The Journal of Nutrition
Birth Weight of Korean Infants Is Affected by
the Interaction of Maternal Iron Intake and
Jinhee Hur,4Hyesook Kim,4Eun-Hee Ha,5Hyesook Park,5Mina Ha,6Yangho Kim,7Yun-Chul Hong,8
and Namsoo Chang4*
4Department of Nutritional Science and Food Management, and5Department of Preventive Medicine, College of Medicine, Ewha
Womans University, Seoul, Korea;6Department of Preventive Medicine, Dankook University College of Medicine, Cheonan, Korea;
7Department of Occupational and Environmental Medicine, Ulsan University Hospital, University of Ulsan College of Medicine, Ulsan,
Korea; and8Department of Preventive Medicine, Seoul National University College of Medicine, Seoul, Korea
Excessive iron consumption during pregnancy can lead to increased oxidative stress in the maternal body, which may
result in adverse pregnancy outcomes. Glutathione S-transferases (GSTs) originate from a superfamily of detoxifying
enzymes that play a role in reducing xenobiotic compounds and oxidative stress. The aim of this study was to determine
the relationship among GST gene expression, maternal iron intake during pregnancy, and neonatal birth weight. The study
participantswere 1087Koreangravidas and their newborns recruitedfor the Mothersand Children?s Environmental Health
study between 2006 and 2010. A 24-h dietary recall interview was conducted to estimate iron intake; additional intake
through nutritional supplements was thoroughly investigated. Deletion polymorphisms of GSTM1 and GSTT1 were
genotyped using PCR. Dietary iron consumption during pregnancy was positively associated with birth weight in pregnant
women who were GSTM1-present after adjustment for the following covariates: maternal age, prepregnancy BMI,
mother?s education level, log-transformed urinary cotinine level, infant gender, gestational age at term, log-transformed
energy intake, parity, and the use of folic acid supplements (P < 0.05). There were interactions between the GSTM1
genotype and iron intakes from animal foods (P < 0.05), diet (P < 0.05), and diet with supplements (P < 0.05). No
relationship was found between maternal iron intake and birth weight for the GSTT1 polymorphism. This study
demonstrates that increased iron consumption during pregnancy may improve infant birth weight for mothers who are
GSTM1-present, but it might not be beneficial for mothers with the GSTM1-null genotype.J. Nutr. 143: 67–73, 2013.
The importance of iron consumption during pregnancy has been
underscored, because iron deficiency is the most common
nutritional deficit among pregnant women in both developed
and developing countries (1,2). During pregnancy, the required
amount of iron considerably increases to respond to an
expansion of the plasma volume, an increase in the erythrocyte
mass, and the need to promote the growth and development of
the fetal-placental unit (2). This is fulfilled by routine recom-
mendations to increase iron consumption via supplements
during pregnancy. However, the advantages of increased iron
intake, and in particular that from iron supplements, remain
controversial. Paradoxically, although iron deficiency anemia
can induce oxidative stress (3), an excessive intake of iron can
augment iron stores and iron status (4), eventually leading to the
induction of oxidative stress (2) and hemoconcentration (5) in
the maternal blood. This may negatively influence maternal
health and fetal development, leading to the birth of neonates
thatare smallfor their gestationalage (6), preterm delivery (7,8),
and low birth weight (9,10).
The glutathione S-transferases (GSTs) are a superfamily of
phase II xenobiotic metabolizing enzymes that catalyze the
conjugation reactions of various reactive intermediates with
glutathione (11). The human cytosolic GST superfamily is
subdivided into 8 separate classes: a, k, m, v, p, s, u, and z (12).
GSTM1 and GSTT1 are genes for the isoforms of the m and
u classes of GSTs (13), respectively, which contribute to the
detoxification process by reducing reactive metabolites and
oxidative stress (11). Homozygous deletion polymorphisms of
GSTM1 and GSTT1, denoted as null genotypes, result in loss of
function in the corresponding GSTs (m and u, respectively) (14–
16). Ginsberg et al. (17) reported that homozygous GSTM1
deletion was observed in 53% of Caucasians, 58% of Chinese,
and 21% of African Americans, while homozygous GSTT1
1Supported by the Mothers and Children?s Environmental Health Study of the
National Institute of Environmental Research, Korea.
