The most valuable of all capital is that invested in human beings; and of that capital the most precious part is the result of the care and influence of the mother.
Alfred Marshall (1890), Paragraph VI.IV.11.
Past studies have shown that breastfeeding babies have higher IQ's by 7-10 points. A new study is saying that only four weeks of breastfeeding raises the cognitive ability of a baby measurable at 5, 7, 11 and 14 years of age.
The difficulty in doing this type of research is controlling for cause and effect variables, especially what type of mother typically breastfeeds. The typical breastfeeding mother in the developed world is of higher social class, has a higher IQ, higher levels of human capital, etc. It would stand to reason that the babies of these mothers would follow suit. Are breastfed babies brighter because that type of mother naturally raises brighter children or are they brighter because they were breastfed?
According to authors Maria Iacovou and Almudena Sevilla-Sanz " we addressed this question of causality by making use of propensity score matching (PSM).... It involves “twinning” each breastfed baby with one or more babies who were not breastfed, but who in all other observable respects are similar to the breastfed baby. In this way, we effectively simulate an experiment by creating matched “treatment”and “control” samples, composed respectively of women who do and who do not breastfeed, but who are identical in every other observable respect (Rosenbaum and Rubin 1984).
Other important parts of this study are the large sample and length of study: approximately 14,000 babies were studied for 14 years. The scores were consistent across Math, English and Science scores and persisted for at least 14 years.
We want mothers to breastfeed for as long as they can, always keeping in the back of their minds the biological norm for weaning falls between a minimum of two and a half years and a maximum of seven years. But for a woman who wouldn't otherwise breastfeed at all, I'd encourage her to set her goal for four weeks. And as I always say:
Give as much breastmilk as you can to your child for as long as you can.
There's no such thing as too little breastmilk when it comes to benefits, though as in many things in life, the more the better.