Impact of breast milk
Although observational findings linking Impact of breast milk to higher scores on cognitive tests may be confounded by factors associated with mothers’ choice to breastfeed, it has been suggested that one or more constituents of breast milk facilitate cognitive development, particularly in preterms. Because cognitive scores are related to head size, we hypothesised that breast milk mediates cognitive effects by affecting brain growth. We used detailed data from a randomized feeding trial to calculate percentage of breast milk (%EBM) in the infant diet of 50 adolescents. MRI scans were obtained (mean age=15y9m), allowing volumes of total brain (TBV), white and grey matter (WMV, GMV) to be calculated. In the total group %EBM correlated significantly with Verbal IQ (VIQ); in boys, with all IQ scores, TBV and WMV. VIQ was, in turn, correlated with WMV and, in boys only, additionally with TBV.
No significant relationships were seen in girls or with grey matter to differ in Impact of breast milk. These data support the hypothesis that breast milk promotes brain development, particularly white matter growth. The selective effect in males accords with animal and human evidence regarding gender effects of early diet. Our data have important neurobiological and public health implications and identify areas for future mechanistic study.
Numerous studies report that breastfeeding is associated with higher scores on tests of neurodevelopment and cognition in later life (1,2), suggesting that breast milk may impact early brain development, with potentially important biological, medical and social implications. These findings are often questioned because other factors associated with mothers’ choice to breast-feed (e.g. higher socioeconomic status and level of education, different child-rearing attitudes) might promote cognitive development. In a study using data from a national database, adjustment for maternal IQ eliminated the breastfeeding effect (3). All these studies, however, are potentially flawed by lack of experimental design.
More recently, a large cluster randomised trial of breastfeeding promotion using an experimental design demonstrated a large effect of breastfeeding on cognition, adding credence to the evidence for beneficial effects seen in past observational studies (4). Anderson and colleagues (5) showed in a meta-analysis that, after appropriate adjustments, breastfeeding was associated with an advantage of around 3 points on tests of cognition in children born at term and around 5 points in those born preterm, both large effects in population terms. The implication is that, over and above social factors, one or more constituents of breast milk benefit neurodevelopment, particularly so in those born preterm, at a more sensitive stage of brain development.
Our current study was prompted by two factors, the now likely causal relationship between breast feeding and cognition and the previous observation that cognitive scores in preterms are related to head circumference and brain size measured by quantitative volumetric analysis of MRI scans (6). With this background, we examined the relationships between breast milk feeding, cognition and brain volume determined from MRI scans. Our specific purpose was to provide evidence for the hypothesis that cognitive benefits of breastfeeding are mediated though an effect on brain growth, ultimately influencing mature brain volume.
To explore hypothesis on Impact of breast milk, we studied members of a cohort of adolescents who had participated in a large randomised trial examining the health and developmental effects of early infant nutrition, conducted between 1982-5 (7). The subjects were born preterm, at a sensitive period for nutritional effects on brain development and cognition (8). In exploratory analyses, those receiving breast milk, after allowing for confounding factors, had an 8.3 point IQ advantage at 7-8 years (9). A subset of this cohort has been followed to 13-19 years of age for MRI scanning and cognitive testing.
Data collected on these subjects whilst in the neonatal unit provided precise information on the volumes of breast milk consumed (by nasogastric tube), giving a rare opportunity to explore the potential dose-response effect of breast milk feeding on brain volumes and cognition at adolescence. It is important to note that all neonatal data were recorded for this study at the time and were not obtained retrospectively from charts. Although some IQ data for the larger group have been reported previously (10,11), neither IQ data for this particular group nor information regarding breast milk in the diet have been published.