Does Breastfeeding Increase IQ?

Summary

More or Less (BBC Radio 4)

Episode: Does Breastfeeding Increase IQ?

Date: March 21, 2015
Hosts: Ruth Alexander & Hannah Moore

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Overview

This episode of More or Less explores the claim that breastfeeding increases a child's intelligence, as popularized by a major Brazilian study receiving widespread media attention. The hosts, with the help of intelligence researcher Dr. Stuart Ritchie, dissect the research, digging into its methodology, statistical robustness, and broader implications about causation versus correlation. The program then shifts to address media exaggerations around a separate study on the safety of vigorous jogging, revealing the often problematic translation of scientific findings into headlines.

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Key Discussion Points

1. The Brazilian Study on Breastfeeding and IQ

[01:04-04:51]

• Study Overview:

  • Researchers in Brazil tracked over 3,000 babies of all social classes from birth into their 30s.
  • Claims made: Babies breastfed for longer scored higher on adult IQ tests and had better life outcomes.

• Historical Context:

  • The link between breastfeeding and intelligence has been studied since the 1920s.

• Study Methodology:

  • Parental education and family income were recorded, but parental intelligence was not directly measured with an IQ test—education years were used as a proxy.
  • In Brazil, breastfeeding is common across all social classes, a notable difference from higher-income countries like the UK.

• Key critique from Dr. Stuart Ritchie (University of Edinburgh):

  • Dr. Ritchie points out the failure to control for parental intelligence as a major flaw.
    • Quote [02:04]:
      “I think there's a major problem with any study of breastfeeding and intelligence that doesn't measure the intelligence of the parents of the child. ... It's actually not that the books or in this case the breastfeeding, is causing higher intelligence, it's just correlated with it.”
  • Ritchie references a systematic review indicating that when parental intelligence or social class is properly controlled for, the apparent effect of breastfeeding on intelligence disappears.
    • Quote [04:09]:
      “Breastfeeding doesn't relate to intelligence.”

• Alternative Study Designs:

  • Studies using sibling or twin comparisons, or direct measurement of parental IQ, show no strong effect.

• Broader Implications:

  • Ritchie cautions: This isn’t a reason against breastfeeding, which has other health benefits; just that boosting IQ may not be one of them.
    • Quote [04:51]:
      “If you're just breastfeeding to give your child a higher intelligence test score, then you might want to rethink that.”

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2. What Actually Influences Children's Intelligence?

[05:10]

• Ruth Alexander summarizes:
  • Two factors proven to influence a child’s intelligence:
    • “Firstly, find someone brainy to have a child with. And secondly, education really can make your child cleverer.” [05:10]

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3. Media Exaggerations: The Jogging Study Example

[05:49-08:53]

• Revisiting headlines from earlier in the year: "Too much jogging as bad as no exercise at all."

• A Danish study followed 1,000 joggers and nearly 4,000 non-joggers for 12 years; found light/moderate joggers lived longer, while “strenuous joggers” did not get the same benefit.

• Flaw in the Study:

  • Only 36 strenuous joggers included; of them, just 2 died during the study period.
    • Quote:
      “How many people in the strenuous jogger category actually died?” – “Two.” [06:34]

• Dr. Alicia White (NHS): Numbers are too small for statistical confidence; causes of death are unknown.

• Exclusive remarks from the study's lead author, Dr. Peter Schnorr:

  • He admits the data is too thin to support the strong conclusion that strenuous jogging is hazardous:
    • Quote [07:23]:
      “You're completely right. We should have said we suspect that it is so, but we can't say for sure. Everybody makes some mistakes in papers.”
    • Quote [07:52]:
      “If you go into the statistics there, you will see confidence limits that are really bad... this is not good statistically, this is too thin.”

• Media Responsibility:

  • Schnorr acknowledges experienced readers could spot the weak statistics, but most journalists don't analyze statistical tables—media amplified the tentative finding.

• Schnorr’s closing guidance: While not proven, he suspects strenuous jogging might not be best for everyone, and regular heart checks may be prudent for marathoners.

