The Gum Bacterium in 96% of Alzheimer's Brains | The Starved Brain, Chapter 8

Gum disease and dementia

Gum Disease and Dementia: What Is Proven and What to Measure

Severe gum disease is tied to dementia; mild gum disease is not. Pooled studies found close to three times the odds of dementia with severe periodontitis and no measurable excess below moderate disease, and no one has shown that treating gum disease prevents dementia.

A bacterium from bleeding gums turns up in most Alzheimer’s brains, and in plenty of healthy ones too. Reading that evidence correctly changes what you should worry about and what you should ask for.

Is gum disease and dementia a real connection or a scary headline? The honest answer is both, depending on which gums and which claim. The chapter video, The Gum Bacterium in 96% of Alzheimer’s Brains, walks through the research on a mouth bacterium found in brain tissue. Before going further, one plain statement: Measura [Cardiometabolic and Autonomic Health Analysis] does not examine gums, does not test saliva, and has no test for any bacterium. That work belongs to a dentist or periodontist. What Measura can do is measure the person those gums belong to: blood sugar control, blood vessel function, and cognition.

Is gum disease linked to dementia? The risk sits with severe disease

Groups of researchers working independently kept finding the same thing: people with periodontal disease develop dementia more often. An umbrella review pooling that work put the extra risk at roughly a quarter and graded the certainty low to moderate. The detail that matters most is the gradient. Severe periodontitis came with close to three times the odds of dementia, while disease milder than moderate showed no measurable excess at all.

So a little pink in the sink is a reason to book a dental visit. It is not a sign your memory is at risk. The exposure these studies point to is deep, bleeding, long-untreated infection, and it is common and quiet. A CDC analysis that examined every tooth in 10,683 American adults aged 30 to 79 found periodontitis in 42% and the severe form in 7.8%. Most people with it do not know.

Is the gum bacterium found in Alzheimer’s brains?

In 2019, a team looked for gingipains, the protein-cutting enzymes made by the gum bacterium Porphyromonas gingivalis, in brain samples. One of them turned up in 96% of Alzheimer’s samples, 51 of 53, and the amount tracked with markers of the disease. That is the headline. The same figure also shows the enzyme in 39% of samples from people without dementia, and the second gingipain in 52% of them. This organism is not a stranger to ordinary brains. What set Alzheimer’s tissue apart was how much was there.

Two more facts belong beside that result. Twelve of the paper’s twenty-five authors worked for the company developing a gingipain-blocking drug, and no lab without a stake in that drug has repeated the brain staining. And a separate experiment in 20 ordinary mice, 10 exposed and 10 not, showed that painting the bacterium on the gums for 22 weeks put it in the brain alongside inflammation, amyloid and tau. That shows the path can run from mouth to brain in an animal. It measured tissue, not memory, and it has not been repeated.

Does sugar feed the gum bacterium linked to Alzheimer’s?

A popular claim says this bacterium survives only if you eat carbohydrates. Dr. Padda corrects it, even though it comes from people arguing the same side he does. P. gingivalis cannot use sugar for energy. It feeds on protein and pulls iron from blood. The real chain is less tidy and more convincing: a sugary diet feeds other mouth bacteria, shifts the balance, and inflames the gums. Inflamed, bleeding pockets deliver exactly the blood proteins this organism eats, and they open a door into the bloodstream.

That door opens more often than people assume. Pooled studies found that toothbrushing puts bacteria into the blood in 8 to 26% of people, and plaque or gum inflammation roughly triples the odds. With healthy gums, that is trivial. With chronic periodontitis, it happens with an ordinary habit, day after day, for years. The gap is partly structural: teeth and the rest of the body are handled in separate offices, with separate charts, so the chronic wound in the mouth rarely appears in the medical record where cognition and blood sugar are tracked.

Does treating gum disease prevent dementia?

No one has shown that treating gum disease prevents dementia. The one large drug test, the GAIN trial, gave a gingipain blocker to 643 people with mild to moderate Alzheimer’s for 48 weeks and missed both main goals. Liver enzymes rose in 15% of the high-dose group against 2% on placebo, and the program was shut down in 2022. Among the 242 participants with the bacterium in their saliva, decline ran 57% slower on the higher dose, a subgroup result inside a failed trial, which is weak evidence. A follow-up trial will not report until 2029. Two genetic studies looking for a causal link found nothing that held up. And GAIN excluded people with poorly controlled diabetes or severe obesity, the metabolically complex patients most likely to be reading this.

