The Health of Your Mouth May Affect Your Risk of Colorectal Cancer

Could the health of your mouth, gums, and teeth influence the likelihood of developing cancer or make tumors grow more aggressively? A growing body of evidence suggests that the presence of gum disease is linked with an increased risk of several types of cancer, especially colorectal and pancreatic cancer. Gum disease is a set of inflammatory conditions affecting the tissues surrounding the teeth.

The Mouth Is the Second Largest Microbiome in the Body

The mouth’s microbiome and the balance of bacteria within it influences overall health in many ways, says Mingyang Song, ScD, an associate professor of clinical epidemiology and nutrition at the Harvard T.H. Chang School of Public Health in Boston. Dr. Song has published research on the connection between the oral microbiome and colorectal cancer.

Researchers have zeroed in on a few bacteria that may be especially important in terms of health, including Fusobacterium nucleatum, which is normally found in low levels in the mouth, but can flourish and contribute to inflammation and gum disease. Left untreated, gum disease can eventually lead to destruction of the bone and tissues that support the teeth, causing tooth loss.

Gum Disease and Tooth Loss Linked to Increased Colorectal Cancer Risk

The health of the mouth microbiome has also been linked to a variety of diseases outside of the mouth, including cancer, obesity, diabetes, heart disease, Alzheimer disease, inflammatory bowel disease, rheumatoid arthritis, and metabolic dysfunction–associated steatotic liver disease, says Song. There’s also a relationship to a few types of cancer, including cancers of the head and neck. It's most consistently associated with colorectal and pancreatic cancers, he adds.

But scientists still don’t entirely understand the degree of involvement, if any, that gum disease and the mouth microbiome has in causing these conditions.

A history of gum disease was associated with an 11 percent increased risk of a conventional adenoma, another type of colon polyp that is noncancerous, but can eventually turn into cancer.

In both those studies, the authors pointed to a possible disruption in the mouth microbiome that could be related to poor oral hygiene, genetics, smoking, diabetes and obesity. Compared with healthy individuals, the people diagnosed with colorectal cancer had higher transmission rates of the harmful F. nucleatum from the mouth to the gut.

Imbalances in the Mouth Microbiome Can Cause Inflammation

How does harmful bacteria in the mouth potentially affect other parts of the body, including colorectal cancer? That isn’t totally clear; both direct and indirect ways have been proposed, says Song.

The oral microbes can directly get to the other parts of the body and cause damage and inflammation, he says. “Also, alterations in the oral microbiome can cause systemic inflammation and increase disease risk indirectly.”

How Mouth Bacteria Travels to Other Parts of the Body

And how does the bacteria get to the G.I. tract or the bloodstream? There are a couple of ways that can happen, says Floyd Dewhirst, DDS, PhD, an emeritus professor of oral medicine, infection, and immunity at Harvard Medical School in Boston. Dr. Dewhirst has been studying the mouth microbiome for decades.

“Basically, the fate of almost all the bacteria that live in the mouth is at some point to get swept up by saliva and swallowed,” he says. Following the path down, the bacteria go through the stomach, and if they survive the acid treatment of the stomach, they could make it to the GI tract, says Dewhirst.

There are also lots of bacteria that can cause infection in your periodontal and subgingival pockets (the spaces or openings surrounding the teeth under the gum line and where the tooth connects to the gum) in people who have gum disease, he says.

“When you do things like bite into an apple or brush your teeth, a small number of these organisms are able to get into the bloodstream from the vessels that are next to the gum tissue. Most of the time the body is good at finding the small number of bacteria and destroying it, but occasionally, something that's gotten into the bloodstream can circulate through the body and go somewhere else and start an infection,” says Dewhirst.

You can also spread bugs from your mouth if you get saliva on your fingers and then touch your eye, nose, or scratch broken skin, he says.

Researchers Find a More Dangerous Subspecies of F. Nucleatum

First, researchers did a careful genetic comparison between F. nucleatum from colorectal tumors and those from healthy mouths and learned that one subspecies of the bacteria, called Fna, was more likely to be in colorectal tumors. Further study revealed that there were two distinct types of Fna. Although both types were found in mouths, only one type, Fna C2, was associated with colorectal cancer.

Investigators then infected mice that had inflamed colons with these two types of F. nucleatum. Mice infected with Fna C2 developed more tumors compared with mice infected with the other type.

Although researchers don’t know yet how these bacteria travel from the mouth to the colon, researchers showed that Fna C2 could survive longer in acidic conditions, like those found in the gut, than the other type of Fna. That could mean the bacteria travels along a direct route through the digestive tract, according to the authors.

Knowing the exact bacterial lineage that is associated with colorectal cancer is critical for prevention and targeted treatment to improve outcomes, the authors wrote.

Bottom Line: Practicing Good Oral Hygiene May Reduce Your Risk of Colorectal Cancer

While it isn’t clear how oral hygiene specifically may influence cancer risk, we know that poor oral hygiene increases risk of gum disease, says Song. “Practicing oral hygiene is certainly a good practice,” he says.

Besides that, a healthy diet and lifestyle, including regular exercise and not smoking, has also been shown to keep the oral microbiome healthy, says Song.