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Notable Quotes & Memorable Moments

• Dr. Stuart Ritchie on ignoring key confounders:

  • “It's a bit like saying parents who have more books in their house tend to have more intelligent children and it's the books that cause that...” [02:04]

• Ruth Alexander's tongue-in-cheek advice:

  • “If you want an intelligent child... find someone brainy to have a child with.” [05:10]

• Dr. Peter Schnorr’s rare scientific admission:

  • “Everybody makes some mistakes in papers.” [07:23]

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Timestamps for Key Segments

• [01:04] Media claims about breastfeeding and intelligence
• [02:04] Dr. Ritchie explains the problem with the study
• [03:20] Differences between Brazilian and UK social patterns in breastfeeding
• [04:09] Ritchie on the real relationship between breastfeeding and intelligence
• [04:51] Ritchie clarifies broader health benefits of breastfeeding
• [05:10] Ruth Alexander summarizes what actually affects intelligence
• [06:34] Revealed: only two strenuous joggers died in the Danish study
• [07:23] Dr. Schnorr admits evidence is insufficient for strong conclusions

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Summary

This episode of More or Less unpacks the seductive but misleading narrative that breastfeeding boosts IQ. Despite a widely-cited Brazilian study, intelligence researcher Dr. Stuart Ritchie underscores how failing to rigorously account for parental IQ leaves the core finding unsupported—a classic confusion of correlation with causation. The hosts humorously wrap up with hard evidence: genetics and education shape intelligence far more reliably. The episode exemplifies critical statistical scrutiny, later mirrored in their coverage of hype around health risks of jogging, showing how weak evidence can spiral into assertive, misleading headlines.

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For questions or thoughts, listeners are invited to email [e-mail].

Transcript

[Ruth Alexander]

This is the short edition of More or Less, first broadcast on the BBC World Service.

[BBC Announcer]

Thank you for downloading from the BBC. For details of our complete range of podcasts and our terms of use, go to bbcworldservice.com podcasts.

[Ruth Alexander]

Hello and welcome to More or Less on the BBC World Service. I'm Ruth Alexander.

[Hannah Moore]

And I'm Hannah Moore. This week, the author of a study which claimed to show that stre continuous jogging was bad for you tells us the findings were exaggerated.

[Ruth Alexander]

But first, you'll know, if you're a regular listener, that intelligence is something we prize here at More or Less. We're always thinking of really important things

[Hannah Moore]

like how long is the Runway in Fast and Furious?

[Ruth Alexander]

Six. Yes.

[Hannah Moore]

And where's the most murderous location in a TV detective drama?

[Ruth Alexander]

Well.

[Hannah Moore]

And do cruise holidays encourage infidelity?

[Ruth Alexander]

Yes, there was that one. But anyway, we really were interested when we heard these claims about intelligence.

[Hannah Moore]

Breastfeeding linked to higher iq. The longer babies are breastfed, the more they achieve in life.

[Ruth Alexander]

The results of a major study into breastfeeding has been released to much media attention. The research carried out in Brazil claims to show that babies who are breastfed become more intelligent adults than those given formula. The researchers traced more than 3,000 babies of all social classes over a period of 30 years. Then they gave them an IQ test. Those who were breastfed scored better on average than those who weren't.

[Hannah Moore]

Now, this isn't the first time we've come across a study like this. In fact, scientists have been looking into the link between breastfeeding and intelligence since the 1920s. So we asked a listener about the research.

[Ruth Alexander]

What we just asked a listener, not

[Hannah Moore]

any listener, but a self described loyal listener. Dr. Stuart Ritchie is from the University of Edinburgh in the uk. He researches what influences our intelligence and I asked him what he thought of the study.

[Dr. Stuart Ritchie]

I think there's a major problem with any study of breastfeeding and intelligence that doesn't measure the intelligence of the parents of the child. The reason for that is that it's a major confounding factor. It's a bit like saying parents who have more books in their house tend to have more intelligent children and it's the books that cause that. Well, it might just be that more intelligent parents tend to have more books in their house and they pass on their genes which give them higher intelligence to their children. So it's actually not that the books or in this case the breastfeeding, is causing higher intelligence, it's just correlated with it.

[Hannah Moore]

Now, the Brazilian researchers aren't stupid. They know that intelligent parents tend to have intelligent children, but the question is, did they take the impact of parental intelligence into account?

[Ruth Alexander]

So let's look at the details then. In 1982, the team of researchers visited five maternity hospitals in the southern Brazilian city Pilotus and interviewed almost 6,000 new mums. They asked questions about how long they spent in education, what their family income was, their age, as well as taking details about the pregnancy.

[Hannah Moore]

Two years later, they returned with follow up questions, this time about the father's education and genomic ancestry. They also recorded whether the baby had been breastfed and if so, to what age.

[Ruth Alexander]

One of the interesting things they found was that women from across the social classes were breastfeeding their babies, unlike richer countries like the uk, where breastfeeding is more common among middle and higher earners.

[Hannah Moore]

So it's pretty representative in terms of the family background. But could the researchers find a clear link between being breastfed and what those babies went on to achieve later in life? Between 2012 and 2013, they tried to trace those babies who by then were 30 year old adults. They found most of them more than 3,000 in fact, and recorded information about their education and salary and gave them IQ tests.

