[Linkpost] “Breastfeeding and IQ: Effects shrink as you control for more confounders” by Nina Panickssery

Socioeconomic status, parental education, and parental intelligence have strong effects on child IQ and are themselves correlated with breastfeeding practices. When studies ignore these confounders, they often find significant IQ increases in breastfed groups (5-8 points).

As more confounders are accounted for, the gap typically shrinks to 2-3 points. Some relevant studies:

• Der, Batty & Deary, 2006: 5475 children, controlled for most relevant factors including maternal IQ → + ~0.5 IQ points
• Strøm et al., 2019: 1782 children, controlled for most relevant factors including maternal IQ → + ~3 IQ points
• Pereyra-Elías, Quigley & Carson, 2022: 7855 children, controlled for most relevant factors including maternal IQ → + ~4 IQ points

However, the gold standard are sibling studies, where breastfed and non-breastfed siblings, who share the same parents and home environment, are compared. Here the effect shrinks further, though doesn’t go to zero.

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First published:

August 25th, 2025

Source:

https://www.lesswrong.com/posts/FE5ozGyhN2ykeTwj9/breastfeeding-and-iq-effects-shrink-as-you-control-for-more

Linkpost URL:
https://blog.ninapanickssery.com/p/breastfeeding-and-iq

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Narrated by TYPE III AUDIO.