Oral Microbiome

A second microbiome, in constant contact with the gut

The mouth hosts its own distinct microbial community, home to more than 500 types of bacteria, making it the second largest microbial habitat in the body after the gut. The two are physically continuous, connected by the full length of the digestive tract, and they stay in contact constantly. People swallow roughly 1 to 1.5 litres of saliva a day, along with whatever bacteria it carries. A landmark analysis from the Human Microbiome Project found that oral and stool bacteria overlapped in nearly half, 45%, of the people studied, showing that oral-to-gut bacterial transfer is common, not a rare event. Shared genera found in both places include Streptococcus, Veillonella, and Actinomyces, bacteria that are common and mostly harmless residents of the mouth but that behave differently once they establish themselves in the gut.

Source: Can oral bacteria affect the microbiome of the gut?

What happens when the wrong bacteria make the trip

In a healthy gut, stomach acid, bile, and competition from resident bacteria mean most swallowed oral bacteria don't survive the journey or take hold. That protection can break down, and when it does, the consequences have been demonstrated directly. In one study, mice given repeated oral doses of Porphyromonas gingivalis, a bacterium strongly linked to gum disease, went on to show raised blood levels of endotoxin and insulin, along with reduced levels of a protein that holds the gut's lining cells tightly together. That combination, a leakier gut and a low-grade inflammatory state, is a pattern researchers link to metabolic problems well beyond the mouth. Reviews of this research point to links between oral-to-gut bacterial translocation and conditions including inflammatory bowel disease, metabolic syndrome, and liver disease, though for most of these the human evidence is still developing.

A separate, more recent finding adds a common, everyday trigger to this picture. A study found that proton pump inhibitors, a widely used class of acid-reducing medication, measurably increased the amount of oral bacteria found in the gut, likely because they reduce the stomach acid that normally acts as a barrier.

Source: Can oral bacteria affect the microbiome of the gut?

Source: Gut, Proton pump inhibitors alter gut microbiota by promoting oral microbiota translocation: a prospective interventional study

What this means for you

None of this means oral bacteria are inherently dangerous. Most of the time, the barriers between mouth and gut do their job. It does mean that oral health and gut health aren't as separate as they might seem, and that conditions weakening those barriers, from gum disease to long-term acid-reducing medication, are worth being aware of. Good oral hygiene, and raising any long-term reliance on acid-reducing medication with a doctor rather than stopping or continuing it unprompted, are reasonable steps. A varied, plant-rich diet supports both microbial communities at once, which is the same idea behind GutLab, everyday gut health starts with regularly feeding the microbiome a broad range of plant-rich ingredients.