[Ruth Alexander]

So they used IQ tests to measure the offspring's intelligence, but they didn't test the parents iq. Instead they relied on the number of years in education as a measure of intelligence.

[Hannah Moore]

According to Dr. Ritchie, that's not good enough.

[Dr. Stuart Ritchie]

So they've tried to control for maternal intelligence by just looking at how many years they stayed in school. But that's not the same thing as actually giving the parents an intelligence test. A review study that came out a couple years ago that systematically reviewed all the studies right across the world that have ever been done on breastfeeding and intelligence concluded that the relationship is proper, probably due to confounding by either social class or the cognitive abilities of the parents. Breastfeeding doesn't relate to intelligence.

[Hannah Moore]

Stuart Ritchie says previous studies show if you control by testing parental IQ or use siblings or twins, the strong relationship suggested by the Brazilian study disappears. Breastfeeding doesn't seem to make your child cleverer.

[Dr. Stuart Ritchie]

I should say that this doesn't mean that you shouldn't breastfeed or that we should stop recommending mothers to breastfeed their kids. Breastfeeding has lots of other clearer benefits, child development and the immune system and so on. These are areas that I'm not expert in. But if you're just breastfeeding to give your child a higher intelligence test score, then you might Want to rethink that.

[Ruth Alexander]

And the research shows, if you want an intelligent child, two things work. Firstly, find someone brainy to have a child with. And secondly, education really can make your child cleverer. You're listening to More or Less. Our email address is more or lessbc.co.uk. Earlier this year, a shock study was published which made headlines around the world. Too much jogging, as bad as no exercise at all. Striking fear into the hearts of hardcore runners.

[Hannah Moore]

The study was a big one. A thousand healthy joggers and almost 4,000 healthy non joggers were studied over 12 years in Denmark. The results were published in the prestigious Journal of the American College of Cardiology and the headline conclusion was that light and moderate joggers live longer on average than people who have sedentary lifestyles. Whereas, and this was the surprise, strenuous joggers don't.

[Ruth Alexander]

Strenuous joggers were, broadly speaking, people who ran for four hours a week at a pace of seven miles an hour.

[Hannah Moore]

At the time, Tim Harford spoke to Dr. Alicia White, who analysed the study for the UK's National Health Service website.

[Dr. Peter Schnorr]

How many people in the strenuous jogger category actually died?

[Hannah Moore]

Two.

[Ruth Alexander]

Two?

[Hannah Moore]

Yes, two.

[Dr. Stuart Ritchie]

That doesn't sound like a lot.

[Hannah Moore]

No, it's not. And only 36 strenuous joggers were studied. So although the overall study was big, the number of strenuous joggers was just too small to draw conclusions. Alicia said. And the researchers don't know what those two people had died from a heart attack, cancer or being knocked down by a bus.

[Ruth Alexander]

We tried to speak to the author of the study, Peter Schnorr, a clinical cardiologist and the founder of the Copenhagen Heart Study, which this research came out of. But he was away. However, we don't give up easily on more or less. We waited until he was back and we've managed to have a word. And you know what? He agrees. He concedes that they didn't have the evidence to say that strenuous jogging is bad for you.

[Dr. Peter Schnorr]

You're completely right. We should have said we suspect that it is so, but we can't say for sure. Everybody makes some mistakes in papers.

[Ruth Alexander]

A complete admission that the evidence wasn't strong enough to support the paper's conclusions. And Peter Schnorr says experienced readers of research papers would have realised that. He says it was obvious from the statistical analysis that you couldn't have confidence in the findings that strenuous joggers had the same average life expectancy as those with a sedentary lifestyle.

[Dr. Peter Schnorr]

It shouldn't have been misunderstood because if you go into the statistics there, you will see confidence limits that are really bad. And if you normally read papers, you could say, ah, this is not good statistically, this is too thin.

[Hannah Moore]

But most journalists around the world weren't going to be delving into the statistical tables. They took their lead from the researchers. Conclusions.

[Ruth Alexander]

So does Peter Schnorr regret all those shock, horror headlines that resulted? Does he worry they might have put people off jogging?

[Dr. Peter Schnorr]

I don't think so, because when you have these deaths, you always have deaths in marathon and so on. If these people had been investigated because they're always a little ischemic heart disease and so on, it could have been prevented. And we're not saying that you should not do the marathon, but we say that maybe every other year you should do an investigation, echocardiography and so on, to look at your heart.

[Hannah Moore]

Peter Schnorr remains convinced that, although he hasn't proved it this time, strenuous jogging might be bad for you.

[Ruth Alexander]

You've been listening to the BBC World Service Numbers Show, More or less. Our website is BBC.com more or less.

[BBC Announcer]

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