Sweden is smarter than France! Or is it?

The debate whether breastfeeding increases children's IQ or not continues. I'm a bit surprised that people interested in this issue rely so much on studies and so little on natural experiments: After all, there are plenty of natural experiments on breastfeeding because different countries cultivate different cultures around breastfeeding. Some health systems started to promote breastfeeding heavily already in the early 1980s. Some don't do it much even today. 

The difference in breastfeeding rates between different countries at different times really is huge. France is the big outlier when it comes to non-breastfeeding. "Approximately 56% of babies in France are breastfed at birth compared with approximately 91% in Germany", this study from 2008 states. That means, 44 percent of babies in France were actually never breastfed, compared to 9% Germany. A list from 2018 shows that France is still an outlier, with breastfeeding rates at 63 percent. 

Here is a very interesting study that compared breastfeeding rates from Sweden, Ireland and the US from 1984 to 2015. The Swedish numbers are especially interesting. And here someone made a graphic with comparisons of breastfeeding rates between a few countries. 

I find the Swedish numbers and the French numbers especially interesting, because French numbers are consistently low and Swedish numbers are consistently high. Already in 1984, 97 percent of Swedish mothers breastfed. Since then, more than 90 percent of mothers have breastfed in Sweden. About half of French mothers seem to have breastfed since the 1980s (this study says 52.5 percent in 1998, for example).

Now to the question: Are Swedish people smarter than French people? I have never heard anyone suggesting that. In virtually every comparison of IQs between nations I have ever seen, France looks like a very normal European country. Plain average. If breastfeeding somehow affected IQ, a non-breastfeeding outlier like France should be an IQ outlier. As far as I know, no one suggests that it is. 

Generation Y is smarter than generation X! Or is it? 

Another possibility is to compare breastfeeding rates over time and the IQ of people of different ages. This study says breastfeeding rates in the US doubled from about 30 percent in 1965 to about 60 percent in the early 1980s. Is there a boost in population level IQ that corresponds to increased breastfeeding rates during a person's year of birth? Again, no one suggests that. To the contrary. The Flynn Effect decreased or was reversed during the same time that breastfeeding rates increased in the whole developed world. 

In Norway, men's IQs increased for every year of birth, up to 1975. Then they started to decline, according to this article. Like in almost every other Western country, breastfeeding rates were rather low in Norway in the 1970s and then increased. 

IQ comparisons are always difficult. Still, if we seriously believe that breastfeeding increases IQ by for example 3 points, we need to believe that French people have lower IQ than Swedes. Alternatively, we need to believe that Swedes and most other Europeans are inherently more stupid than French people, but catch up through breastfeeding. It is the same with people born in the 1970s and the 1980s respectively: Either we need to believe that people born later actually have higher IQs, or we need to believe that they would have had even lower IQs if breastfeeding rates hadn't increased.