New research published in Scientific Reports suggests that microbes in the human gut and mouth can impact how long people live [1].
Bacteria and other microbes are often associated with diseases, but disease-causing microbes are only a minority. The majority of microbes are harmless or beneficial to humans, and we have millions of them living inside and outside us. Researchers refer to this community as the microbiota.
In previous research, scientists had noticed an association between microbiota and longevity [2]. However, the association between two things does not necessarily mean that one is causing the other. Therefore, in this new paper, researchers explored potential causal relationships between gut and mouth microbes’ composition and longevity in order to determine what compositions of microbiota result in increases or decreases in lifespan.
The good, the bad, and the ugly microbes
These researchers conducted a complex analysis that allowed them to define many causal interactions between microbes and longevity. According to their analysis, one of the microbes that positively influenced longevity was gut probiotic bacteria, which impact body fat [3].
One of the microbes in the saliva that was found to increase the odds of living longer is known to reduce the risk of gastric cancer. Different microbes identified in the analysis were also reported in previous research to have a potential negative correlation with congestive heart failure but a positive correlation with longevity. On the other hand, a gut bacterium that negatively influences longevity is also a pathogen that promotes colorectal cancer [4].
In saliva, researchers also identified microbes that decreased longevity. Some of those were known to increase the risk of diseases such as biliary tract cancer, lung cancer, asthma, obstructive pulmonary disease, and osteoporosis. The researchers concluded that decreased longevity could be a result of those diseases.
These researchers also studied people who are expected to live a long time and analyzed which bacteria tended to live in their bodies. The kinds of microbes residing in the long-lived people were associated with plant-rich diets.
On the other hand, microbes linked to a Western diet, high in fat and salt, were not common in those people [5]. Therefore, the authors speculate that long-lived people are more likely to prefer healthy diets rich in complex carbohydrates, fruit, and vegetables instead, which promote the observed microbiotal composition.
Researchers also analyzed microbiota diversity in the gut, saliva, and tongue. An in-depth analysis indicated a causal link between smaller microbes’ diversity and longevity. This result was rather unexpected as previous research had indicated the opposite. Future studies will need to address differences in the results obtained between different research groups.
Same microbes, different outcomes
The authors of this study performed the initial analysis on a Chinese cohort and replicated it on an European cohort. This investigation led to interesting observations.
The researchers identified specific microbes that were negatively correlated with longevity in people from the Netherlands but positively in the Chinese cohort. Other microbes had a negative effect on longevity in Chinese people but had no impact on longevity in Europeans. The researchers also identified groups of microbes that are more abundant in Chinese people who were predicted to live a long time but not in similar Europeans.
Such differences are likely due to different geographical populations’ diets, lifestyles, and genetic backgrounds. However, there is a need for extensive studies with people of varying ethnicities to find specific reasons why such differences exist.
Different outcomes of the same microbes are not limited to different populations. Even the same bacteria on the same person can lead to different outcomes, depending on where in the body they reside.
Researchers identified bacteria associated with decreased longevity when found in the gut. However, they were associated with increased longevity when in the mouth. They point out that it is because some of those microbes are normally part of the mouth microbiota, and that is where they are supposed to be residing. More research is needed to study how microbes spread through different body parts and affect lifespan and health.
Microbes are a piece in the bigger longevity puzzle
Authors mention that previous studies show that some of the most impactful factors influencing longevity are sex, educational level, or diseases. In this study, researchers did not have data regarding economic, behavioral, or environmental factors in the analyzed population. That limits the analysis as researchers couldn’t analyze those factors in connection with the microbial profiles of study participants. Future studies will have to analyze whether such factors influence longevity independent of microbiota.
Literature
[1] Liu, X., Zou, L., Nie, C., Qin, Y., Tong, X., Wang, J., Yang, H., Xu, X., Jin, X., Xiao, L., Zhang, T., Min, J., Zeng, Y., Jia, H., & Hou, Y. (2023). Mendelian randomization analyses reveal causal relationships between the human microbiome and longevity. Scientific reports, 13(1), 5127.
[2] Biagi, E., Franceschi, C., Rampelli, S., Severgnini, M., Ostan, R., Turroni, S., Consolandi, C., Quercia, S., Scurti, M., Monti, D., Capri, M., Brigidi, P., & Candela, M. (2016). Gut Microbiota and Extreme Longevity. Current biology : CB, 26(11), 1480–1485.
[3] Omar, J. M., Chan, Y. M., Jones, M. L., Prakash, S., & Jones, P. J. (2013). Lactobacillus fermentum and Lactobacillus amylovorus as probiotics alter body adiposity and gut microflora in healthy persons. Journal of functional foods, 5(1), 116-123.
[4] Kostic, A. D., Chun, E., Robertson, L., Glickman, J. N., Gallini, C. A., Michaud, M., Clancy, T. E., Chung, D. C., Lochhead, P., Hold, G. L., El-Omar, E. M., Brenner, D., Fuchs, C. S., Meyerson, M., & Garrett, W. S. (2013). Fusobacterium nucleatum potentiates intestinal tumorigenesis and modulates the tumor-immune microenvironment. Cell host & microbe, 14(2), 207–215.
[5] Wu, G. D., Chen, J., Hoffmann, C., Bittinger, K., Chen, Y. Y., Keilbaugh, S. A., Bewtra, M., Knights, D., Walters, W. A., Knight, R., Sinha, R., Gilroy, E., Gupta, K., Baldassano, R., Nessel, L., Li, H., Bushman, F. D., & Lewis, J. D. (2011). Linking long-term dietary patterns with gut microbial enterotypes. Science (New York, N.Y.), 334(6052), 105–108.
