The oral microbiome is a collection of bacterial colonies found in different parts of the mouth, including areas such as the teeth and the tonsils.[1]
The oral microbiome is the second most diverse bacterial environment, only to the large intestine and the colon. In fact, the digestive tract and the mouth combined house around sixty per cent of the total bacteria in our body.[2]
That’s almost seven hundred different species of bacteria all potentially living in your mouth right now.
Why look at this when our website focuses on the brain and the gut connection?
Well, it seems that the health of the oral microbiome is associated with most of the common conditions we see in the brain, the gut and everything in between.
For example, a study from Nature published in 2021 showed the first signals that variations in the oral microbiome are associated with depression in young people.[3]
Broadly, connections between chronic diseases and the oral microbiome are expanding. As of the most recent review I could find at the time of writing this, a review published in March 2022, the oral microbiome is associated with inflammatory bowel disease,[4] cancers,[5] cardiovascular disease,[6] Alzheimer’s disease,[7]diabetes,[8] and rheumatoid arthritis.[9]
This article will explore what’s referred to as the silent epidemic occurring “right under our noses”, the ideas around how the bacterial environment in your mouth causes issues, and some tips to change it.
It all comes down to something called dysbiosis.
Something that occurs commonly in the gut microbiome but also in the mouth too.
If you are new to this, then dysbiosis is the collective term used to describe an imbalance in the composition, distribution and diversity of bacteria in any given environment.[10]
In a healthy bacterial environment, colonies of over 1000 species of bacteria would exist across different regions of a system, for example, the digestive system.
All these bacteria coexist in a balance that, on the surface, is beyond remarkable when you think about it.
In a balanced, healthy state, they provide an immune role, protecting us from foreign bacteria coming in from the outside world. They also police the internal environment, protecting the integrity of the inner bacterial landscape.
That’s not all. Different species of bacteria also help to digest your carbohydrates and turn them into essential energy sources for the digestive system.
Disruption in this balance is called dysbiosis.
Three different types of dysbiosis can occur either together or independently of each other. The first is a loss of beneficial bacteria, the second is an overgrowth of potentially harmful bacteria, and the third is a loss in diversity of the bacterial species.[11]
Something that’s ultimately the most important.
The reason why?
Specific species of bacteria have particular functions which contribute to the overall balance of the bacterial environment, and, in some cases, when they are lost, they are irreplaceable!
One reason dysbiosis within the oral microbiome is such a significant focus is down to what’s called vascularity.
Vascularity describes how much blood flow comes in and out of an area via blood vessels. In the case of the mouth, there is a dense network of both blood vessels and nerves.
This high level of blood flow into the different regions of the mouth means that undesirable, overgrown bacteria that form part of the dysbiotic landscape can leak into the blood flow travelling back into the body—carrying these undesirable bacteria and the inflammation they cause with it.
For example, periodontitis, inflammation of the gums around the teeth, is one of the most common infections on earth. Periodontitis imbalances the bacterial environment to a point where it causes chronic inflammation;[12] this inflammation can be within the mouth and radiate into the rest of the body.
Our understanding of how dysbiosis causes periodontitis and gingivitis is still developing.
The idea that more than one species of bacteria is causing the problem has consensus. But to illustrate how early we are here, the main bacteria, such as Filifactor alocis, P.gingivalis, and T.denticola, all increased in periodontitis, still represent less than four per cent of the total bacteria involved.[13]
Plaque that develops on our teeth is bacteria forming a film to protect itself and, in some cases, spread.
Not all of this bacteria causes problems, so, in some cases, the plaque that develops just requires regular cleaning.
In the case of gingivitis, a milder, reversible infection compared to periodontitis, the bacteria around the teeth colonise. The plaque they form if left untreated slowly causes more and more inflammation.
But how does this plaque develop in the first place?
Early colonisers are species of bacteria that get missed by our toothbrushes. The bacteria Actinomyces starts to develop after six hours and matures over seven days. After twelve weeks, the diversity of the oral microbiome overgrows with predominantly gram-negative bacteria. Bacteria that are often associated with inflammation.
Other causes of plaque you may be more or less familiar with are sugary foods, particularly those high in sucrose,[14] and foods high in starch that change the pH in the mouth, contributing to bacteria and forming plaques.[15]
Oral bacteria can travel and affect our brains.
One of the features of the plaque or biofilm is that bacteria, generally gram-negative bacteria (bacteria that mainly cause inflammation), travel from these bases to other areas of the body.
So if you think of it this way, the more plaque around your teeth, the more bases bacteria have to travel from into your body. Bacteria travelling in this way is called “translocation.”
Translocation and the realisation that bacteria in the mouth is travelling begins to amplify our question for this article, doesn’t it?
A scarier part is that this bacteria transferring into the body is not associated with pain.
