 d and plateau (28 through 84 d
post-dose) was significant both in the HF group (P = 0.018) and in the LF group (P = 0.002). After 84 d
post-dose, there was a decided decline in circulating isotope,
which was significant both in the HF group (P = <0.001) and the LF group (<0.002). We have no explanation for the
greater erythrocyte incorporation of 58Fe by
Subject 7323 at 14 d than at 28, 56 or 84 d post-dose
(Table 1)
.
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, the pattern of erythrocyte incorporation of 58Fe
was generally similar to that in the 56-d-old infants. The difference
between the 14-d value and the plateau value was significant in the HF
group (P < 0.001) but borderline in the LF group
(P = 0.064). The mean 112-d value was significantly
less than the plateau value in both the HF group (P < 0.004) and in the LF group (P < 0.003).
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In the 56-d-old infants, the difference in plateau incorporation of 9.2% of intake in the HF group and 15.4% of intake in the LF group was significant (P = 0.05). In the 168-d-old infants, there was no difference between groups. Overall, the effect of the level of iron intake on plateau incorporation was significant (P = 0.041).
Effect of age
In the HF groups, plateau incorporation values were significantly (P = 0.048) lower in the 56-d-old infants (9.2%) than in the 168-d-old infants (15.5%). In the LF groups, plateau incorporation values were not lower in the 56-d-old infants (15.4%) than in the 168-d-old infants (19.7%). Overall, age had a significant (P = 0.041) effect on isotope incorporation. The interaction term between age and iron level was not significant.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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, 1993
)
but was larger than when the isotope was given with food (Fomon et al. 1989
, 1997
) or with supplemental iron
(Fomon et al. 1995
). In both age groups, the quantity of
58Fe present in circulating erythrocytes
increased from 14 to 28 d after isotope administration, remained
at a nearly constant level from 28 to 84 d and declined between 84
and 112 d after administration. Although blood volume as a percentage of body weight enters into our calculation of the quantity of isotope in circulating erythrocytes and blood volume as a percentage of body weight is known to decrease with advancing age, the decrease is so slight over an interval of 14 or 28 d that our use of a constant value cannot explain the observed increase in circulating 58Fe from 14 to 28 d after isotope administration.
That the quantity of isotope circulating in erythrocytes remained
constant from 28 to 84 d after isotope administration and then
decreased by 112 d was unexpected in view of the results of Garby et al. (1964)
. These investigators administered
59Fe intravenously to five infants, age 5 to
25 d, and found that the quantity of circulating isotope increased
progressively during the 60 d of study for all five infants and
during 90 d for the four infants who remained under observation
for 90 d. We had considered the possibility that there would be a
difference in the initial distribution to temporary iron storage sites
of intravenously administered iron and iron absorbed from an oral dose
and that this difference in initial distribution might affect the rate
at which the administered isotope reached the circulation. However, we
had anticipated that if intravenously administered isotope continued to
increase in the circulation for 90 d that isotope absorbed from an
oral dose would increase after 28 d. We have no basis for
determining whether the difference between our findings and those of
Garby et al. (1964)
relates to the different route of administration of
the isotope, to the age of the infants or to other factors.
Because the quantity of 58Fe in the circulation
was less at 112 d than at 28, 56 or 84 d and because of the
evidence that some of the absorbed 58Fe entered
the circulation > 14 d after 58Fe
administration, the study indicates that the life span of erythrocytes
during infancy is <112 d, perhaps about 98 d. With the exception
of a small and probably nonsignificant difference in the life span of
erythrocytes of 3-mo-old infants (three infants studied) and adults
reported by Vest (1959)
, this is the first evidence that the life span
of erythrocytes of infants beyond the newborn period is less than that
of adults.
The difference observed between the 56-d-old and 168-d-old infants is consistent with our observation (Fomon et al., in press) that utilization of 58Fe (erythrocyte incorporation of absorbed 58Fe) is significantly greater by older than by younger infants. We are not aware of other data in the literature that are directly relevant to the difference in erythrocyte incorporation of iron by older and younger infants and believe that the question should be pursued in further studies. Because plasma ferritin concentrations in our 168-d-old infants were much lower than those in our 56-d-old infants, it is possible that the apparent age-related difference in isotope incorporation is actually an expression of the difference in tissue iron stores.
LF were fed to infants in both age groups until 9 h after the first dose of 58Fe (5 h after the second dose). Thereafter, approximately half of the infants in each group were fed a HF while the remainder continued to be fed a LF. In the 56-d-old infants, erythrocyte incorporation of 58Fe was significantly greater by the LF group than by the HF group. In the 168-d-old infants, the difference in erythrocyte incorporation of 58Fe by the HF and LF groups was in the same direction as in the 56-d-old infants, but the difference was not significant.
