Do short people also have smaller IQs?

Behind the Headlines

Tuesday March 4 2014

The association between height and increased IQ was only slight

Little and large = stupid and smart?

“They’re already called ‘vertically challenged’ – but are short people intellectually challenged too?” is the headline in the Mail Online. The website reports on a gene study which found taller people were more likely to have a genetic makeup associated with increased intelligence.

The study analysed 6,815 unrelated people and found some relationship between height and intelligence, although this relationship was not very strong. They also found evidence that this relationship could be due to shared genetic factors. The researchers hope this and future studies will help them better understand the links between height, IQ, and health.

Perhaps the most important thing to highlight is that the link between height and IQ is not clear cut – so it would be unfair to equate being shorter with being “intellectually challenged”.

 

Punching above their height?

There are many examples from history showing not all short people are “intellectually challenged”.

 

One notable example is the renowned scientist, Sir Isaac Newton. Newton – who famously claimed to be standing on the shoulders of [intellectual] giants – was a modest five feet six inches tall.

Where did the story come from?

The study was carried out by researchers from the University of Edinburgh and other Universities as part of Generation Scotland – a collaboration between the University Medical Schools and National Health Service in Aberdeen, Dundee, Edinburgh and Glasgow. It was funded by the Chief Scientist Office of the Scottish Government Health Directorates and the Scottish Funding Council, the UK Medical Research Council, Alzheimer Scotland and the BBSRC.

The study was published in the peer-reviewed journal Behavior Genetics and has been published on an open access basis so it is free to read online or download.

Unsurprisingly, the UK media’s reporting focuses on the alleged link between height and IQ. Determining whether there was a relationship between height and IQ was not the main aim of the study and the association between these factors was limited.

 

What kind of research was this?

This was a cross-sectional study which looked at whether any relationship between height and general intelligence – in a large sample of unrelated adults – could be explained by shared genetics.

Traits may be correlated because they are controlled by some of the same genes or for other, non-genetic factors, for example if they are developmentally or structurally related.

 

What did the research involve?

The researchers took blood samples from 6,815 unrelated people and extracted DNA from the samples.

Using this DNA they looked at specific single-nucleotide polymorphisms (SNPs) – places where a single letter of the DNA code differs across the population. A change to a single “letter” of DNA can have a significant impact on how an organism develops.

Participants had their general intelligence assessed using four cognitive tests (processing speed, verbal declarative memory, executive function and vocabulary), and had their height measured.

The researchers then looked at whether there was a correlation between height and intelligence. They then used computer analysis to see whether there was evidence that this correlation was due to shared genetics (a genetic correlation).

 

What were the basic results?

After the researchers adjusted for age and sex, they found that height showed some correlation with general intelligence. This meant that there was some tendency for height to increase as intelligence increased – a “phenotypic correlation” (a correlation of observable characteristics). However, this relationship was not particularly strong.

The researchers then looked at the genetics. They found that 58% of the variability in height in people in their sample and 28% of the variation in intelligence were related to the SNPs that they had assessed.

The researchers found a genetic correlation between height and general intelligence. They estimated that 71% of the phenotypic correlation (correlation between observed height and intelligence) was explained by the same genetic variants.

 

How did the researchers interpret the results?

The researchers concluded that they had found a “modest” genetic correlation between height and intelligence, with they said, “the majority of the phenotypic correlation being explained by shared genetic influences.”

 

Conclusion

This study found some relationship between height and intelligence, and found evidence to suggest that this may be due to shared genetic influences on these traits.

Importantly, the association between height and intelligence was relatively small; meaning the link between the two is not clear cut. So it would be unfair to suggest, as some headlines have, that being short equates to being “intellectually challenged”. 

It is also important to note that it’s not clear to what extent the results are due to the way in which traits affect how humans choose a mate, as opposed to the same genes directly affecting height and IQ.

Greater height and IQ have both been linked to better health outcomes, and researchers hope their findings might help them to understand why this is. At the moment, however, the findings do not have any direct implication.

There is not much you can do about how tall you are, aside from buying some killer heels or Cuban boots, but there are plenty of ways you can keep your brain active.

Analysis by Bazian. Edited by NHS Choices. Follow Behind the Headlines on Twitter. Join the Healthy Evidence forum.

Analysis by Bazian

Edited by NHS Choices

Links to the headlines

You’re coming up short in the IQ stakes, titch. The Sunday Times, March 2 2014

They're already called 'vertically challenged' - but are short people intellectually challenged too? Mail Online, March 3 2014

 

Links to the science

Marioni RE, Batty GD, Hayward C, et al. Common Genetic Variants Explain the Majority of the Correlation Between Height and Intelligence: The Generation Scotland Study. Behaviour Genetics. Published online 20 February 2014

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