The microbes in our mouths influence how we digest food, how our immune systems fight off infections and the smell of our breath, and an international team of biologists has uncovered links between those microbes and how we live our lives.
Analyzing the saliva of 63 individuals from Nepal, they investigated differences in the oral microbiomes—community microbes in the mouth—of foragers, hunter-gatherers, farmers and people living in urban environments, as well as factors such as smoking and diet.
"The oral microbiome has been understudied, and most studies of the oral microbiome have been conducted in Western populations," said Assistant Professor Emily Davenport, from Penn State Eberly College of Science, who led the research, in a statement.
"Although we have learned a lot from that, microbiomes look different around the world. By studying how the diversity and composition of the oral microbiome varies with lifestyle in a global context, we can improve our knowledge of how the oral microbiome impacts human health."
The biologists studied the oral microbiomes in the mouths of Chepang people, who are foragers in Nepal; Raji and Raute groups, who are hunters and gatherers that recently settled and began farming; Tharu and Newars people, who have relied on farming for more than 300 years; Nepalis who moved from Nepal to the U.S. within the last 20 years; and a group of Americans of European descent, for comparison.
The scientists said that previous research had compared mouth microbes across different geographies—for example, analyzing the saliva of urban Europeans and foragers on the other side of the world—but in this study, they could separate the differences caused by geography with those caused by lifestyle changes.
They found that the differences in the oral microbiome were relatively subtle between groups. The gut microbiome can change a lot between people and over time, but the scientists wrote that the oral microbiome might be less malleable.
However, there was a gradient of change with the composition of different microbes, from foragers to farmers and then urbanites, supporting the idea that lifestyle plays a role in our mouth microbiomes.
One strain that significantly increased in urban groups was Abopobium, high levels of which are associated with negative health outcomes, such as tooth decay, which can contribute to bad breath.
Other specific lifestyle factors that seemed to play a role in the composition of mouth microbiomes included smoking, and the fiber and carbohydrates they ate.
In particular, there was a notable difference between groups that ate most of their carbohydrates from barley and maize, compared to those who ate more rice and wheat.
Eating barley and maize was associated with better oral microbiome health, with more fiber and less quickly digested starch, whereas rice and wheat led to more salivary amylase: an enzyme that begins to digest starches in the mouth.
They also saw differences depending on whether the Nepali participants chewed nettle.
"It makes sense that different microbes might feed on the different grains in a person's diet, but it's interesting that we also see an association with sisnu, also called nettle," said Davenport.
"Nettle is a fibrous plant often chewed by the foragers in this study, much like people might chew gum. Given its important role in Nepali cuisine, culture and medicine, it's interesting to see it is associated with oral microbes."
Davenport added that continuing to investigate how mouth microbiomes can vary across the world will help scientists better understand what shapes them, and how that impacts human health.
This study was published on November 4, in scientific journal Microbiome, and funded by the National Institutes of Health, Stanford University and New York University Abu Dhabi.
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Reference
Ryu, E. P., Gautam, Y., Proctor, D. M., Bhandari, D., Tandukar, S., Gupta, M., Gautam, G. P., Relman, D. A., Shibl, A. A., Sherchand, J. B., Jha, A. R. (2024). Nepali oral microbiomes reflect a gradient of lifestyles from traditional to industrialized, Microbiome 12(228). https://doi.org/10.1186/s40168-024-01941-7
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