Are you aware of the growing links between the bacteria in our mouths and the risks of colon, breast, pancreatic, and lung cancer? How about dental links with Alzheimer’s disease, pneumonia, inflammatory bowel disease, type 2 diabetes, heart disease and strokes?
One of the necessary evils of scientific inquiry is the need to break massive systems down into component parts and categories. In medicine this leads to small fiefdoms controlled by the likes of cardiologists, pulmonologists, and even neuropsychopharmacologists. Primary care docs like me think we practice at the crossroads of all specialities, and indeed we do in many ways. But when studies come out bridging medicine, dentistry, and personal hygiene — it makes us realize how incredibly complex the universe within really is.
I’m guessing you already knew about dental problems being linked to heart disease. But there is so much more. First some background. Next some studies. Then some useful, actionable stuff we can recommit to in terms of dental health, diet, and diligent hygiene. I’ll even get a little crazy and reference a previous post I wrote about how to avoid or reduce the microplastics and PFAS released with brushing and flossing.
They say don’t look a gift horse in the mouth. But it turns out that we medical doctors should be giving the gift of an oral examination and education to our patients much more thoroughly.
And educating ourselves.
The mouth-body continuum: how oral health impacts our overall health
Part I: The emerging link between oral bacteria and colorectal cancer
I happened upon a study recently that triggered this whole post. It dove deeply into some fascinating research uncovering connections between our oral microbiome and colorectal cancer (CRC) risk. I will include links to this study and all other references used to write this post soon in the comments section… but I’m writing this offline while flying in a plane and hyperlinks are presently a pain.
But the sum of the evidence is becoming increasingly compelling: the trillions of microbes inhabiting our mouths aren't just passive residents—they play an active role in either promoting or protecting against one of the most common cancers worldwide.
The bacterial villains in our mouths
Several oral bacterial species have been identified as potential drivers of colorectal carcinogenesis:
Fusobacterium nucleatum has emerged as a major player, found in 30-50% of colorectal tumors.Recent research has identified a specific subtype called Fna C2 that appears particularly concerning. This bacterial strain:
-
Survives the harsh acidic environment of the stomach
-
Activates growth-promoting signals in colon cells
-
Produces compounds that suppress the local microenvironment immune system
-
Increases oxidative stress and DNA damage via reactive oxygen species released
-
Increases adenoma/precancerous lesion formation by 2.5 times compared to controls.
Streptococcal species commonly found in the mouth, including S. anginosus and S. gallolyticus, also appear to play potentially harmful roles by:
-
Producing enzymes that break down protective tissue barriers in the colon
-
Activating inflammatory pathways that create a tumor-friendly environment
-
Metabolizing dietary nitrates into carcinogenic N-nitroso compounds
Prevotella intermedia contributes to the problem by helping cancer cells hide from the immune system, inducing expression of PD-L1, a protein that acts like an "invisibility cloak" for tumor cells.
Protective bacterial allies
Some oral and gut microbes appear to protect against colorectal cancer:
Lachnospiraceae family bacteria produce butyrate, a compound that promotes colon health by inducing the death of cancerous cells and competing with harmful species like F. nucleatum for space on the colon lining.
Fusobacterium periodonticum, unlike its troublesome cousin F. nucleatum mentioned above, actually helps regulate inflammation. It promotes the development of regulatory T-cells that keep the immune system balanced.
Transmission routes: how oral bacteria reach the colon
You might wonder how bacteria from your mouth make their way to your large intestine. There are several routes, including the most obvious:
-
Swallowing: We swallow at least 150 billion oral bacterial cells every day
-
Bloodstream: Routine activities like chewing or dental procedures can allow bacteria to enter the bloodstream, though it’s a tricky maze to end up in the colon from here.
-
Biofilm formation: Once in the colon, oral bacteria can form resilient communities that are difficult to eliminate
Part II: The broader oral-systemic health connection
That colorectal cancer connection is just one example of how oral health impacts systemic health. As we zoom out to look at the bigger picture, the evidence for oral-systemic links becomes even more compelling.
