A large study carried out by scientists in Canada strongly suggests that breast feeding boosts IQ, by about 6 points.
Michael Kramer and his team at McGill University and the Montreal Children's Hospital enrolled over 17,000 infants in a study designed to overcome one of the main criticisms of previous breast-feeding research, that babies who are breast-fed also tend to be born to parents who are themselves better educated, thus accounting for the apparent increase in intelligence. But in this study, dubbed PROBIT (short for Promotion of Breastfeeding Intervention Trial) and published this month in the Archives of General Psychiatry, a group of clinics were randomly assigned either to adopt a programme supporting and promoting breast feeding, or to continue with existing policies. Infants brought to one of these facilities were followed up for 6.5 years.
Using this approach, there were no significant differences between the educational levels of the mothers visiting either the "control" (non-intervention) clinics, or those promoting breast-feeding.
The impact of the intervention was very marked. About 45% of mothers visiting a centre promoting breast feeding were feeding their babies breast milk between 3 months and 1 year of age, compared with only 6% of mothers attending the "control" clinics. When the children were assessed at the age of 6.5 the breast-fed children scored, on average, 7.5 points higher on verbal tests, 2.9 points higher on non-verbal tests and 5.9 points higher on measures of overall intelligence.
Despite this clear relationship, the reason for the effect is still not altogether clear, say the study authors. "Even though the treatment different appears causal it remains unclear whether the cognitive effects of breast feeding are due to some constituent of breast milk, or are related to the physical and social interactions inherent in breast feeding." There are a number of chemicals and nutrients in breast milk could be responsible, including long chain fatty acids and growth factors such as insulin like growth factor 1 (IGF1), but breast feeding could also lead to better verbal interaction between mother and child, which could improve children's cognitive development.