A prospective study of iron status in exclusively breastfed term infants up to 6 months of age

The World Health Organization (WHO) and American Academy of Pediatrics unequivocally recommend that exclusive breastfeeding is the ideal nutrition for infants and is sufficient to support optimal growth for the first six months of life [1, 2]. However, there is controversy about the adequacy of breast milk in maintaining optimum iron status of exclusively breastfed babies. A WHO committee expressed concern that some exclusively breastfed infants may become iron deficient [1]. Glader recommended that infants exclusively breastfed should receive iron supplementation from four months of age [3]. Calvo et al. evaluated the iron and nutritional status of exclusively breastfed infants for a prolonged period in relation to their growth rate and dietary changes and recommended that breastfed infants should be given supplemental iron from the fourth month of life [4]. Dewey et al. also evaluated the effect of introducing complementary foods before six months of age in exclusively breastfed infants in Honduras [5]. They recommended iron drops for breastfed infants with birth weights between 2500 g and 3000 g. But McMillan et al. reported that term breastfed infants did not need supplemental iron until the birth weight tripled, which occurred at about 12 months of age [6]. Similarly Owen et al. found that infants breastfed until 20 weeks of life, had sufficient iron stores at 6 months of age [7]. Zavaleta et al. reported an interesting observation that maternal anemia did not affect breast milk iron or lactoferrin concentration at birth and during early lactation [8]. The iron status of exclusively breastfed infants up to six months of age, in relation to iron and lactoferrin levels of breast milk, has not been evaluated sufficiently. Thus the question of giving supplemental iron to all breastfed infants remains far from settled.

This prospective hospital based study was, therefore, conducted with the following aims and objectives: (i) To measure iron status [Hemoglobin (Hb), total iron binding capacity (TIBC), percent transferrin saturation (%TS), serum iron (SI), serum ferritin] at birth (cord blood), 14 weeks and 6 months and C-reactive protein (CRP) at 14 weeks and 6 months in exclusively breastfed term appropriate for gestational age (AGA) babies born to non-anemic and anemic mothers; (ii) To estimate total iron and lactoferrin in breast milk on day 1, 14 weeks and 6 months after birth; and (iii) To correlate iron status of the infants with iron and lactoferrin levels in the breast milk of their mothers at 14 weeks and 6 months of age.

In this prospective study, the mean weight, length and head circumference of the babies of non-anemic mothers at birth were 2.84 ± 0.25 kg, 49.5 ± 0.5 cm and 34.7 ± 0.4 cm respectively. The mean weight, length and head circumference of the babies of anemic mothers at birth were 2.82 ± 0.24 kg, 49.5 ± 0.6 cm and 34.5 ± 1.1 cm respectively; the groups were similar (p > 0.05). Likewise, the mean weight (44.41 kg and 45.81 kg) and height (145.4 cm and 146.9 cm) of non-anemic and anemic mothers were also similar. All mothers belonged to lower and middle-income groups and were similar in terms of level of education and other socio-demographic factors.

Domelloff et al. were the first to report the reference values for iron status variables in exclusively breastfed infants [13]. They reported Hb >10.5 g/dl as normal 2 SD cut-off at four and six months of age. The 2 SD cut-offs for serum ferritin were < 20 ng/ml and < 9 ng/ml at these ages respectively. In the present study, none of the babies in either group were found to be iron deficient at 14 weeks and 6 months although at 14 weeks of life eight babies were anemic as per these criteria [13]. Their serum ferritin was >41 ng/ml which signified that iron stores were normal. The Hb of all these babies increased to non-anemic ranges (>10.5 g/dl) with normal age-specific serum ferritin levels at six months. The low Hb level in these babies at 14 weeks was not due to iron deficiency but perhaps was a result of delayed onset of haematopoiesis compared to their peers [3]. Once the trigger to start Hb formation was activated these babies produced enough Hb later on, and were able to overcome their earlier deficiency.

Similarly at six months of age, none of the babies in either group were iron-deficient or anemic with a lone exception. In one baby of anemic mother, who had normal Hb level at 14 weeks, the Hb level fell just below 10.5 g/dl (10.4 g/dl) with age-normal serum ferritin level (11 ng/ml) which indicated that the baby was not iron deficient [13]. Our observations regarding Hb, SI, TIBC, %TS and serum ferritin of babies in both groups, at six months of age, were in concordance with other studies [14–16].

Pisacane et al. studied the iron status of 30 infants who had been breastfed until their first birthday and who had never received cow milk, medical iron or iron-enriched formula and cereals [17]. None of the infants who were exclusively breastfed for seven months or more and 43% of those who were breastfed for a shorter duration, were anemic (Hb < 11 g/dl) at 12 months of age. The duration of exclusive breastfeeding was significantly longer among non-anemic infants (6.5 vs 5.5 months) [17]. Murray et al. studied the effect of iron status of Nigerian mothers on the concentration of iron in breast milk and reported that, infants feeding entirely on breast milk appeared to have normal iron status at six months [14]. Duncan et al. followed 33 exclusively breastfed infants from birth to six months for their iron status [15]. They concluded that infants who were exclusively breastfed for the first six months of life were not at a higher risk for the development of iron deficiency anemia or the depletion of iron stores during that time [15].