What Measura can measure in the same person

The oral evidence cannot be collected at Measura. The body it happens in can be. A cognitive assessment sets a baseline for memory and thinking while you feel fine, so any later change has something to be compared against. Laboratory panels cover blood sugar control; in people with diabetes, a Cochrane review of 30 studies found that deep gum cleaning lowered HbA1c by about 0.43% at three to four months, so the dental chart and the A1C belong in the same conversation. And arterial stiffness and endothelial function testing looks at how stiff your arteries are and how their lining responds, the same territory a periodontal treatment trial tracked in people with severe gum disease. None of these tests detects gum disease. Together they show whether the chronic inflammation in your mouth is keeping company with trouble elsewhere.

Questions for two appointments

At the dentist: ask for a full-mouth periodontal examination rather than a quick screening, and for your periodontal inflamed surface area, a figure in square millimeters calculated from probing depths and bleeding. Partial exams can miss more than half of disease.
At your physician: ask for your A1C to be read next to that dental chart, and ask about your 25-hydroxyvitamin D, which your immune cells use to make one of the body’s own antimicrobial peptides. No source sets a target level for that purpose.
On timing: do not have an inflammation marker such as hs-CRP drawn the day after a deep cleaning, because it rises briefly afterward.

Treating the gums is worth doing on its own merits: you keep your teeth and lower a chronic inflammatory burden, whether or not the brain link is ever proven. Measurement tells you where you stand while that question waits. The complete evidence is in the book companion (the Chapter 8 companion page), and the earlier article in the series covers the sugar-driven inflammation behind this story (does sugar cause inflammation).

Frequently asked questions

Do bleeding gums mean I am going to get dementia?

No. The pooled studies tie dementia risk to severe periodontitis, and gum disease milder than moderate showed no measurable excess. Bleeding when you brush is a reason to see a dentist soon, because it is treatable and it lets bacteria into the bloodstream more often. If memory is a worry, a cognitive baseline answers a different question than a dental exam does. More in memory and cognitive screening.

Can Measura test me for P. gingivalis?

No. Measura has no microbial, saliva or dental test. Saliva testing for the bacterium was done as part of a research drug trial and is not a routine clinical test. Your dentist or periodontist assesses the gums. Measura measures the metabolic, vascular and cognitive picture in the same person, which is useful alongside a dental chart but is not a replacement for one. A full list is in what Measura actually measures.

Will treating my gum disease protect my memory?

That has not been shown. The only large drug trial aimed at this bacterium failed, and genetic studies found no causal link that held up. Treatment is still worthwhile: it saves teeth, removes a chronic source of inflammation, and in people with diabetes it lowered A1C in pooled trials. The connection between the mouth and blood sugar is covered in insulin resistance and metabolic health.

Why did I feel worse after a deep cleaning?

That is the documented course. In a randomized trial of 120 people with severe periodontitis, intensive treatment briefly worsened blood vessel function and raised inflammatory markers at 24 hours, then improved vessel function by six months. Feeling off the next day is expected and passes. It is also why blood inflammation markers should not be drawn right after treatment. Vascular measurement is described on the arterial stiffness and endothelial function page.

Why get a cognitive baseline if my memory is fine?

Because change is only visible against a starting point. A score taken while you feel well turns a vague later worry into a comparison with real numbers. That matters for anyone with risks that build silently for decades, including chronic inflammation from the mouth or elsewhere. A baseline does not predict dementia; it makes future testing interpretable. More in what a cognitive baseline is for.

Is there a link between brushing teeth and dementia?

Brushing itself is not the problem. Pooled studies found that toothbrushing puts mouth bacteria into the blood in 8 to 26% of people, and plaque or gum inflammation roughly triples those odds. With healthy gums that is trivial. With chronic periodontitis it happens day after day for years, which is why the severe gum disease tied to dementia is the one worth treating.

Can gum bacteria travel to the brain?

In animals, yes. Painting the gum bacterium on the gums of mice for 22 weeks put it in the brain alongside inflammation, amyloid and tau. In people, one of its enzymes turned up in 96% of Alzheimer’s brain samples, and also in 39% of samples from people without dementia. What set Alzheimer’s tissue apart was how much was there, not whether it was there at all.

Does sugar cause the gum disease linked to Alzheimer’s?

Indirectly. P. gingivalis cannot use sugar for energy; it feeds on protein and pulls iron from blood. A sugary diet feeds other mouth bacteria, shifts the balance and inflames the gums. Those inflamed, bleeding pockets then supply the blood proteins this organism eats and open a door into the bloodstream. The inflammation side of that chain is covered in does sugar cause inflammation.

