The effects of diet during the first six months of life on health outcomes in infancy and early childhood

Background: The immediate and long-term benefits of breastfeeding for both mother and infant are well documented, but less is known about the impact of exclusive breastfeeding on health outcomes in infancy and childhood. In 2001 the World Health Organization (WHO) changed the recommended duration of exclusive breastfeeding from the first 4-6 months to the first 6 months of life. The principle reason for this change was to provide optimal nutrition to young infants in low resource countries where available water and complementary foods may be nutritionally inadequate or contaminated. In resource rich countries, the evidence for recommending 6 months of exclusive breastfeeding is less clear, nor are the nutritional consequences to the infant of this recommendation well-tested. Furthermore, recognizing that few randomized controlled trials contribute to the evidence base of the recommendations, the WHO requested such trials to guide future policy decisions in this regard. The principle aim of the present thesis was to enhance our understanding of the effects of diet during the first 6 months of life on health outcomes in infancy and early childhood. Impact of lactation consultants vs. traditional consult in the well-baby clinics on the diet given to infants during the initial complementary feeding period as well as the impact of exclusive breastfeeding for 6 months on total breastfeeding duration were also studied. Methods: 119 mother-infant pairs from 7 healthcare centers in Iceland were randomly assigned to receive complementary foods from the age of 4 months in addition to breast milk (CF), or to continue exclusive breastfeeding to the age of 6 months (EBF). Inclusion criteria in the study for infants were: singleton birth, gestational length ≥37 weeks, exclusively breastfed at the time of assessment and infant characterized as healthy. Furthermore, mothers had to be willing to be randomized into either intervention group. Baseline information was collected on eligible mother-infant pairs. Data were collected on complementary feeding intake at 5.25 months, breast milk intake from 5.5 to 6 months, iron status and infant body composition at 6 months, anthropometric outcomes from birth to 29-38 months of age, developmental and behavioral outcomes at both 18 and 30-35 months of age and total breastfeeding duration. To be able to test the impact of lactation consultants on the diet given to infant’s data were also taken from an additional cohort of infants born between January and December 2005 and randomly selected by Statistics Iceland for a separate national prospective study conducted in Iceland. Inclusion criteria for participation in the study were singleton birth, gestational length at least 37 weeks and absence of congenital abnormalities or chronic health issues. Infants’ dietary intake data was collected prospectively, monthly from 5-8 months of age by 24-hour food recall. Information on total duration of breastfeeding was also collected. Results: Infants in the EBF group consumed significantly more breast milk at 6 months (901±158 g/d) compared with those in the CF group (818±166 g/d; p=0.012). Adjustment for characteristics that were significantly different at baseline did not change the findings. The average energy intake from complementary foods by infants in the CF group was 265.4±219.0 6 kJ/d (63.4±52.3 kcal/d) or 36.8 kJ/kg body weight (8.8 kcal/kg); only 10% of the average daily energy requirements for infants 6-11 months of age. Infants in the CF group had higher mean serum ferritin levels at 6 months of age (p=0.02) that remained significant when adjusted for baseline differences. No difference was seen between groups in the prevalence of iron deficiency anemia, iron deficiency or iron depletion. Furthermore, no difference was seen between groups in growth between 4 and 6 months or infants’ body composition at 6 months. The follow-up showed that duration of exclusive breastfeeding for 4 vs. 6 months did not affect developmental or behavioral outcomes at 18 months or 30-35 months of age. However, at 30-35 months of age a significantly smaller percentage of parents in group CF (2%) had concerns about their children’s gross motor development compared to those in group EBF (19%; p=0.01), which remained significant when adjusted for differences in prerandomization characteristics (p=0.03). Furthermore, the introduction of complementary foods at 4 months did not affect the prevalence of overweight children at 18 months (p=0.74) or 29-38 months of age (p=0.36). In the analysis conducted with the additional cohort from the national prospective study, having unlimited access to lactation consultants appeared to support a slower introduction of complementary foods during the initial complementary feeding period, measured by the number of daily meals consumed by the infants at 6 months (p=0.001). Furthermore, among all mothers with unlimited access to lactation consultants, those who introduced complementary foods at 6 months had a longer duration of total breastfeeding (1.08±0.15) than those with infants receiving complementary foods from 4 months of age (1.01±0.11, 95% CI -0.001, 0.16) and those whose mothers had only routine care instead of unlimited lactation consultations at the well-baby clinics (0.96±0.13, 95% CI 0.03, 0.22). All infants exclusively breastfed for 6 months had similar duration of total breastfeeding, regardless of exposure to lactation consultants. Conclusion: In a resource rich country, exclusive breastfeeding for 6 months does not compromise body composition or growth in infancy, because of similar energy intakes in both intervention groups. Adding a small amount of complementary foods in addition to breast milk to infants’ diets from 4 months has a small and positive effect on iron status at 6 months. The biological importance of this finding remains to be determined. Breastfeeding support may slow the introduction of complementary foods and exclusive breastfeeding for 6 months may enhance more prolonged breastfeeding. No sustained effect of a longer duration of exclusive breastfeeding was seen on selected measures of developmental and behavioral status at 18 months, although at 30-35 months, a smaller percentage of parents of children introduced to complementary foods at 4 months of age expressed concerns about their gross motor development. Furthermore, no effects of exclusive breastfeeding for 4 or 6 months were seen on the risk of being overweight or obese in early childhood. Our results underline the importance for larger randomized controlled trial on optimal duration of exclusive breastfeeding.