The Theory: How Oral Disease Might Cause Cancer

Science doesn't know how oral disease is related to cancer. But we've seen enough math over the past decade or so of study to know that there's definitely something going on in your mouth that can make you vulnerable to cancer -- even decades later. We're going to lay out the most commonly-accepted theory for you.

The Inflammation Theory

The mouth is a place of almost constant microscopic injuries. For example, something as simple as eating popcorn can cause hundreds of tiny scrapes and cuts on the gums and roof of the mouth. Furthermore, the inside of the mouth is naturally home to hundreds of kinds of bacteria and microbes -- some of which the body considers hostile. When those hostile microbes get into those tiny injuries, it causes a low-grade infection that can literally last for years if you keep re-scraping up the inside of your mouth.

That infection, in turn, leads to a constant low-grade inflammation. Inflamed cells don't respond as well to normal inter-cellular chemical signals, including the signal that tells the cell to die if it starts to act abnormally. If something unusual happens to a cell that causes it to act like a cancer cell, and then the normal self-protection message fails to kill the cell, it can become cancerous. Thus, oral bacteria act as an enabler of carcinogenesis.

The major flaw in this theory is that it doesn't explain why one of the inflamed cells may start to act like a cancer cell. It assumes that, essentially, cells in your body are constantly 'going rogue', starting to act like cancer cells, and then getting killed by your own body. Interestingly, this is another commonly-accepted theory about how cancer works, but when you build one theory on top of another unproven theory, you have to take the whole thing with several grains of salt.

That doesn't mean that there's a flaw in the math -- there's definitely a relationship between oral disease and cancer -- it just means we don't know exactly why.

Getting Into the Data: In Depth On Oral Bacteria and Cancer

Last week we put up several links to studies that show a pretty clear link between oral bacteria and cancer. We couldn't help but think that perhaps it would be helpful to some of you if we translated at least one of them from scientific jargon into layman's English. From The Journal of Oral Microbiology:

"Inflammation caused by infections may be the most important preventable cause of cancer in general. However, in the oral cavity the role of microbiota in carcinogenesis is not known. Microbial populations on mouth mucosa differ between healthy and malignant sites and certain oral bacterial species have been linked with malignancies but the evidence is still weak in this respect. Nevertheless, oral microorganisms inevitably up-regulate cytokines and other inflammatory mediators that affect the complex metabolic pathways and may thus be involved in carcinogenesis. Poor oral health associates statistically with prevalence of many types of cancer, such as pancreatic and gastrointestinal cancer."

What this says, in short, is that many cancers are indirectly caused by infections -- indirectly because it's not the infection itself that causes the cancer, but instead the inflammation caused when your body fights the infection. In addition, this is inflammation that certain bacteria in your mouth can make much, much worse. We haven't figured out exactly how these bacteria cause cancer, so we can't say for certain that they do -- but the statistical correlation between oral health and cancer risk is quite significant.

"Our unpublished results from a cohort study in Sweden with 16 years of follow-up showed that age, female gender, and periodontitis with loss of the first mandibular molars were the principal independent predictors of cancers in general, and breast cancer in particular, as registered in the Swedish Cancer Registry. From the same database, premature death of young individuals was observed to link statistically with periodontitis and missing molars whether the cause of death was because of cancer, cardiovascular, or gastrointestinal disease."

This is the quote we referred to in this months' newsletter. Translated, it says that there are three factors that are the most correlated with breast cancer. The first is the age of the person. The second is their gender. The third is whether or not they had periodontal disease when their first molars were removed.

Why is this considered just as relevant as age and gender? Because it's statistically correlated to an extraordinary degree; if you had periodontal disease when your first molars came out, you were much more likely to get breast cancer. It’s not quite the difference between getting breast cancer as a man and getting breast cancer as a woman, but close to the difference between getting it as a 25 year old and getting it as a 35 year old.

The Hard Science of Soft Sciences

Here at Drs. Eric Johnson and Tom Risbrudt's office, we spend a small but significant portion of our time keeping up on the latest in dental research, from the cutting-edge (no pun intended) pharyngeal surgeries out of Switzerland to the UC Berkeley medical students pumping out research papers about the effects of non-fluoride toothpaste. As mentioned last month, one of the things we see more and more is that there really isn't a distinction between oral health and general health. If your mouth is unhealthy, your body will be too, and vice versa.

But there's a kind of problem with biological sciences. They're referred to by some as 'soft' sciences, because there are just so many variables involved with any form of life that two seemingly identically sets of circumstances can come up with radically different results (ask the scientists studying which diets are best for fat loss!) So a single study that says 'oral bacteria are linked to increased pancreatic cancer risk' is interesting, but until four or five other groups have come up with studies saying the same thing, that's all it is -- interesting.

As it happens, however, the link between breast cancer and oral health isn't just a one-off event. It's been shown in several studies from all over the world:

• The Journal of Oral Microbiology
• Medical News Today
• The Journal of Translational Medicine
• Journal Portal of Shahid Beheshti Medical University

So we at Drs. Eric Johnson and Tom Risbrudt's office are very confident that, when we say that we're doing our part to help fight cancer, we mean it. Not only did our team support the Support G. Komen Walk for the Cure, we also participated in the event last month. We know that the work we do right here every day -- keeping people's mouths healthy -- helps reduce their risk of cancer as well.

 That feels pretty darn good.