Oral health and systemic disease: why they may be more closely linked than we thought

Graham Lloyd-Jones (GL-J): My research into COVID-19 showed that there is a far stronger connection between oral health and systemic diseases than was previously thought. I became interested in the link between poor oral health – particularly gum disease – and increased risk factors for people to develop more severe COVID-19. The best explanation is that the virus travels from the mouth – leaking through damaged, inflamed gums that can no longer act as a defence barrier – straight into the lungs and blood vessels. With the risk factors for COVID-19 and gum disease being similar, I worked with specialist dentists – who have an interest in the immunity of the mouth and the highly complex structures of the gums – to publish a hypothesis that gum disease is a converging risk factor for severe COVID-19.

I then started to read literature that showed a potential causative link with diabetes, Alzheimer’s disease and heart disease. The biological processes of gum disease involve harmful bacteria in the mouth and the astonishing mechanisms they use to survive, infecting our gum tissues and subverting immune cells in a chronic, long-lasting inflammatory process spanning decades. The key pathological driver is Porphyromonas gingivalis (P. gingivalis).

My research focuses on four main areas: cardiovascular disease; Alzheimer’s disease; diabetes and rheumatoid arthritis. Included in these are pregnancy complications. Most gut diseases are now implicated. The same bacteria can even be found in lung cancer and when I tell my colleagues this, they’re extremely surprised – they had no idea that lung cancer could be about bacteria.

GL-J: The reason P. gingivalis is able to infect our immune cells is closely connected to the choices we make about what we ingest – high sugar diets, junk food, smoking and vaping all contribute to oral dysbiosis, an imbalance of the oral microbiome.
Bacteria that metabolises sugar produces an acidic environment in the mouth that P. gingivalis counteracts by producing ammonia, as it prefers a neutral or slightly alkaline environment. It then uses an enzyme to citrullinate human proteins, a process that is linked to autoimmune diseases like rheumatoid arthritis. P. gingivalis is the only bacteria that does this and it explains its link to autoimmune diseases like rheumatoid arthritis.

Unfortunately, gum disease is seen to be inevitable – 90% of people have gingivitis and over 40% of 30-year-olds have periodontitis – and together, periodontitis and dental decay are the most common diseases in the whole body. It’s a major concern.

While poor oral hygiene plays a part, there is literature that is emphasising the risk of oral dysbiosis more. These risk factors – as well as high alcohol consumption, pregnancy, the menopause and menstruation – all encourage the growth of destructive bacteria.

GL-J: Some researchers are working on an enzyme blocker for P. gingivalis in Alzheimer studies but, although they had some success, it proved to be too toxic. Others are using saliva as a diagnostic test – you can diagnose pancreatic cancer from saliva with 96% sensitivity and 82% specificity, and even determine whether a tumour is malignant or benign from a simple spit sample, which is absolutely amazing. Saliva tests are also being used to diagnose Alzheimer’s disease by looking at lactoferrin, with over 80% accuracy.

Much of the current research focuses on the mechanisms gum-disease bacteria uses to drive disease elsewhere in the body. The bidirectional link between periodontitis and diabetes is now recognised in NICE guidance, although it hasn’t yet translated into ensuring that people with diabetes get access to dental care. Efforts are being made to encourage doctors and dentists to collaborate, as the processes in the mouth and pancreas in type 2 diabetes are part of a vicious cycle. You see the same pattern in Alzheimer’s disease, where low saliva and reduced lactoferrin production promote destructive bacteria in the mouth.

Research has also been done on probiotics, but we need to tread carefully, as this focuses attention on the gut, but we also need to think: “What am I feeding my oral microbiome?” I call this the trombone effect – the mouth is like the mouthpiece of what’s going on in the body – and people are now talking about the mouth/gut/brain or gum/brain axis. The mouth allows bacteria into the body without it being filtered by the liver, and gum disease can result in wounds the size of the palm of your hand. It’s like an open wound we can’t protect, and that’s a good way of looking at gum disease.

GL-J: It’s astonishing how removed we have become from our evolutionary environment. We’ve forgotten how to interact with the land, grow our own food and share it with our communities – and, in the process, we share our bacteria as well. We need to focus on eating real, unprocessed foods, which unfortunately means greatly reducing our intake of anything with added sugar, as well as fermentable carbohydrates that don’t provide nutritional value. Many of the vitamins we ingest – A, B, C, D and K – have a direct impact on oral health, and vitamin deficiency is responsible for gum disease as much as sugar is, so it’s the balance of both.

As mentioned, smoking and vaping are very harmful to the whole microbiome. Vaping is especially worrying as young people take it up without realising its effects on oral dysbiosis. Understanding how smoking gives us disease will be one of the keys to understanding oral/systemic links. The dangers of smoking can’t be explained simply due to inhaling hydrocarbons, as gum disease bacteria is found in lung cancer – so the missing link between smoking and other diseases might be oral dysbiosis.

GL-J: My hope is that medicine and dentistry focus more on the concept of oral systemic disease and the connection between the mouth and the rest of the body.
It needs to become mainstream in our medical and dental schools, and we’re starting to work on a curriculum along those lines.

We also need to change the focus of oral care in hospitals. I’m part of a group of researchers that are preparing to send out a letter to all hospitals from the Chief Medical Officer for England calling for investment in pathways to train staff on implementing oral hygiene assessments. I’m also working with hospitals to improve CQC and NICE standards, so every hospital will be required to invest in oral care. Promoting better oral care is hugely cost-effective overall – it can reduce the time patients spend in hospital and it also results in a dramatical fall in the incidence of hospital-acquired pneumonia, ultimately reducing patient death rates.

It’s extremely difficult to get access to funds that can enable these changes to be put into place in hospitals – even for something that is clearly beneficial and cost-effective. Ultimately, we need to stop seeing dental care as an optional extra and increase government awareness so that free or affordable oral care is available for all.

Increasing people’s awareness of the dangers of poor oral health through public health campaigns is so important – people know that smoking kills, but perhaps we need a campaign to say that gum disease kills too. Caring for the mouth is about caring for the whole body, and understanding that link between oral care and general health is vital.

Dr Graham Lloyd-Jones was interviewed by Ella Day, a freelance journalist.
The article was written by Ella Day and Iona Everson, Group Managing Editor at PMGroup.