The Oral Microbiome

Oral microbiome systemic health

The Oral Microbiome

This article summarises some of the research on the role our oral microbiome plays in both oral health, and most importantly our systemic health.

Microbes appear in every corner of human life, and microbes affect every aspect of human life (4).


MicrobiomeThe oral cavity is inhabited by a variety of microorganisms, their control aids in stabilising oral and systemic disease. The above image, summarises what conditions/organs/glands have been associated with the oral microbiome.

P Marsh (2018) explained it well by stating that “the oral microbiome is natural, and has a symbiotic relationship with the host (us) by delivering important benefits. In oral health, a dynamic balance is reached between the host, the environment, and the microbiome. However, the frequent intake of sugar and/or reductions in saliva flow results in extended periods of low pH, which disrupts this symbiotic relationship. Such conditions inhibit the growth of beneficial species and drive the selection of bacteria with an acid-producing/acid-tolerating phenotype, thereby increasing the risk of caries (dysbiosis).”

There is a very important point here – reduced saliva flow.

If you are a ‘mouth breather’ (a big clue being you wake up with a dry mouth) you are at greater risk of imbalances in the oral microbiome due to a lack of saliva flow. Saliva has a key role to play in regulating a healthy oral microbiome – it has anti-bacterial properties!

Significant evidence supports an association between periodontal pathogenic bacteria and preterm birth and preeclampsia (1).

How Does The Oral Microbiome Effect The Entire Body?

It is thought that the inflammation associated with periodontitis (gum disease) leads to the loss of connective tissues and bones. This then allows for the infiltration of inflammatory cells in the connective tissue near the periodontal pocket epithelium.

It is generally believed that this low-grade inflammation will negatively impact the health of the whole body or/and worsen other systemic diseases already present.

Researchers now believe that, in the general population, chronic periodontitis may be an important source of invisible peripheral inflammation. Thus, periodontitis is also called “low-grade systemic disease”, affecting a variety of systemic diseases.

What proportion of the population have periodontist? Some have estimated over 40%!

Oral Microbiome And Gut Health

One possible pathway that oral microbes impact on the gut is simply through swallowing them. The oral bacteria “invade the intestines”, causing imbalances in the gut microbiome and affecting organs of the digestive system. (source)

It has been shown that the colonisation of bacteria from the mouth in the gut affects the metabolism of butyrate.

Another possible pathway is via the blood stream. Oral bacteria, especially periodontitis pathogens, can enter the bloodstream through damaged tissue where they then enter systemic circulation. This is how they may affect the whole body.

For example, Fusobacterium nucleatum colonises the intestine via the blood.

One of the mechanisms by which these oral bacteria trigger systemic inflammation is via their metabolites. They can interact with receptors on our immune cells and trigger an inflammatory response.

There is also research discussing the role of the oral microbiome as a potential cause of SIBO also.

Oral Microbiome And Alzheimer’s

There is a significant correlation between oral health and Alzheimer’s. Let’s look at the evidence.

In one study, 152 people were followed for 20 years. The results found that the severity of periodontitis and the cognition level had an inverse relationship in subjects with fewer than 10 teeth missing. (source) The more teeth we’re missing the greater the risk of cognitive decline – this makes sense based on what we have already discussed regarding how the oral microbiome affects systemic health.

Another longitudinal aging cohort study of 144 people showed that those with the APOE-ε4 gene, and fewer teeth, have a faster cognitive decline than people without these two risks. (source)

One study conducted a 32-year survey of 597 participants (all male). The results showed that tooth loss, the depth of periodontal pockets, and the degree of alveolar bone loss were related to cognitive impairment, particularly in those older than 45. (source)

A survey of 5468 subjects found that irregular tooth brushing was associated with Alzheimer’s disease. (source)

A survey of 2355 people (60 years and older) found that there is an association between periodontitis and cognitive impairment (source)

Oral Microbiome & Cancers

The presence of elevated numbers of certain oral bacteria, particularly P. gingivalis, as well as elevated levels of blood serum antibodies, against this bacterial species, was associated with a higher risk of pancreatic cancer and liver cirrhosis incidence. Attempts are increasingly directed towards investigating the composition of oral microbiome as a simple diagnostic approach in multiple diseases, including pancreatic and liver pathosis (3).

Oral Health, Mastication & Cognitive Health

We also need to be mindful of how mastication and poor oral health can influence the ageing process, both directly and indirectly. Miquel et al (2018) discussed the current evidence and suggested that a deterioration in mastication and oral health during aging can have:

  1. Direct effects on systemic health through mechanisms such as the migration of the oral microbiota into the systemic environment (i.e oral bacteria in to the blood stream)
  2. Indirect effects on systemic health through changes in nutrient intake.

They went on to say that a loss of teeth and reduction in masticatory efficiency during aging can have:

  1. Direct effects on cognitive performance and potentially impact cognitive health through mechanisms such as enhanced adult hippocampal neurogenesis
  2. Indirect effects on cognitive health through changes in nutrient intake.

Miquel et al concluded that “oral health and masticatory efficiency are modifiable factors which influence the risk poor cognitive and systemic health during aging, although it is currently premature to propose chewing-based interventions to slow the rate of cognitive decline and improve cognitive health during aging” (2).


As Pete Williams discussed on the Heapthpath podcast we are more microbe than we are human. And thus to understand ourselves, to understand how we can support someone back to optimal health we need to understand their microbes. It seems, more now than ever before, that the oral microbiome is just as important as the gut microbiome. One paper summed it up well:

Studies in oral microbiomes and their interactions with microbiomes in variable body sites and variable health condition are critical in our cognition of our body and how to make effect on human health improvement (4).

Testing The Oral Microbiome

Invivo Diagnostics offer an oral microbiome test. Contact me if you are interested in ordering this test.

Recommendations For A Healthy Oral Microbiome

  • Focus on the traditional oral hygiene practices – brush twice a day, floss daily. Consider the quality of your toothpaste. My two favourites are: Dentalcidin and Periobiotic.
  • Eat a diet rich in phytonutrients: plenty of fresh and ideally in season fruit and vegetables.
  • If you have periodontitis, or receding gums, consider eating 2-3 meals per day, with no snacking. Listen to episode 36 of The Alex Manos Podcast (see below) for further details on this recommendation. I would also recommend speaking with a qualified nutritional therapist/functional medicine practitioner before starting this however.

Recommended Book


  • Oral Dysbiosis in Pancreatic Cancer and Liver Cirrhosis: A Review of the Literature: click here.
  • A practical guide to the oral microbiome and its relation to health and disease.: click here.
  • The oral microbiome and human health: click here.
  • In Sickness and in Health-What Does the Oral Microbiome Mean to Us? An Ecological Perspective: click here.
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