he WHO recommends exclusive
breast-feeding (EBF) for the first 6 mo of life to decrease the burden
of infectious disease. However, some are concerned about the effect of
EBF >6 mo on iron status of children in developing countries in which
anemia is prevalent. This study examines the risk of
anemia in relation to the duration of EBF and maternal
anemia
in a birth cohort studied between March 1998 and April 2003. All infant
birth weights were ≥2.2 kg. All mothers received home-based peer
counseling to promote EBF. Infant feeding data were collected weekly.
Nurses measured hemoglobin (Hb) values every 3 mo. Hb was measured in
183 infants at 9 mo of age.
Anemia
at 9 mo was defined as a Hb value <100 g/L. EBF was defined by WHO
criteria and ranged in duration from 0 to 31 wk. At 9 mo, Hb (mean ±
SEM) was 114 ± 0.9 g/L; 23 children (12.5%) had Hb levels <100 g/L.
EBF >6 mo, but not EBF 4-6 mo, was associated with increased risk of
infant
anemia compared with EBF <4 mo (odds ratio = 18.4, 95% CI = 1.9, 174.0). Maternal
anemia was independently (P = 0.03) associated with a 3-fold increased risk of infant
anemia.
These associations were not explained by confounding with other
maternal or infant factors. By linear regression, a lower infant Hb at 9
mo was associated with increased EBF duration among mothers who had a
history of
anemia (β = -0.07, P = 0.003), but not among mothers with no history of
anemia. Infants who are exclusively breast-fed for >6 mo in developing countries may be at increased risk of
anemia, especially among mothers with a poor iron status; greater attention to this issue is warranted. J. Nutr. 136: 452-458, 2006.
KEYWORDS: * infant
anemia * maternal
anemia * exclusive breast-feeding
Iron deficiency is the most common nutrient deficiency and cause of
anemia in childhood (1). Although prevalence rates of
anemia
among healthy term infants 6-18 mo of age are reported to be as low as
2-6% in Western Europe and the United States (2-4), iron deficiency
anemia
was shown to affect more than half of the children in some developing
countries (5). In Mexico, 27% of children <5 y old are anemic (6,7). A
national probabilistic survey of Mexican children reported the
prevalence of
anemia to be 13% at 6-11 mo of age, but as high as 49% among children 12-24 mo old (8). Varying degrees of
anemia in young children are associated with poor cognitive outcomes (9-13).
Anemia
diagnosed at 8 or 9 mo of age has been associated with significantly
lower achievement scores in 2nd grade children (14) and impaired motor
development at 18 mo (15). Iron deficiency
anemia
was also shown to be significantly associated with mental retardation
(16), decreased activity, increased wariness or hesitance, and remaining
in close proximity with caregivers (17).
Although the iron in human milk is highly bioavailable (~50% absorption)
(18-21), the iron content is at its highest in early transitional milk
and decreases steadily over the course of lactation (22). In general,
infants born at term and with an adequate birth weight have sufficient
iron stores for the first 4-6 mo of life. However, evidence suggests
that infants with adequate birth weight born to anemic mothers have low
iron stores and are more likely to develop
anemia
(23-26). By 6 mo, complementary foods are required to provide the iron
and other nutrients necessary for infant development (27,28). A
randomized trial conducted in Honduras concluded that at 6 mo, the risk
of iron deficiency is low among exclusively breast-fed (EBF)4 infants
with birth weights >3000 g (29), although infants who were
exclusively breast-fed to 6 mo had significantly lower hemoglobin (Hb)
levels (104 g/L) than infants who had received iron-fortified
complementary foods (109 g/L). Simple iron-fortified complementary
feedings before age 6 mo, however, were not sufficient to prevent
anemia
among the study infants. A second trial, conducted on micronutrient
deficiencies during the period of EBF among term, low-birth-weight
infants (1500-2500 g) in Honduras, found that infants who received iron
supplements did not benefit from complementary foods at 4-6 mo. Dewey et
al. (30) thus recommended that term, low-birth-weight infants be
exclusively breast-fed for 6 mo with iron supplementation.
In 2001, the WHO issued the recommendation for EBF for the 1st 6 mo of
life (31). EBF reduces infant mortality due to common childhood
illnesses such as diarrhea or pneumonia, and is associated with shorter
recovery time during illness (32). There is some concern, however, about
the potential for increased risk of
anemia associated with longer duration of EBF in populations with a high prevalence of maternal and infant
anemia.
Between 1998 and 2003, we conducted a cohort study of breast-feeding
mother-infant pairs in Mexico City. Following the protocol of our
previous community-based efficacy trial of breast-feeding support (33),
we provided peer breast-feeding counseling to all study mothers in this
cohort with the goal of achieving the WHO recommendations for EBF for 6
mo. This counseling was associated with a median duration of 3-4 mo
exclusive breast-feeding, much longer than previously seen in this
population. To determine the effect of this new pattern, we examined the
association between EBF, maternal
anemia, and other factors in relation to the prevalence of
anemia among infants in our cohort.
SUBJECTS AND METHODS
Population. From March 1998 to April 2003, .306 infants in San Pedro
Martir, Mexico City, were enrolled and monitored prospectively from
birth to 2 y of age as part of an ongoing NIH-funded study of human milk
immune protection against diarrheal diseases. The geographic and
socioeconomic characteristics of this community were described
previously (34,35). All enrolled infants were healthy, full-term infants
born without congenital defects, whose mothers agreed to breast-feed.
Potential subjects were excluded if consent was refused, the mother did
not plan to breast-feed, or the infant was low birth weight, premature,
or had a congenital malformation that might affect their ability to
breast-feed. Mother-infant pairs received 3 home-based peer counseling
visits to support exclusive breast-feeding (33), once in the 3rd
trimester, and twice in the first few weeks postpartum. In addition,
mothers were visited in their homes weekly by a trained study worker to
collect standardized data on infant feedings and occurrence of diarrhea
in the past 24 h. Weight and length of the infants were recorded
monthly. This study was approved by the institutional review boards of
the Institute Nacional de Ciencas Medicas y Nutricion and Cincinnati
Children's Hospital Medical Center. Written informed consent was
obtained from the parents of study children.
