Reports of deficient brain development in bottle-fed infants began in the 1970s. A landmark 1978 paper by medical researcher Bryan Rodgers assessed a 1946 birth cohort of children monitored by the National Survey of Health and Development (UK). Rodgers conducted attainment tests with 2,000 cohort children when 8-15 years old. After controlling for family background, children entirely bottle-fed in infancy scored lower than breast-fed children. Differences were small but statistically significant. Many subsequent studies reported similar small differences, with bottle-fed children showing lower average scores on intelligence tests and a higher incidence of learning deficits.
Survey evidence is admittedly circumstantial. Reports that breast-feeding enhances a baby’s mental development are hamstrung by confounding factors. Correlation does not necessarily indicate causation (see my July 12, 2013 post: The Stork-and-Baby Trap). For instance, economic circumstances influence mental development. On average, babies of well-off women perform better on mental tests than babies in lower-income households. But surveys also show that affluent women are more likely to breast-feed. So breast-feeding might be associated with results of mental tests even without a causal link.
However, special statistical techniques are available to control for confounding factors, and careful analyses of survey data eventually left little doubt that mental development is linked to breast-feeding. By 1999, clinical nutritionist James Anderson and colleagues were able to conduct a sophisticated combined analysis of 20 previous studies. To focus on breast-feeding effects, they took particular care to control for confounding factors. The overall outcome was this: Breast-fed babies tested between 6 months and 2 years of age consistently showed significantly higher levels of mental function than bottle-fed babies. Moreover, breast-feeding benefits are even greater for premature babies.
Effect of Breast-feeding Duration
But surveys of breast-feeding benefits generally have an unspoken limitation: Many mothers stop breast-feeding after a few months. Yet comparative evidence from anthropology, archaeology and primatology indicates that our gathering-and-hunting ancestors 10,000 years ago would have breast-fed babies for at least 3 years. So it is biologically appropriate to compare bottle-fed infants with those breast-fed for several years.
In fact, in 1999 Anderson et al. reported another significant finding: Benefits for mental development increased with breast-feeding duration. So nursing for three years rather than just a few months should yield greater benefits. In 1993, developmental biologists Walter Rogan and Beth Gladen threw valuable light on this possibility. In a well-designed prospective study, they tested some 800 children aged between 6 months and 5 years. Their results confirmed the oft-reported finding that average scores are significantly higher in breast-fed than bottle-fed children, albeit by only a few points. More interestingly, however, they showed that scores mounted continuously as breast-feeding duration increased, from a few weeks to over a year.
A prospective study just published by Vasiliki Leventakou and colleagues addressed breast-feeding duration by analyzing data for 540 mother-child pairs from a cohort study in Crete (Greece). Cognitive, language and motor development were assessed with standard tests when children were 18 months old. After controlling for several confounding factors, a positive effect of breast-feeding duration was found for all capacities except gross motor development. For every month of breast-feeding, scores increased by about 0.3 points. So a substantial difference might well result after 3 years, but the study did not distinguish breast-feeding durations beyond 6 months.
Images of Breast-Feeding Benefits
In a novel departure, in 2013 Sean Deoni and colleagues published results of a study using the gentle technique of quiet magnetic resonance imaging (MRI) to examine infant brain development. Deoni et al. examined 133 healthy children aged 10 months through 4 years to estimate white matter, the myelin-sheathed nerve fibres that carry signals in the brain. At any given age, breast-fed children consistently had more white matter in the later-maturing frontal and association regions of the brain. Deoni et al. also found a positive relationship between breast-feeding duration and development of white matter in several brain regions that could account for higher scores in cognitive and behavioral performance measures. Their findings, the authors concluded, “support the hypothesis that breast milk constituents promote healthy neural growth and white matter development”.
Evidence that breast-feeding specifically benefits infant brain development is now convincing, but I want to end with a clear take-home message: For medical and other reasons, many women cannot breast-feed, and they should certainly not be made to feel guilty. My aim is not to advocate a return to our gathering-and-hunting origins but to insist that any substitute for breast-feeding must provide all a baby needs. And we obviously still have much to do, particularly in designing milk formula. Women and babies are biologically adapted for at least three years of breast-feeding, so mothers who nurse their babies for just a few months are to some extent in the same boat as mothers who do not nurse at all. The simplest approach is to breast-feed as long as possible, but what all mothers need and deserve is a suitable formula to use whenever bottle-feeding is the only option.
Anderson, J.W., Johnstone, B.M. & Remley, D.T. (1999) Breast-feeding and cognitive development: a meta-analysis Am. J. Clin. Nutr. 70:525-535.
Deoni, S.C.L., Dean, D.C., Piryatinksy, I., O'Muircheartaigh, J., Waskiewicz, N., Lehman, K., Han, M. & Dirks, H. (2013) Breastfeeding and early white matter development: A cross-sectional study. NeuroImage, 82:77-86.
Leventakou,J., Roumeliotaki.T., Koutra,K., Vassilaki,M., Mantzouranis,E., Bitsios,P., Kogevinas,M. & Chatzi,L. (2013) Breastfeeding duration and cognitive, language and motor development at 18 months of age: Rhea mother-child cohort in Crete, Greece. J. Epidemiol. Commun. Health doi:10.1136/jech-2013-202500.
Mortensen, E.L., Michaelson, K.F., Sanders, S.A. & Reinisch, J.M. (2002) The association between duration of breastfeeding and adult intelligence. J. Am. Med. Ass. 287:2365-2371.
Rodgers, B. (1978) Feeding in infancy and later ability and attainment: a longitudinal study. Dev. Med. Child Neurol. 20:421-426
Rogan, J.W. & Gladen, B.C. (1993) Breast feeding and cognitive development. Early Hum. Dev. 31:181-193.