Most of the time, you don’t even know it’s happening. Something that seems especially pertinent in Alzheimer’s disease, a condition which, if you didn’t know, begins to develop in some as early as their mid-thirties.[16]
A comparative study between healthy people and people with Alzheimer’s disease found that the brains of those living with Alzheimer’s disease had higher levels of the toxin, gingipain, produced by the oral bacteria P.gingivalis, one of the critical causes of chronic periodontitis.
The toxins from P.gingivalis cause the body to create inflammatory chemicals that result in neuroinflammation during chronic periodontitis.[17]
Combine these results with the early development mentioned above, and it seems that changes for the worse in the mouth, especially when it comes to periodontal diseases, can be seen as early warning signs for Alzheimer’s disease later on.[18]
So I know that dysbiosis in digestion can cause IBS but does dysbiosis in the mouth make it worse?
Great question!
If you’ve read articles on this site about the gut and brain connection, you’ll have heard about the bi-directional nature between the two systems. Simply put, this refers to the fact that it isn’t one-way traffic from gut to brain and vice versa.
Interestingly, a comparison between the microbiome in the digestive system and the mouth found that they were predictive of each other.[19]
Whilst the bacteria differed at the different sites, the broader communities seemed to have common themes. This commonality suggests that if the diversity in one district was affected in one area, such as the oral microbiome, the community in another location, such as the digestive system, may be commonly affected.
How might this happen when it comes to the mouth and the stomach, for example?
One route we’ve discussed that’s via bacteria travelling through the bloodstream and entering the digestive system that way. Another is a little more interesting and involves how many times we swallow.
People swallow about six hundred times a day, roughly equating to around one and a half litres of saliva containing numerous oral bacteria.[20]
Generally, your stomach acid and the immune system in the stomach should be able to burn up these oral bacteria effectively, but what happens if your stomach acid isn’t acidic enough?
People who use proton pump inhibitors or PPI drugs for acidity have this condition, and it’s called achlorhydria. When looking at people who have used long-term PPIs, higher amounts of oral bacteria such as Streptococcus spp and Veillonella spp. These more elevated amounts of oral bacteria can also be worse in people suffering from gastritis or gastric bypass.[21]
Immune suppression caused by aging, drugs, or viral infections can also be responsible for increases in oral bacteria in the digestive system.[22]
How does this contribute to IBS?
Remember that dysbiosis can occur when there are imbalances in the species in specific areas. So if we see more oral bacteria, especially pro-inflammatory ones, pop up in the digestive system, this can fuel the origins of IBS.
So is the mouth a window into your digestive and mental health?
In this article, we have seen how bacteria in the mouth, second only in diversity to the digestive system, can travel to different body parts, such as the brain and digestion and cause numerous issues.
Now there are some simple things to do to remedy this.
The first is to see your dentist if you haven’t in the last six months and get a comprehensive clean that will reset some bacteria-based plaques that can cause these problems.
Before that, if you aren’t, it’s time to brush your teeth twice a day without fail and add some floss in the mix to break up the bacterial communities around the teeth that are building up.
Secondly, observe whether your gums bleed when you brush your teeth or floss. If this happens to you, it’s called “bleeding on probing” in dentistry and is a vital sign that you might be in the early stages of periodontal disease already, and the clock is ticking.
Lastly, take care of your diet. An interesting study found that a stone age diet, presumably similar to the Paleo diet, improved markers of periodontal disease such as the bleeding mentioned above.[23]
Another study confirmed that a diet high in unprocessed complex carbohydrates, vegetable proteins, omega-3 fatty acids, minerals and vitamins improved periodontal inflammation.
In contrast, the same study found that diets high in refined carbohydrates, non-vegetable proteins, pro-inflammatory saturated fats (presumably from junk food), and an unbalanced amount of vitamins and minerals may increase periodontal inflammation.[24]
As always, the power is in your hands!
