Breastfeeding and IQ

Breastfeeding in children has been shown to be associated with higher IQ later in life1. For example, the PROBIT study showed statistically significant effects in Verbal IQ but non-significant effects in full IQ2. However, Emily Oster in Cribsheet, believes the effect is related to confounding variables (maternal IQ, Social Economic Status, etc.)3. She bases this on studies that compared siblings who were breastfed vs. not breastfed. The effect on IQ disappears between these two populations4. This has been backed up by meta-analyses5. Other meta-analyses show the effect is very slight after accounting for confounding6.


Horta, B. L., Loret de Mola, C. & Victora, C. G. Breastfeeding and intelligence: A systematic review and meta-analysis. Acta paediatrica (oslo, norway: 1992) 104, 14–19 (2015).
Kramer, M. S. Breastfeeding and Child Cognitive Development: New Evidence From a Large Randomized Trial. Archives of general psychiatry 65, 578 (2008).
Oster, E. Cribsheet: A Data-Driven Guide to Better, More Relaxed Parenting, from Birth to Preschool. (Penguin Books, 2020).
Der, G., Batty, G. D. & Deary, I. J. Effect of breast feeding on intelligence in children: Prospective study, sibling pairs analysis, and meta-analysis. Bmj (clinical research ed.) 333, 945 (2006).
Walfisch, A., Sermer, C., Cressman, A. & Koren, G. Breast milk and cognitive development the role of confounders: A systematic review. Bmj open 3, e003259 (2013).

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