2Author disclosures: J. Hur, H. Kim, E.-H. Ha, H. Park, M. Ha, Y. Kim, Y.-C. Hong,
and N. Chang, no conflicts of interest.
3Supplemental Figure 1 is available from the ‘‘Online Supporting Material’’link in
the online posting of the article and from the same link in the online table of
contents at http://jn.nutrition.org.
* To whom correspondence should be addressed. E-mail: firstname.lastname@example.org.
ã 2013 American Society for Nutrition.
Manuscript received March 20, 2012. Initial review completed April 18, 2012. Revision accepted October 2, 2012.
First published online November 21, 2012; doi:10.3945/jn.112.161638.
deletion was seen in 20% of Caucasians, 57% of Chinese, and
22% of African Americans. About 53.6 and 53.7% of Koreans
have homozygous gene deletions in GSTM1 and GSTT1,
respectively (18–20). Due to the relatively high polymorphism
frequency of GSTs in human populations (21,22) and their
critical roles in cellular protection against xenobiotic toxicants
and oxidative stress (23,24), 2 major isoforms (GSTM1/GSTT1)
have been extensively investigated and it has been hypothesized
that they are associated with susceptibility to adverse pregnancy
outcomes such as preterm delivery (25,26), younger gestational
age at birth (27), and recurrent pregnancy loss (28).
Several studies have found associations between the GSTM1/
GSTT1 polymorphisms and the effects of maternal exposure to
smoking (29–31), heavy metals (32), or particulate matter (33)
on neonatal birth weight. GSTM1/GSTT1 polymorphisms,
excessive iron intake, and pregnancy itself increase the vulner-
ability to oxidative stress (34,35). However, to the best of our
knowledge, the relationships and associations among GSTM1/
GSTT1 polymorphisms, maternal iron intake, and birth out-
comes remain elusive. Thus, this study was conducted to
investigate the relationships among the presence of GSTM1
and GSTT1, maternal iron intake during pregnancy, and
neonatal birth weight.
Materials and Methods
Study design and participants. This study was conducted as a part of
the Mothers and Children?s Environmental Health (MOCEH) study,
which is a hospital- and community-based, multicenter, prospective,
birth cohort study in South Korea. The details of the MOCEH study are
provided elsewhere (36). The overall procedure of this study was
carefully reviewed and ratified by 3 institutional review boards at the
Ewha Womans University School of Medicine, Dankook University
Hospital, and Ulsan University Hospital. The purposes and process of
this study were explained to potential participants, following which all
of them provided formal consent to participate.
The study population was recruited between August 2006 and
December 2010 and was initially composed of 1788 pregnant women at
12–28 wk of gestation who agreed to participate in the MOCEH study.
Ofthese, 24mothershadtwins,22 womenspontaneously aborted,and9
had fetuses with a congenital anomaly (e.g., ventriculomegaly, Dandy-
Walker syndrome, ambiguous genitalia, or polydactyly) were excluded,
as were 376 who had not yet delivered a neonate, 96 whose gestational
age at term was either too short (i.e., <37 wk) or too long (>42 wk),
and 33 with pregnancy complications (diabetes and/or hypertension).
Among the remaining 1228 pregnant women, 109 did not have
dietary intake data collected, 3 had a total energy consumption <500
kcal/d, and 29 lacked genotype information; these women were also
excluded. Consequently, 1087 participants were finally included in
General characteristics and pregnancy outcomes. The method used
to survey the general characteristics of the participants is described in
detail elsewhere (37). The demographics, socioeconomic status, and
health-related behaviors were gathered by well-trained interviewers.