The greater erythrocyte incorporation of 58Fe by the LF group than the HF group suggests that one or more steps in iron absorption or in the delivery of absorbed iron to hematopoietic sites differ quantitatively between younger and older infants. Because all infants were fed the same LF for the first 9 h after isotope administration, it seems likely that the HF decreased access of the isotope to hematopoietic sites because of one or more of the following: i) a decrease in the uptake by intestinal mucosal cells of isotope remaining in the intestinal lumen 5 h after its administration, ii) a decrease in the rate of transfer of the isotope from intestinal mucosal cells to circulating transferrin and iii) a decrease in the extent of delivery of the isotope from circulating transferrin to hematopoietic sites. The observation that the difference in erythrocyte incorporation of 58Fe by the HF and LF groups was significant for the 56-d-old infants and not significant for the 168-d-old infants may be related to the greater iron stores of the younger infants. We speculate that because of the difference in iron stores, immediate delivery of absorbed isotope to hematopoietic sites was less by the 56-d-old than by the 168-d-old infants and that there was therefore more 58Fe remaining in transit status in the 56-d-old infants. Any 58Fe that had not yet been transported to hematopoietic sites would be susceptible to competition from dietary iron for incorporation into erythrocytes.
The probability that dietary iron intake after isotope administration affects the erythrocyte incorporation of absorbed iron is relevant to the design of studies in which erythrocyte incorporation of 58Fe is used as an endpoint. By controlling dietary intake of iron during the days between administration of the isotope and the time at which erythrocyte incorporation of the isotope is determined, it may be possible to decrease the variability in erythrocyte incorporation of the isotope within groups and may avoid the likelihood of blunting the difference in erythrocyte incorporation of an iron isotope by iron-sufficient and iron-deficient individuals.
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FOOTNOTES |
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3 Abbreviations used: HF, high iron; LF, low iron.
Manuscript received August 6, 1999. Initial review completed September 17, 1999. Revision accepted November 16, 2000.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMETHODSRESULTSDISCUSSIONREFERENCES |
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1. Bothwell T. H., Charlton R. W., Cook J. D., Finch C. A. Chapter 9. Clinical aspects of ferrokinetic measurements. Iron Metabolism in Man 1979:190-221 Blackwell Scientific Publications Oxford
2.
Cook J. D., Layrisse M., Finch C. A. The measurement of iron absorption. Blood 1969;33:421-429
3. Fomon S. J., Janghorbani M., Ting B.T.G., Ziegler E. E., Rogers R. R., Nelson S. E., Ostedgaard L. S., Edwards B. B. Erythrocyte incorporation of ingested 58-iron by infants. Pediatr. Res. 1988;24:20-24[Medline]
4. Fomon S. J., Ziegler E. E., Nelson S. E. Erythrocyte incorporation of ingested 58Fe by 56-day-old breast-fed and formula-fed infants. Pediatr. Res. 1993;33:573-576[Medline]
5. Fomon S. J., Ziegler E. E., Nelson S. E., Serfass R. E., Frantz J. A. Erythrocyte incorporation of iron by 56-day-old infants fed a 58Fe-labeled supplement. Pediatr. Res. 1995;38:373-378[Medline]
6. Fomon S. J., Ziegler E. E., Rogers R. R., Nelson S. E., Edwards B. B., Guy D. G., Erve J. C., Janghorbani M. Iron absorption from infant foods. Pediatr. Res. 1989;26:250-254[Medline]
7.
Fomon S. J., Ziegler E. E., Serfass R. E., Nelson S. E., Frantz J. A. Erythrocyte incorporation of iron is similar in infants fed formulas fortified with 12 mg/L or 8 mg/L of iron. J. Nutr. 1997;127:83-88
8.
Fomon S. J., Ziegler E. E., Serfass R. E., Nelson S. E., Rogers R. R., Frantz J. A. Less than 80% of absorbed iron is promptly incorporated into erthrocytes of infants. J. Nutr. 2000;130:45-52
9. Garby L., Sjölin S., Vuille J.-C. Studies on erythro-kinetics in infancy. IV. The long-term behaviour of radioiron in circulating foetal and adult haemoglobin, and its faecal excretion. Acta Paediatr. 1964;53:33-41[Medline]
10. Janghorbani N., Ting B. T. G., Fomon S. J. Erythrocyte incorporation of ingested stable isotope of iron (58Fe). Am. J. Hemat. 1986;21:277-288[Medline]
11. Oski F. A. Chapter 2. The erythrocyte and its disorders. Nathan D. G. Oski F. A. eds. Hematology of Infancy and Childhood 4th ed. 1993:18-43 Saunders Philadelphia
12. Pearson H. A. Life-span of the fetal red blood cell. J. Pediatr. 1967;70:166-171[Medline]
13. Vest M. Physiologie und Pathologie des Neugeborenenicterus. Bibliotheca Paediatrica Vol. 69 1959:67 S. Karger Basel-New York
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