The Microbes Crawling Around in Your Mouth Might Be Helping to Power Your Brain

3 min readHere’s what you’ll learn when you read this story:Some microbes that live in the mouth can convert nitrates from food into nitrites, which then help create the nitric oxide that widens blood vessels in the body and brain. Researchers wanted to see whether higher nitrate and nitrite levels from certain species of bacteria influenced cognitive performance in people from two different countries. Location shaped the microbiomes and age drove cognition most, but some bacteria still appeared to help.For information to be processed by the biological computer otherwise known as the human brain, neurons constantly need to transmit messages to one another, but there are some other and often unexpected things that can boost that computer’s performance. Maybe one of the strangest (and possibly creepiest) are the microbes crawling around in your mouth.Brain function also depends on blood flow. Nitrates in some foods can be converted to nitric oxide, which increases flow by widening blood vessels throughout the body, including the brain. When you eat beets or something else high in nitrates, most of the nitrate enters your bloodstream, but some ends up back in the mouth for a reason. It’s there that hordes of microbes on your tongue begin to convert it into nitrite, which the body can use to produce molecules of nitric oxide. That’s why researcher Joanna E. L’Heureux of the University of Exeter wanted to investigate how populations of oral bacteria affect information processing, attention, emotion recognition, and memory in both younger and older adults.L’Heureux recruited healthy subjects from the U.K. and Belgium. She was already aware that the older subjects were probably more prone to declining brain function, regardless of microbial activity and nitrate levels. But she still wanted to see how those factors affected cognition. Participants provided saliva samples so the researchers could study the various species of bacteria living in their mouths and assess levels of salivary nitrate and nitrite. Participants also gave blood samples, from which the researchers extracted plasma to measure how much nitrate and nitrite reached the bloodstream. L’Heureux also predicted that microbiomes would differ by region, since the environment determines which species of oral bacteria are present. Those regional differences could reveal which microbes affect a certain population.“Although age-related changes in the oral microbiome and geographical variation in microbial composition have been described independently, it remains unclear whether age-related microbial patterns and their associations with cognitive performance are reproducible across geographically distinct populations,” she said in a study recently published in PLoS One.Along with the saliva and blood samples, subjects took a series of tests gauging brain function and cognition, including abstract reasoning, attention, memory, risk decision making, sensorimotor speed, and spatial orientation. Location determined which cognitive abilities each microbial species affected. In Belgium, Haemophilus parainfluenzae tracked with faster reaction times and higher accuracy on one test. In the U.K., the same bacteria tracked with slower reaction times on that test but faster reaction times on another. Prevotella histicola also gave U.K. participants a reaction-time advantage. In the U.K., Fusobacterium periodonticum and Prevotella jejuni predicted lower accuracy and slower reaction times. In Belgium, Veillonella atypica and Neisseria subflava predicted the same deficits.The oral microbiome was not the only factor influencing the nitrate and nitrite levels that expand blood vessels. Plasma analysis showed that in both Belgium and the U.K., younger adults carried higher nitrite levels than older adults. U.K. participants also showed higher overall nitrite concentrations, despite age and age-related microbiome differences. Age, however, did not affect the relationship between test performance and nitrate and nitrite levels in either location, even though the British and Belgian microbiomes clearly differed. Those species differences aside, the researchers identified no consistent patterns linking the bacteria to cognitive performance. Neisseria flavescens was the only constant across both countries, and younger adults harbored more of it.In the end it was age that predicted cognitive performance more than anything else. As age increased, accuracy, cognitive scores, and reaction time decreased. While Prevotella histicola was correlated with faster reaction times in both geographical groups, and Haemophilus parainfluenzae had a connection to cognitive performance, L’Heureux recognizes further studies are needed to elucidate whether these species actually improve cognition.“Further research should include a more comprehensive assessment of participant characteristics and consider collecting samples on multiple days,” she said. “Despite [uncertainties], significant age and location-related differences were still observed, suggesting that the main findings were robust.”Elizabeth Rayne is a creature who writes. Her work has appeared in Popular Mechanics, Ars Technica, SYFY WIRE, Space.com, Live Science, Den of Geek, Forbidden Futures and Collective Tales. She lurks right outside New York City with her parrot, Lestat. When not writing, she can be found drawing, playing the piano or shapeshifting.