Biological samples (blood and urine) were collected and dietary
questionnaires were administered on the same day at #20 wk of
gestation. The data collected on pregnancy outcomes from medical
records included neonatal gender, gestational age at term (days), birth
weight (grams), and birth height (centimeters). Gestational age at
delivery was inferred by the last menstrualperiod and was also estimated
Dietary assessment. Maternal dietary intake data during pregnancy
were obtained through a person-to-person interview by a well-trained
dietitian using a 24-h dietary recall method. All of the pregnant women
were asked if their intake on the day of the 24-h recall was representative
of their typical intake. Their nutritional supplements status was
investigated on the same day as the dietary interview. Complete
information about the type, brand name, frequency of use, dose, and
supplement facts of the supplements was gathered. The main iron
supplements consumed by the participants included ferrous fumarate
and ferrous aminoacetosulfate, and the form of the most frequently
consumed folic acid supplements was pteroylglutamic acid. The dietary
intake of nutrients was analyzed further using a program for the
computerized analysis of nutrition (CAN-Pro 3.0). The assessed level of
iron intake represented that from both the diet and supplements. For
further analysis, iron intake was classified into 4 categories according to
the different intake sources: plant foods, animal foods, diet, and diet
GSTM1 and GSTT1 genotyping. Genomic DNA was isolated from
the collected whole blood with the aid of a QIAamp DNA blood kit,
and GSTM1 and GSTT1 genetic polymorphisms were evaluated
using a PCR method. Two primers were used for the amplification
reaction: 5#-GAACTCCCTGAAAAGCTAAAGC-3# (forward) and
5#-GTTGGGCTCAAATATACGGTGG-3# (reverse) for GSTM1, and
5#-TCACCGGATCATGGCCAGCA-3# (forward) and 5#-TTCCTT-
ACTGGTCCTCACATCTC-3# (reverse) for GSTT1. Each 20 mL of
the PCR reaction mixture contained 10 mmol/L Tris-HCl (pH 9.0),
40 mmol/L KCl, 1.5 mmol/L MgCl2, each dNTP at 2.5 mmol/L, 1 unit
of Taq polymerase, forward and reverse primers at 20 pmol/mL, and 50–
100 ng of genomic DNA as a template. Coamplification of a 268-bp
fragment of the b-globin gene, as a positive control, was simultaneously
conducted with the amplification of GSTM1 and GSTT1. The ampli-
fication process was as follows: initialization at 94?C for 5 min; 35 cycles
of denaturation at 94?C for 1 min, annealing at 60?C for 1 min, and
elongation at 72?C for 1 min; and a final elongation at 72?C for 7 min.
Amplification of the PCR reaction mixtures was realized using a PTC-
200 thermal cycler. The GSTM1 and GSTT1 genotypes were determined
based on the presence of a 215-bp product and a 480-bp product,
respectively (Supplemental Fig. 1) (14). DNA fragments were electro-
phoresedthrough a 3%3:1 NuSieve/agarose gel. A homozygous deletion
of the gene was considered null. The genotyping results were checked by
reexamining 10% of the samples arbitrarily selected, which yielded
Statistical analysis. Descriptive analysis was conducted to evaluate the
general characteristics, health-related behaviors, dietary intakes, and
pregnancy outcomes of the study population. Continuous variables (age,
anthropometry, dietary intake, urinary cotinine concentration, and birth
size) are expressed as mean 6 SEM values and categorical variables
(socioeconomic status, neonatal gender, and frequencies of smoker and
supplements user) are expressed as frequencies and percentages. Differ-
ences in characteristics according to genotype groups were tested using
Student?s t test or a chi-squared test. Nutrient intake data and urinary
cotininelevels (thelatter being areliable biomarker of nicotineexposure)
(38) were log-transformed to normalize the statistical distribution. We
conducted multiple regression analysis to investigate the relationships
between neonatal birth weight and maternal iron intake relative to their
GSTM1 and GSTT1 genotypes, and a generalized linear model was
performed to substantiate the gene-nutrient interaction and its effects on
neonatal birth weight. In the latter model, we used median values of
maternal iron intake to assign an equal number of participants to each
group. The following variables were considered as potential confounders
that influence the relationship between maternal iron intake and
neonatal birth weight (according to univariate analysis of the present
data or as reported in the literature) (32,39) and were included in a
multiple regression and a generalized linear model as covariates:
maternal age (y), prepregnancy BMI (kg/m2), mother?s education level
(#high school, #university, and $graduate school), log-transformed
urinary cotinine level (mmol/mol creatinine), infant gender, gestational
age at term (d), the logarithm of the energy intake (kcal), parity, and the
use of folic acid supplements (40,41). Statistical analysis in this research
was conducted using the SAS 9.2 statistical package. All reported
probability tests were 2-sided and the difference was considered
significant at the 5% level.