In another study by Lonnerdal and Hernall of exclusively breastfed infants and infants fed cow's milk based formula containing either 4 mg iron/l or 7 mg iron/l, there were no significant differences in the haematological indices among the groups at 6 months age and the iron status of the infants was satisfactory [16]. They also found that the concentration of serum transferrin receptors was highest in breastfed infants, and lowest in the infants who received high concentration of iron (7 mg/l) [16]. This finding suggested that breastfed infants were probably on the verge of becoming iron deficient, although their serum ferritin levels and other haematological indices were normal. Interestingly, in the above study, the normal haematological values used for comparison were obtained from a selected group of healthy term infants (> 3 kg birth weight) who were receiving continuous iron supplementation during the first year of life [18, 19], but still breastfed infants were not seen doing badly.

As we have reported previously, breast milk iron and lactoferrin concentration had no relationship with the mother's Hb and iron status [11]. The wide range in the breast milk iron values reported in the literature may be due in part, to differences in sampling procedures as well as stage of lactation. Iron content of human milk is highest in early transitional milk (0.97 mg/ml) but decreases steadily during lactation, reaching a level of approximately 0.35 mg/ml at 1 month of lactation to 0.20 mg/ml at 6 months [11, 20–22]. In the present study from birth to six months, the mean breast milk iron ranged from 0.89 to 0.26 mg/l in the non-anemic (group A) and 0.86 to 0.33 mg/l in the anemic (group B) mothers. Mean breast milk lactoferrin levels in non-anemic mothers (group A) were 12.02 mg/ml, 5.84 mg/ml and 5.85 mg/ml respectively at day 1, 6 weeks and 6 months while in anemic mothers (group B), levels were 12.91 mg/ml, 6.68 mg/ml and 6.37 mg/ml respectively at the same time points. No significant difference was noted in the breast milk iron and lactoferrin between non-anemic and anemic mothers on day 1, 14 weeks and 6 months after delivery.

Houghton et al. studied breast milk lactoferrin levels in relation to maternal nutritional status [23]. Lactoferrin concentration was significantly higher in the first 15 days of lactation (ranging from 2.82 mg/ml to 3.49 mg/ml) than later (ranging from 0.66 mg/ml to 1.42 mg/ml). There are few other studies regarding breast milk lactoferrin concentration mainly during early lactation [8, 24, 25]. Lien et al. estimated lactoferrin in the breast milk of mothers from nine countries by HPLC method and reported that its level ranged from 1.37 to 2.12 g/L (mean 1.83 ± 0.67 g/L) and was significantly lower in Mexican and Australian mothers compared to Canadian, Chinese and British mothers [26]. Thus ethnic and racial factors do appear to affect lactoferrin levels in the breast milk. In the above study, Indian mothers were not included. The lactoferrin levels in our study were higher when compared to the available literature. However, lactoferrin levels in our mothers, both non-anemic and anemic, behaved in a completely different way from that reported by Lien et al. [26]. The lactoferrin levels in our mothers decreased significantly from day 1 to 14 weeks of lactation but remained fairly consistent from 14 weeks to 6 months, unlike Australian mothers, where lactoferrin levels remained fairly constant until 350 days of lactation duration, and in contrast to British mothers in whom lactoferrin declined sharply in the same period. Is the obvious difference in the breast milk lactoferrin values in our study because of the method of estimation of lactoferrin, subject variation (race/ethnicity) or a small sample size (n = 13 in each group)? It is a matter for further research. The study has conclusively showed that there was no correlation between the iron status of exclusively breastfed infants with breast milk iron and lactoferrin until six months of age.

Our findings of breast milk iron levels were in concordance with other studies [8, 20, 21]. Many studies in the past have assessed the iron status of exclusively breastfed infants, but unfortunately, very few have attempted to look at the relationship between breast milk iron and lactoferrin with the iron status of exclusively breastfed infants in first six months of life. It was not surprising that exclusively breastfed infants neither developed iron deficiency nor iron deficiency anemia. The breast milk iron and lactoferrin are efficiently absorbed in the gut and together with body iron stores, the iron supply is sufficient to maintain normal iron metabolism in the first six months of life in term AGA babies. Therefore, there is no need to add iron-rich foods or therapeutic iron to exclusively breastfed term infants until six months of life lest it may harm the baby [27].

We found that: (i) Babies of non-anemic and anemic mothers who were exclusively breastfed until six months age did not develop iron deficiency anemia or iron deficiency; (ii) The iron status of the babies had no relation with the breast milk iron and lactoferrin concentration at any particular time; (iii) The declining haemoglobin and serum ferritin of babies of non-anemic and anemic mothers significantly correlated with the declining breast milk iron and lactoferrin concentration. Given the importance of iron nutrition during the first year of life, it was important to address the issue of iron status of exclusively breastfed babies up to six months age and its relation to the breast milk iron and lactoferrin content.