Q&A: Dr. Jonathan Levine on what your mouth has to do with your brain health

Dr. Jonathan B. Levine is a dentist, oral health researcher, professor, and founder of Smile House. His work sits at the intersection of oral care and systemic health.

In this Q&A, Dr. Levine explains what’s actually connecting your gums to your brain, and why your dental routine might be one of the most overlooked tools in long-term brain health.

A study of over 30 million adults found more than a twofold increase in Alzheimer’s risk among people with poor oral health. What’s the most important thing readers should understand before jumping to conclusions?

JL: The most important fact is that this research shows a direct association between chronic inflammation in the mouth and Alzheimer’s disease. We know that Alzheimer’s is driven by a constellation of risk factors—it’s not one single cause—and chronic oral inflammation is now understood as one of those factors.

Here’s the biological pathway: during chronic gum inflammation and bleeding, what we call “leaky gums,” oral bacteria such as Porphyromonas gingivalis and its toxic enzymes, called gingipains, can enter the bloodstream. Over time, these bacterial components can cross the blood-brain barrier—particularly when our immune response is weakened by age or ongoing inflammation.

The encouraging part is that periodontal disease is a modifiable risk factor. That means by focusing on excellent oral health and controlling harmful bacteria, we may be able to reduce systemic inflammation and provide a real neuroprotective benefit.

You used the phrase “leaky gums.” That’s not something most people have heard before. Can you explain what that actually means and why it matters beyond your mouth?

JL: When your gums are chronically inflamed and bleeding—even if it’s mild enough that you might brush it off—it creates an opening. Harmful bacteria and the inflammatory molecules they produce can enter your bloodstream through that compromised tissue.

This is significant because it means oral health isn’t just an oral issue. Today, there are 57 diseases linked to chronic inflammation in the mouth, including cardiovascular disease, diabetes, and cognitive decline.

Why might tooth loss specifically be a more meaningful signal than cavities or gum disease on their own?

JL: Tooth loss reflects something more serious than a single cavity or the early stages of gum disease. It’s typically the result of chronic, unresolved problems — advanced periodontal disease, severe decay, or physical trauma that went untreated.

Losing teeth signals a significant disruption of the oral microbiome and long-standing underlying inflammation. It’s a sign that something has been going on for a while, and it warrants evaluation and intervention by a dental professional.

Researchers point to inflammation and the oral microbiome as key links to brain health. What’s the most plausible mechanism here?

JL: Research suggests that oral inflammation and microbial imbalance—what’s called dysbiosis—can influence brain health through pathways similar to the gut-brain axis. The mouth, gut, and brain are part of a complex, bidirectional communication network. When that system is out of balance, it sends signals that affect brain function.

Harmful oral bacteria and the inflammatory molecules they produce can enter the bloodstream or travel via nerves, potentially contributing to cognitive decline over time. Maintaining a balanced oral microbiome and controlling inflammation are important not just for your teeth, but for long-term brain health.

You’ve said 70% of American adults have some form of gum disease. What are the warning signs most people overlook or dismiss?

JL: Bleeding when you brush or floss is the most common one. Many people assume it’s normal. It’s not. Bleeding gums are a sign of inflammation, and that inflammation is exactly what we’ve been talking about.

Other signs include persistent bad breath, gums that look red or swollen, gums that are receding or pulling away from your teeth, and teeth that feel loose. Any of these should prompt a conversation with your dentist. The earlier you catch gum disease, the more you can do about it.

If oral health truly plays a role in long-term brain health, what are the preventive actions that matter most?

JL: Midlife is a critical window to assess and manage oral inflammation before symptoms of cognitive decline appear. The basics matter most: brushing twice a day for a full two minutes, flossing daily, and scheduling regular professional cleanings.

These habits prevent the buildup of the same harmful bacteria associated with Alzheimer’s, diabetes, and cardiovascular disease. Beyond that, pay attention to nutrition, stress management, and sleep quality. All of these support oral balance and, increasingly, brain health. 70% of American adults have some form of gum disease. We can’t start early enough.

Dr. Levine’s work reinforces something most people don’t consider: oral health isn’t isolated from the rest of your body. The same inflammation that damages your gums may be contributing to far more serious conditions, and the preventive actions are ones most of us already know how to do.