68Hur et al.
General characteristics. The participants? baseline character-
istics, pregnancy outcomes, and dietary intakes did not differ
between the GSTM1 and GSTT1 genotypes (Table 1). The
prevalence of a homozygous gene deletion in GSTM1 and
GSTT1 was 57.0 and 53.0%, respectively, while that of a
double-null genotype was 31.2%.
Iron intake. The total iron intake of the pregnant women was
35.3 6 1.3 mg/d (12.7 6 0.1 mg/d from diet and 22.6 6 1.3 mg/d
from nutritional supplements) and they consumed 9.6 6 0.1 mg/d
iron from plant food sources and 3.1 6 0.1 mg/d from animal
food sources at midpregnancy (Table 2). Large variations in
total iron intake were attributable to the wide variation in iron
intake from supplements. Iron consumption from plant and
animal food sources significantly differed between groups with
a disparate GSTM1 genotype, but it was difficult to assign any
biological meaning to this finding because the differences between
groups were <1 mg/d.
Maternal iron intake and neonatal birth weight according
to GSTM1/GSTT1 genotype. In this study, neither maternal
iron intake (from all intake sources) nor the GSTM1/GSTT1
polymorphisms significantly affected neonatal birth weight (as
assessed using the F-test; data not shown). However, when the
maternal iron intake and GSTM1/GSTT1 polymorphism vari-
ables were included in the multivariate regression model, dietary
iron intake (P < 0.05) and iron from plant foods (P < 0.05) were
positively associated with infant birth weight for mothers who
were GSTM1-present (Table 3). There was no relationship
between the maternal iron intake and birth weight in carriers
of the GSTT1 polymorphism. For the GSTM1/GSTT1 double-
present genotypes, there was a positive association between the
Characteristics of the pregnant Korean women included in this study1
nAll participantsnPresent (43.0%)nNull (57.0%)nPresent (47.0%)nNull (53.0%)
Prepregnancy weight, kg
Prepregnancy BMI, kg/m2
Education, n (%)
Family monthly income, US$, n (%)
Cigarette smoker, n (%)
Urinary cotinine, mmol/mol creatinine
Serum folate, nmol/L
Neonatal gender, n (%)
Gestational age at delivery, wk
Birth weight, kg
Birth height, cm
Low birth weight (,2500 g), n (%)
Total folate,3mg DFE/d
Dietary folate, mg DFE/d
Supplemental folic acid, mg DFE/d
Iron supplement user, n (%)
Folic acid supplement user, n (%)
30.1 6 0.1
161 6 0.2
56.0 6 0.3
21.6 6 0.1
30.0 6 0.2
161 6 0.2
56.1 6 0.4
21.6 6 0.2
30.1 6 0.1
161 6 0.2
56.0 6 0.4
21.6 6 0.1
30.2 6 0.2
161 6 0.2
55.8 6 0.4
21.5 6 0.1
30.0 6 0.2
161 6 0.2
56.3 6 0.4
21.7 6 0.2
27.3 6 5.8
26.7 6 0.7
17.7 6 4.7
27.9 6 1.1
34.6 6 9.7
26.1 6 0.7
24.0 6 6.5
27.4 6 0.9
30.2 6 9.4
26.3 6 0.9
1087468 619 511576
39.4 6 0.0
3.30 6 0.0
50.7 6 0.1
39.4 6 0.1
3.29 6 0.0
50.6 6 0.1
39.4 6 0.0
3.31 6 0.0
50.8 6 0.1
39.4 6 0.1
3.29 6 0.0
50.8 6 0.1
39.4 6 0.0
3.31 6 0.0
50.7 6 0.1
1.81 6 0.0
276 6 2.4
69.8 6 0.7
48.9 6 0.7
615 6 11.9
352 6 4.1
263 6 11.2
1.80 6 0.0
276 6 3.7
68.5 6 1.1
48.5 6 1.0
618 6 17.8
354 6 6.4
264 6 16.7
1.82 6 0.0
276 6 3.2
70.8 6 1.0
49.2 6 1.0
612 6 16.0
350 6 5.3
262 6 15.1
1.79 6 0.0
275 6 3.4
69.3 6 1.1
47.8 6 1.0
618 6 17.7
348 6 5.9
269 6 16.8
1.82 6 0.0
277 6 3.4
70.2 6 1.0
50.0 6 1.0
612 6 16.1
355 6 5.6
257 6 15.0
1Values are mean 6 SEM unless otherwise stated. DFE, dietary folate equivalents.