Hope this helps x
References
[1] Dewhirst FE, Chen T, Izard J, et al. The human oral microbiome. J Bacteriol. 2010;192(19):5002-5017. doi:10.1128/JB.00542-10
[2] NIH HMP Working Group, Peterson J, Garges S, et al. The NIH Human Microbiome Project. Genome Res. 2009;19(12):2317-2323. doi:10.1101/gr.096651.109
[3] Wingfield, B., Lapsley, C., McDowell, A. et al. Variations in the oral microbiome are associated with depression in young adults. Sci Rep 11, 15009 (2021). https://doi.org/10.1038/s41598-021-94498-6
[4] Read E, Curtis MA, Neves JF. The role of oral bacteria in inflammatory bowel disease. Nat Rev Gastroenterol Hepatol. 2021;18(10):731-742. doi:10.1038/s41575-021-00488-4
[5] Tuominen H, Rautava J. Oral Microbiota and Cancer Development. Pathobiology. 2021;88(2):116-126. doi:10.1159/000510979
[6] Humphrey LL, Fu R, Buckley DI, Freeman M, Helfand M. Periodontal disease and coronary heart disease incidence: a systematic review and meta-analysis. J Gen Intern Med. 2008;23(12):2079-2086. doi:10.1007/s11606-008-0787-6
[7] Sureda A, Daglia M, Argüelles Castilla S, et al. Oral microbiota and Alzheimer’s disease: Do all roads lead to Rome?. Pharmacol Res. 2020;151:104582. doi:10.1016/j.phrs.2019.104582
[8] Matsha TE, Prince Y, Davids S, et al. Oral Microbiome Signatures in Diabetes Mellitus and Periodontal Disease. J Dent Res. 2020;99(6):658-665. doi:10.1177/0022034520913818
[9] Tong Y, Zheng L, Qing P, et al. Oral Microbiota Perturbations Are Linked to High Risk for Rheumatoid Arthritis. Front Cell Infect Microbiol. 2020;9:475. Published 2020 Jan 22. doi:10.3389/fcimb.2019.00475
[10] DeGruttola AK, Low D, Mizoguchi A, Mizoguchi E. Current Understanding of Dysbiosis in Disease in Human and Animal Models. Inflamm Bowel Dis. 2016;22(5):1137-1150. doi:10.1097/MIB.0000000000000750
[11] DeGruttola AK, Low D, Mizoguchi A, Mizoguchi E. Current Understanding of Dysbiosis in Disease in Human and Animal Models. Inflamm Bowel Dis. 2016;22(5):1137-1150. doi:10.1097/MIB.0000000000000750
[12] Scannapieco FA, Dongari-Bagtzoglou A. Dysbiosis revisited: Understanding the role of the oral microbiome in the pathogenesis of gingivitis and periodontitis: A critical assessment. J Periodontol. 2021;92(8):1071-1078. doi:10.1002/JPER.21-0120
[13] Griffen AL, Beall CJ, Campbell JH, et al. Distinct and complex bacterial profiles in human periodontitis and health revealed by 16S pyrosequencing. ISME J. 2012;6(6):1176-1185. doi:10.1038/ismej.2011.191
[14] Atkinson FS, Khan JH, Brand-Miller JC, Eberhard J. The Impact of Carbohydrate Quality on Dental Plaque pH: Does the Glycemic Index of Starchy Foods Matter for Dental Health?. Nutrients. 2021;13(8):2711. Published 2021 Aug 6. doi:10.3390/nu13082711
[15] Atkinson FS, Khan JH, Brand-Miller JC, Eberhard J. The Impact of Carbohydrate Quality on Dental Plaque pH: Does the Glycemic Index of Starchy Foods Matter for Dental Health?. Nutrients. 2021;13(8):2711. Published 2021 Aug 6. doi:10.3390/nu13082711
[16] Viña J, Sanz-Ros J. Alzheimer’s disease: Only prevention makes sense. Eur J Clin Invest. 2018;48(10):e13005. doi:10.1111/eci.13005
[17] Ding Y, Ren J, Yu H, Yu W, Zhou Y. Porphyromonas gingivalis, a periodontitis causing bacterium, induces memory impairment and age-dependent neuroinflammation in mice. Immun Ageing. 2018;15:6. Published 2018 Jan 30. doi:10.1186/s12979-017-0110-7
[18] Kaliamoorthy S, Nagarajan M, Sethuraman V, Jayavel K, Lakshmanan V, Palla S. Association of Alzheimer’s disease and periodontitis – a systematic review and meta-analysis of evidence from observational studies. Med Pharm Rep. 2022;95(2):144-151. doi:10.15386/mpr-2278
[19] Ding T, Schloss PD. Dynamics and associations of microbial community types across the human body. Nature. 2014;509(7500):357-360. doi:10.1038/nature13178
[20] Kitamoto S, Nagao-Kitamoto H, Hein R, Schmidt TM, Kamada N. The Bacterial Connection between the Oral Cavity and the Gut Diseases. J Dent Res. 2020;99(9):1021-1029. doi:10.1177/0022034520924633
[21] Kitamoto S, Nagao-Kitamoto H, Hein R, Schmidt TM, Kamada N. The Bacterial Connection between the Oral Cavity and the Gut Diseases. J Dent Res. 2020;99(9):1021-1029. doi:10.1177/0022034520924633
[22] Crakes KR, Jiang G. Gut Microbiome Alterations During HIV/SIV Infection: Implications for HIV Cure. Front Microbiol. 2019;10:1104. Published 2019 May 22. doi:10.3389/fmicb.2019.01104
[23] Baumgartner S, Imfeld T, Schicht O, Rath C, Persson RE, Persson GR. The impact of the stone age diet on gingival conditions in the absence of oral hygiene. J Periodontol. 2009;80(5):759-768. doi:10.1902/jop.2009.080376
[24] Santonocito S, Polizzi A, Palazzo G, Indelicato F, Isola G. Dietary Factors Affecting the Prevalence and Impact of Periodontal Disease. Clin Cosmet Investig Dent. 2021;13:283-292. Published 2021 Jul 9. doi:10.2147/CCIDE.S288137
