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Regular brushing and flossing are vital to the health of your teeth and gums. We all know that—it's been drummed into our heads since we first picked up a toothbrush.

But brushing your teeth might not just be good for your oral health: It could help protect your brain, too. Because according to studies over the last few decades, there seems to be a connection between brushing your teeth and, of all things, Alzheimer's disease. This connection centers around an oral infection called periodontitis.

It's a condition that destroys soft tissue in the gums and eats away at the bone that supports the teeth. Left to its own devices, it will give bacteria a breeding ground, wreck someone's pearly whites, and leave them with bleeding gums. So, it's not a great time.

There are a whole lot of things that can increase someone's risk of developing this, including a lack of teeth-brushing and factors like smoking and metabolic diseases. But thankfully, preventing it is often super straightforward:. Just keep good oral hygiene habits, and see a dentist regularly.

Of course, that's often easier said than done. So periodontitis is pretty common, with the Centers for Disease Control and Prevention in the United States citing that about 50% of people thirty or over have it to some degree. From just a dental hygiene perspective, that's not good news.

But some researchers also believe there's another consequence of this condition: that a bacterium associated with it, called P. gingivalis, seems to be capable of contributing to Alzheimer's symptoms. If you know a bit about Alzheimer's, you might be thinking, “This could make some sense!” Because a common explanation for the disease's symptoms is that they're at least partly caused by plaques in the brain made of the compound amyloid beta. That plaque hypothesis is still out there—although it's repeatedly failed to stand up to scrutiny.

But regardless, this idea doesn't call amyloid beta into question. Instead, the two hypotheses fit together quite nicely. The idea is that, as periodontitis breaks down cells in the gums, P. gingivalis is able to break into the rest of the body.

From there, it can travel to more distant organs and establish bacterial colonies in places it's not meant to be. Including, as animal studies have confirmed, the brain. There, P. gingivalis releases toxins called gingipains, and that's when things start to get really messy.

The thinking is that these toxins compromise the tissue structure around the bacterial colonies. That makes the brain's protective barrier leaky, damages cells, and impacts cells' ability to function correctly. So, in response to that, compounds that are associated with the damage, like amyloid beta, could form and act like a scab over these wounds.

There's even evidence that suggests P. gingivalis could make it harder for the brain to get rid of this stuff. One 2017 study from the Journal of Alzheimer's Disease showed that the presence of this bacteria in the brain could alter sleep cycles by messing with how certain brain cells respond to light and set our bodies' clocks. And considering how the brain cleans itself of toxins as we sleep, that kind of damage could have a direct effect on how the body could clean out both P. gingivalis and molecules like amyloid beta.

That's a lot of consequences for one measly gum bacterium. Now, it is worth taking a second to say that Alzheimer's is a complicated disease with multiple factors. So even if someone has dental trouble, that doesn't mean their fate is sealed.

But since there does seem to be a connection here, it's something people have been looking into. They've been studying this relationship and even trying to figure out if P. gingivalis could be used as a biomarker— in other words, if you could test for it as a sign that someone might be at risk of developing Alzheimer's. And of course, they've also been trying to figure out how to tackle this bacterium head-on.

With some promising results, I might add. In a 2019 study, researchers infected mice with this bacterium, and, as expected, saw it colonize the mice's brains. They also saw an Alzheimer's-like increase in amyloid beta plaques.

But, by injecting a small molecule that blocked P. gingivalis's ability to get energy, the team was able to reduce both the number of bacteria and the associated inflammation. This stopped the production of amyloid beta, and as the paper put it, “rescued” neurons in the hippocampus, a brain area vital for memory. Of course, this study was only in mice, but more information may be just around the corner, because that small molecule is now being tested in humans, too.

Two Phase I clinical trials testing the safety of the drug were completed in 2018, and when we filmed this video in 2020, a Phase 2 trial to further examine safety and efficacy was underway. That's a good starting point. But while we wait for results, maintaining good oral hygiene to avoid periodontitis seems to be a great way to reduce risk, too.

Alzheimer's is a slippery character. Historically-speaking, scientists have had a hard time finding causes and treatments for it, and this P. gingivalis thing is just one hypothesis among many. Even so, these findings seem to provide a promising new target for Alzheimer's prevention, and hopefully, we'll see some fully-fledged treatments as a result.

Because when it comes to a disease like this… well, having multiple treatment options isn't a bad thing. This episode of SciShow Psych was made possible because of our patrons on Patreon— people who allow us to keep diving into the latest research and making videos like this. So if you're a patron, thank you so much!

If you'd like to consider joining our Patreon community, you can go to patreon.com/scishow. And in any case, thanks for watching this episode. We're glad to have you. [OUTRO ♪].