2No significant differences were evident between the genotypes.
3Total intakes from diet and supplements; the Estimated Average Requirements and Recommended Nutrient Intake of folate for Korean pregnant women are 520 and 600 mg
Iron, GST polymorphisms, and birth weight69
iron intakes from the total diet (P < 0.05) and from plant foods
(P < 0.05) and neonatal birth weight.
Gene-nutrient interaction and its effects on birth weight.
There were significant gene-nutrient interactions with the
GSTM1 genotype and iron intakes from animal foods, diet,
and diet with supplements (P < 0.05) (Fig. 1). For the GSTM1-
present genotype, birth weight was higher (60.7–79.3 g) in
neonates whose mothers had an iron consumption above the
median value than in neonates of mothers with lower iron
intakes. In contrast, for the GSTM1-null genotype, the birth
weight of neonates whose mothers had iron intakes above the
median value was lower (28.7–65.9 g) than that of neonates
hand, no significant interaction existed for the GSTT1 genotype.
This study investigated the relationships among GSTM1/GSTT1
polymorphisms, maternal iron intake during pregnancy, and
neonatal birth weight. No relationship was found between
neonatal birth weight and either maternal iron intake or
GSTM1/GSTT1 polymorphisms. However, dietary iron con-
sumption was positively associated with infant birth weight for
mothers who were GSTM1-present. There were significant
interactions between the GSTM1 genotype and iron intakes
from animal foods, diet, and diet with supplements.
The mean total iron intake of the participants was between
the recommended nutrient intake (24 mg/d) and the tolerable
upper intake level for iron for pregnant women (45 mg/d)
recommended by the Dietary Reference Intakes for Koreans,
2010 (42). Our participants had a lower dietary iron intake
compared with the iron consumption of other pregnant Korean
women (19.1 6 9.6 mg/d) (43). However, this may be attrib-
utable to the use of different dietary assessment methods (24-h
dietary recall vs. semiquantitative FFQ).
Although increased iron consumption during pregnancy can
be advantageous to neonatal birth weight by preventing anemia-
or iron deficiency-related adverse pregnancy outcomes, exces-
sive iron intake can be a risk factor for undesirable pregnancy
outcomes (2,34). Iron excess may lead to damage related to
increased levels of free radicals (35). As a transition metal,
the reactive form of iron (Fe2+) promotes the production of
hydroxyl radicals from hydrogen peroxide via the Fenton and
Haber-Weiss reactions. If not scavenged, the hydroxyl radicals,
which are very reactive free radicals in vivo, further react with
phospholipids in organelle membranes and produce lipid per-
oxides that can damage cells, tissues, and organs in the body
Pregnancy is a physiological state with increased susceptibil-
ity to oxidative stress and a series of processes, including
Dietary iron intakes of pregnant Korean women by GSTM1 and GSTT1 genotype1
GSTM1 genotypeGSTT1 genotype
Diet + supplements, mg/d
Plant foods, mg/d
Animal foods, mg/d
35.3 6 1.3
12.7 6 0.1
9.6 6 0.1
3.1 6 0.1
22.6 6 1.3
33.8 6 1.9
12.9 6 0.2
9.9 6 0.2*
3.0 6 0.1*
20.9 6 1.9
36.4 6 1.8
12.6 6 0.2
9.3 6 0.1
3.3 6 0.1
23.8 6 1.8
35.6 6 1.9
12.8 6 0.2
9.6 6 0.1
3.2 6 0.1
22.8 6 1.9
35.0 6 1.8
12.7 6 0.2
9.6 6 0.2
3.1 6 0.1
22.3 6 1.8
1Values are mean 6 SEM (all such values). *Different from corresponding null, P , 0.05.