Measure the body your gums belong to

Request Measura testing for a cognitive baseline, blood sugar markers and vascular function, with results sent to your physician to read alongside your dental care.

Send a message

4477 Woodson Rd, Suite 201, St. Louis, MO 63134. Monday to Friday, 9:00 a.m. to 5:00 p.m. Please do not send symptoms, diagnoses or images through a web form — a website form is not a secure medical channel. Send your name and number and we will call you back.

References

Qadir, B. H., Mahmood, M. K., Amin, Y. M. M., Kurda, H. A., Rasheed, T. A., Noori, A. H., Noori, Z. F., Abdulghafor, M. A., Fadhil, H. N. M., Fatih, M. T., Tardivo, D., Tassery, H., & Lan, R. (2025). Periodontitis and tooth loss are associated with higher risks of cognitive disorders: A systematic umbrella meta-analysis. Clinical and Experimental Dental Research, 11(6), Article e70240. https://doi.org/10.1002/cre2.70240
Kim, D.-H., & Han, G.-S. (2025). Periodontitis as a risk factor for dementia: A systematic review and meta-analysis. The Journal of Evidence-Based Dental Practice, 25(2), Article 102094. https://doi.org/10.1016/j.jebdp.2025.102094
Eke, P. I., Thornton-Evans, G. O., Wei, L., Borgnakke, W. S., Dye, B. A., & Genco, R. J. (2018). Periodontitis in US adults: National Health and Nutrition Examination Survey 2009–2014. Journal of the American Dental Association, 149(7), 576–588.e6. https://doi.org/10.1016/j.adaj.2018.04.023
Dominy, S. S., Lynch, C., Ermini, F., Benedyk, M., Marczyk, A., Konradi, A., Nguyen, M., Haditsch, U., Raha, D., Griffin, C., Holsinger, L. J., Arastu-Kapur, S., Kaba, S., Lee, A., Ryder, M. I., Potempa, B., Mydel, P., Hellvard, A., Adamowicz, K., … Potempa, J. (2019). Porphyromonas gingivalis in Alzheimer’s disease brains: Evidence for disease causation and treatment with small-molecule inhibitors. Science Advances, 5(1), Article eaau3333. https://doi.org/10.1126/sciadv.aau3333
Ilievski, V., Zuchowska, P. K., Green, S. J., Toth, P. T., Ragozzino, M. E., Le, K., Aljewari, H. W., O’Brien-Simpson, N. M., Reynolds, E. C., & Watanabe, K. (2018). Chronic oral application of a periodontal pathogen results in brain inflammation, neurodegeneration and amyloid beta production in wild type mice. PLoS ONE, 13(10), Article e0204941. https://doi.org/10.1371/journal.pone.0204941
Martins, C. C., Lockhart, P. B., Firmino, R. T., Kilmartin, C., Cahill, T. J., Dayer, M., Occhi-Alexandre, I. G. P., Lai, H., Ge, L., & Thornhill, M. H. (2023). Bacteremia following different oral procedures: Systematic review and meta-analysis. Oral Diseases, 30(3), 846–854. https://doi.org/10.1111/odi.14531
Tomás, I., Diz, P., Tobías, A., Scully, C., & Donos, N. (2011). Periodontal health status and bacteraemia from daily oral activities: Systematic review/meta-analysis. Journal of Clinical Periodontology, 39(3), 213–228. https://doi.org/10.1111/j.1600-051X.2011.01784.x
Simpson, T. C., Clarkson, J. E., Worthington, H. V., MacDonald, L., Weldon, J. C., Needleman, I., Iheozor-Ejiofor, Z., Wild, S. H., Qureshi, A., Walker, A., Patel, V. A., Boyers, D., & Twigg, J. (2022). Treatment of periodontitis for glycaemic control in people with diabetes mellitus. Cochrane Database of Systematic Reviews, 4(4), Article CD004714. https://doi.org/10.1002/14651858.CD004714.pub4
Tonetti, M. S., D’Aiuto, F., Nibali, L., Donald, A., Storry, C., Parkar, M., Suvan, J., Hingorani, A. D., Vallance, P., & Deanfield, J. (2007). Treatment of periodontitis and endothelial function. New England Journal of Medicine, 356(9), 911–920. https://doi.org/10.1056/NEJMoa063186
Nesse, W., Abbas, F., van der Ploeg, I., Spijkervet, F. K. L., Dijkstra, P. U., & Vissink, A. (2008). Periodontal inflamed surface area: Quantifying inflammatory burden. Journal of Clinical Periodontology, 35(8), 668–673. https://doi.org/10.1111/j.1600-051X.2008.01249.x