Cardiovascular disease risk reduction
Poor oral health, particularly periodontal disease, shows strong associations with cardiovascular conditions through multiple mechanisms.
-
Primary prevention: Each additional regular daily brushing session reported reduces cardiovascular event risk by 9%
-
Combined hygiene practices: Brushing twice daily plus regular flossing lowers cardiovascular mortality risk by 51%
-
Periodontal therapy: has been shown to reduce inflammatory markers like CRP by 0.5 mg/L and fibrinogen by 0.14 g/L. In other studies, such reductions of biomarkers have been to 15-20% lower CVD risk.
For patients already diagnosed with coronary artery disease, intensive oral hygiene has been shown to reduce cardiovascular mortality risk by up to 50%.
Stroke prevention
Recent research has identified a particularly striking connection between flossing and stroke risk:
-
Flossing at least once weekly is linked to a 22% lower risk of ischemic stroke
-
44% lower risk of cardioembolic stroke
-
12% lower risk of atrial fibrillation
Diabetes management
The relationship between diabetes and oral health is bidirectional:
-
Periodontal treatment can improve HbA1c levels by 0.8% in diabetic patients (p<0.01). That’s like adding another medicine, or losing significant weight.
-
Oral health coaching reduced HbA1c twice as effectively as standard care (0.8% vs 0.4%) in one study (again, will post links in the comments when I’m settled!)
-
Conversely, uncontrolled diabetes worsens periodontal disease, creating a potentially dangerous cycle
Pneumonia/respiratory protection
Oral hygiene plays a significant role in respiratory health, too:
This would be particularly important for vulnerable populations like the elderly or immunocompromised who are at higher risk of pneumonia. As I wrote this section on the plane I actually aspirated some water down the wrong pipe, unleashing a coughing fit. Other passengers may have slightly regretted that they chose not to wear a mask as I struggled to stop hacking.
No worries. I had one on of course. Source controlled.
Neurological risks
It’s always cool to find little tricks that might help preserve our brains. As I close in upon a half century of existence, I understand how important mental faculties are to a meaningful good health span. I’ll be getting that shingles vaccine because it prevents shingles, and might just reduce our risk of dementia! So too with good dental health it would seem. Systematic reviews identify strong associations between:
Cancer associations beyond the colon
Remember that discussion of Fusobacterium associations with higher risk of incident and more aggressive colon cancer? Well, meta-analyses confirm elevated risks for several other cancers with poor oral health. Here’s a sample, but I think there are almost certainly more. And while correlation does not always equal causation, consistent correlation does deserve our attention and further study:
-
Pancreatic cancer: 56% increase with periodontal disease
-
Lung cancer: 43% higher incidence in edentulous patients
-
Breast cancer: 22% risk elevation with periodontitis
Inflammatory conditions
Sometimes associations with treatment can allow us to retrofit more evidence of links between oral and systemic health. Periodontal therapy demonstrates significant benefits for inflammatory conditions, including;
Part III: Practical steps to reduce our risk
Given the extensive evidence (of admittedly varying rigor) linking oral health to systemic disease risk, what practical steps can we take to protect ourselves? Here’s the obvious, and the overlooked.
Prioritize oral hygiene
It’s 12:41 AM. You have to be up in about six hours and 19 minutes to start the morning fire drill. You’re so damn tired that the idea of brushing well and flossing properly looms larger than a Sisyphean rock candy mountain. But somehow you heroically raise that heavy brush to your mouth. You wrap the floss around your finger like a tourniquet and get down to the final business of a very long day.
The evidence clearly shows that consistent oral hygiene practices are worth the tedious effort. Here is a sort-of-ranked list of measures that will reduce medical illnesses associated with poor oral hygiene, even as they primarily care for our teeth and gums:
Daily Brushing with Fluoride Toothpaste
-
Brushing twice daily with fluoride toothpaste is the cornerstone of oral hygiene, reducing plaque, bacteria, and inflammation. Recall that each additional daily brushing session reduces cardiovascular event risk by 9% and improves overall oral health significantly.
-
Don’t forget that other big number, too. Brushing twice daily plus regular flossing was associated with a 51% reduction in cardiovascular mortality risk.