intake from various sources in pregnant Korean women by
GSTM1 and GSTT1 genotype (n = 1087)
Associations between infant birth weight and iron
b (SE)Pb (SE)P
Diet + supplements
Diet + supplements
Diet + supplements
1Iron intake data (mg) were log-transformed.
2Multivariate regression models adjusted for maternal age, prepregnancy BMI,
mother?s education level, urinary cotinine level (log-transformed), infant gender,
gestational age at delivery, energy intake (log-transformed), parity, and the use of folic
acid supplements as covariates; adjustment may have resulted in slight decreases due
to missing values for some variables.
70Hur et al.
implantation, proliferation, differentiation, and trophoblast inva-
sion, generate reactive oxygen species (46,47). Because iron is
abundant in the placenta, which is an oxygen-rich environment
throughout gestation (35), excessive iron consumption during
pregnancy may contribute to increased oxidative stress. Rehema
et al. (48) reported that the concentration of oxidized glutathione
(an oxidative stress marker) was significantly higher in an iron-
supplemented group compared with the control group. Further-
more, recent studies have indicated that oxidative stress is
related to the risk of adverse pregnancy outcomes, such as
being small for gestational age (49,50), intrauterine growth
retardation (51), and low birth weight (52,53).
The GSTM1/GSTT1 polymorphisms can lead to different
expressions of the corresponding enzyme GSTs and diminish the
detoxification process against disease-related xenobiotics (e.g.,
carcinogens) (14), reactive metabolites, and oxidative stress
(11). Several studies (26,54) have found elevated oxidative stress
indices in pregnant Asian women with the GSTM1-null and/or
GSTT1-null genotype. Pregnant women with either or both of
the GSTM1/GSTT1-null genotypes had increased levels of
malondialdehyde and 8-oxo-2#-deoxyguanosine and had de-
creased plasma ferric-reducing ability and glutathione compared
with both of the GSTM1/GSTT1-present genotypes (26). Ele-
malondialdehyde have been reported in pregnant Korean women
with the GSTM1-null genotype (54). The GSTM1-null genotype
has been proposed to increase the risks of preterm delivery (25),
shorter gestationalduration atterm (27), and a history of recurrent
pregnancy loss (28).
We found that there was a positive association between
dietary iron intake (log-transformed) and neonatal birth weight
in pregnant women with the GSTM1-present genotype (n = 468)
alone as well as the GSTM1/GSTT1 double-present genotype
(n = 231). In contrast, in those with the GSTT1 polymorphism
alone, there was no association with maternal iron consumption
and neonatal birth weight. The molecular mechanisms under-
lying this finding remain to be elucidated. It has been indicated
that although the combined null genotypes in these 2 genes are
associated with increased mortality in epithelial ovarian cancer
(55), the enzymatic functions of GSTT1 alone in reproductive
organs remain to be clarified (28). Consistent with our results of
a positive association between dietary iron and birth weight only
in the GSTM1-present genotype, several studies (25,28) have
detected associations between pregnancy outcomes with only
the GSTM1-null genotype, regardless of the GSTT1 status. This
result might also have been due to the numbers of participants
whocarried 1 compared with 2 copies of theactive GST genenot
being known in this study. GSTM1/GSTT1 heterozygotes
exhibit ~50% of the activity of the wild-type homozygotes
(17,56,57). Thus, the lack of a relationship among GSTT1
polymorphism, iron intake, and birth weight may be attributed
to the unknown proportion of women carrying the heterozygous
Iron from plant foods appeared to be a strong predictor
of birth weight in the GSTM1-present and GSTM1/GSTT1
double-present genotypes but not in the GSTT1-present geno-
type. Very little literature provides a scientific explanation for
this particular finding, so future studies are warranted to identify
the mechanisms underlying this.
