People who are genetically predisposed to have higher levels of Fusicatenibacter bacteria scored better on verbal and mathematical tests, while those with more Oxalobacter scored lower.
The levels of certain bacteria in our guts have been linked to varying degrees of intelligence, as determined by scores on verbal and mathematical tests. But whether people could take supplements that change their gut bacteria and improve these skills is unclear.
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| Bacteria in the intestine, some of which may influence how you score on verbal and mathematical tests NOBEASTSOFIERCE/SCIENCE PHOTO LIBRARY |
Several studies have linked the mix of bacteria in the gut, or the gut microbiome, to memory or the ability to learn. But this could be down to people’s level of education influencing their food choices, which then affects the microbiome.
To understand if some gut bacteria directly influence markers of intelligence or if there is just a correlation between the two, Tie-Lin Yang at Xi’an Jiaotong University in China and his colleagues analysed the potentially causal effects of two groups of gut bacteria, called Fusicatenibacter and Oxalobacter. Known as Mendelian randomisation, this kind of analysis uses the random genetic variation that occurs among people as a stand-in for the levels of the bacteria that may otherwise be assigned in a traditional randomised control trial.
The researchers analysed microbiome and genome data previously collected from more than 18,000 people. They pinpointed 10 genetic variants that have previously been linked to levels of Oxalobacter bacteria in people’s guts and 14 genetic variants linked to Fusicatenibacter. They also analysed the verbal and mathematical test scores, and genome data, of a separate group of over 260,000 people.
When exploring if the gene variants were associated with markers of intelligence, they found that people who are genetically predisposed to have more Oxalobacter species in their gut had lower test scores, while those predisposed to have more Fusicatenibacter scored higher.
But the extent to which these test scores reflect someone’s intelligence is unclear. “Verbal and mathematical tests are a pretty good proxy for intelligence, [but] it’s such a complex and multifactorial trait that can’t be bottled down to one or two measures,” says Kaitlin Wade at the University of Bristol, UK.
To gauge whether bacterial levels influence intelligence scores, rather than simply being correlated with them, the researchers identified more than 150 genetic variants that have been associated with verbal and mathematical skills. They then looked for links between these variants and levels of the two bacteria, which suggested that the bacteria may directly affect intelligence.
In the case of Fusicatenibacter, the researchers also linked higher levels of the bacteria to a larger brain volume, which has been associated with intelligence. But how Oxalobacter might reduce test scores is unclear.
Whether these results could one day help people to increase their verbal and mathematical skills by changing their gut bacterial levels is uncertain. “It is too early to tell whether you could eventually take certain bacteria as a supplement to influence intelligence,” says Wade.
What’s more, the genetic variants involved in the study were less strongly linked to bacterial levels than you would generally like with this kind of analysis, says Wade. “Because we’re massively limited in data on links between genetics and the microbiome, many microbiome studies using this type of analysis are using a much more lenient cutoff for defining that set of genetic variants.” The study was also mainly made up of people of European ancestry, so further research is needed to see if the findings apply to other populations, she says.
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