Is childhood nutrition related to IQ as an adult?

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Yes, to a small degree. We asked our participants (n = 499) several questions related to their childhood nutrition. Specifically, we asked them when they were children, how often they had enough food, how often they ate fruits and vegetables daily, how often they drank milk daily or consumed an alternative source of calcium and how often they ate fast food. Additionally, we asked them if they were breastfed as babies. We obtained two significant, albeit low correlations: r = 0.16 between having enough food in childhood and IQ and r = 0.11 between being breastfed as a baby and IQ. IQ was not significantly correlated with eating fruits and vegetables daily (r = 0.05), frequency of drinking milk or consuming an alternative source of calcium (r = 0.08) or frequency of eating fast food (r = -0.08). Importantly, these results held even after we statistically accounted for participants’ general childhood wealth to make sure that the correlation between, for example, having enough food and IQ does not exist solely because those that had more food were wealthier. Here are the scatterplots of the two statistically significant correlations.

Note that our study was asking adults to self-report about what happened in childhood. These self-reports may not be that accurate, which might reduce the correlations compared to what they would be if measurements had actually been conducted in childhood.

What do the other studies say?

Previous studies generally found that the relationship between childhood nutrition habits and later life IQ exists, but is not particularly strong. For example, Northstone et al. (2012) found that a poor diet associated with high fat, sugar and processed food content in early childhood may be associated with small reductions in IQ in later childhood. Regarding breastfeeding, one earlier meta-analysis by Der at al. (2006) found that breastfeeding has little or no effect on IQ in children, while a more recent one by Horta et al. (2015) found a small benefit of breastfeeding for children's IQ.

Takeaways

• We found that some aspects of childhood nutrition, specifically self-reports (as an adult) of having enough food in childhood and being breastfed as a baby, had a small positive correlation with later life IQ

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