Daily Flossing or Interdental Cleaning
-
Flossing reduces risks of systemic diseases like ischemic stroke by 22% and cardioembolic stroke by 44%, as it removes bacteria and debris from between teeth that brushing cannot reach.
-
Approximately 37% of Americans report flossing once weekly, while nearly 32% admit they don't floss at all.
Routine Professional Dental Care
Periodontal Therapy for Gum Disease Management
Healthy Diet
-
A diet like the Mediterranean diet, rich in antioxidants, Omega-3 fatty acids, and fiber supports gum health and reduces systemic inflammation, lowering risks of periodontal disease and associated conditions like cardiovascular disease.
-
Fiber: Consuming at least 30 grams daily can double the abundance of protective Lachnospiraceae bacteria
-
Low fiber intake reduces butyrateproduction, enabling Streptococcus overgrowth which was linked with CRC.
-
Polyphenol-rich foods: Pomegranates, berries, and green tea contain compounds that inhibit harmful bacterial biofilms
-
Omega-3s: Fish, nuts, seeds, etc have been shown to help reduce bacterial adhesion to colonic mucosa
-
Limit red meat and saturated fats: These foods can enhance the virulence of cancer-associated bacteria. Specifically, red meat-derived heme iron upregulates F. nucleatum’s fadA virulence gene
-
Saturated fats increase secondary bile acids (e.g., deoxycholic acid), which promote Prevotella species-driven inflammation
Avoiding Tobacco Use
Mouthwash Use
-
While mouthwash can help reduce bacterial load, its impact on systemic disease prevention seems to be less significant compared to mechanical cleaning methods like brushing and flossing from what I could find.
-
However, I did find one study that used a mouthwash with 0.2% chlorhexidine at least 3 times weekly, and found an associated decrease in colorectal cancer incidence over 10 years (19% relative risk reduction). Addendum: a friend who is a dentist added this bit via email that I thought I should share: “This was a really great article. Chlorhexidine rinses shouldn’t be used longer than 2 weeks though bc it will stain teeth brown. There is an also a lot of promising research coming out in the dental community on the positive oral and systemic effects of Xylitol.”
-
Addendum re: xylitol. A really quick online search provides food for thought. “Xylitol has been shown in clinical studies to reduce dental caries by inhibiting the growth of Streptococcus mutans bacteria and decreasing plaque formation. Research indicates xylitol can help prevent acute otitis media (middle ear infections) when delivered through gum or lozenges. Some preliminary studies suggest xylitol may positively impact bone density and gut health, though more research is needed to confirm these systemic benefits.“
-
Most mouthwashes contain alcohol, which is less than ideal for mucosal surfaces inside the mouth. That alcohol burn is causing a little superficial damage each time. They do make zero alcohol mouthwash, and I’m pretty sure my dentist recommends that instead.
Drinking Fluoridated Water
Techniques and tools
Overlooked ideas about brushing, flossing, swishing and spitting can be further reviewed in this post I wrote a while back. I never really considered the micro- and nanoplastics that brushing with nylon bristles surely creates, nor the forever chemical PFAS that help many brands of dental floss slip in between your teeth. I’m loyal to one brand of floss that avoids all these problems, and cuts down on the billions of miles of plastic floss we unravel into oblivion each year on planet Earth.
But I still refuse to use horse hair toothbrushes.
Conclusion
We already knew that good oral health is tied to good cardiovascular health, but increasingly we are finding it does not end there.
Brushing, flossing, probably some mouth wash, regular dental care, dental therapies when needed, healthy diets that minimize junk and refined carbs/sugars while emphasizing fiber and nutrients, and I wager reducing microplastics and PFAS in our gums and beyond should all combine to reduce our risks of systemic diseases ranging from colon cancer to dementia.
Kind of makes you want to go brush your teeth. Now. Doesn’t it?
Take good care.
And floss.
No really.
Floss😁
—————————
This entry was first published on Substack, where I write about vital and overlooked ideas your family doc might share — if only we had more time. Add your email to the list and you won’t miss future posts. Amazing horse photo credit Michael Kristenson.