In the present study, neonatal birth weight was not related
to either maternal iron consumption during pregnancy or the
GSTM1/GSTT1 polymorphisms. However, when the effects
of iron consumption and the GSTM1/GSTT1 polymorphisms
were simultaneously present, there were significant gene-
nutrient interactions between the GSTM1 genotype and iron
intakes from animal foods, diet, and diet with supplements.
Although significant, the magnitude of the birth weight difference
(28.7–79.3 g) may not be biologically relevant, because there
were no differences in gestational age or the incidence of pre-
term birth or low birth weight between groups with disparate
GSTM1 genotypes. However, it is notable that the GSTM1-iron
interaction had some impact on birth weight and the difference
animal foods (B,F), diet (C,G), and diet with supplements (D,H), and GSTM1 (A–D) or GSTT1 (E–H) genotype. Values are adjusted means and SEM
(n = 959) calculated by generalized linear models adjusted for maternal age, prepregnancy BMI, mother?s education level, urinary cotinine level
(log-transformed), infant gender, gestational age at delivery, energy intake (log-transformed), parity, and the use of folic acid supplements as
Estimated birth weights of Korean babies as a function of the interaction between maternal iron intake from plant foods (A,E),
Iron, GST polymorphisms, and birth weight 71
is comparable with that reported by Christian et al. (58), who
observed an increase in birth weight (;60 g) by multiple
micronutrients or folic acid-iron supplementation. We extrap-
olate that iron-induced oxidative stress and an absence of
GSTM1 activity due to polymorphism may result in lower birth
weight due to an interaction. Future studies to identify the
effects of the underlying molecular mechanisms of the GSTM1-
iron interaction on neonatal birth weight are warranted to
substantiate our findings.
One limitation in interpreting the present data is our lack of
maternal iron stores and iron status data. Maternal hematolog-
ical information could allow a more accurate prediction of the
effect of iron consumption on neonatal birth weight (59,60).
Also, maternal iron intake data acquired by a 24-h dietary recall
method may be inadequate for providing a complete explana-
tion of the patient?s usual daily intake due to day-to-day
variations in dietary intake. However, to minimize bias, well-
trained dietitians applied their best efforts to assist participants
in recalling their daily diet. Furthermore, variations in energy
and iron intake between one 24-h dietary recall and the other
obtained within 2–10 d of an original dietary interview were
1.01 and 1.03%, respectively, in the 2009 Korea National
Health and Nutrition Examination Survey (61). Patients with
infections who were not excluded from the participant list could
represent one of the potential confounding variables and due
to many missing values, we were unable to include alcohol
consumption as a covariate. Characterization of other genotype
possibilities that can affect oxidative stress metabolism as well
as enzymatic activity for heterozygotes and assessment of some
specific oxidative markers might also have improved the relia-
bility of our results.
To our knowledge, this is first investigation to demonstrate
that a GSTM1-nutrient interactionaffects neonatal birthweight.
In addition, regarding the distinctive metabolic roles of GSTs
and the high frequency of genetic polymorphisms in the Korean
population, this study involving oxidative stress-susceptible
pregnant women has important implications for public health.
We conclude that increased iron consumption during pregnancy
may improve neonatal birth weights in mothers with the
GSTM1-present genotype but not in those with the GSTM1-
N.C. designed research; J.H., E.-H.H., H.P., M.H., Y.K., and
Y.-C.H. conducted research; J.H. analyzed data; J.H., H.K.,
and N.C. wrote the paper; and N.C. had primary responsibility for
final content. All authors read and approved the final manuscript.
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