Can Flossing Lower Your Stroke Risk?
Clinically reviewed by Dr. Abinaash Kaur, DDS, RCDSO, on 2026-08-21. Dr. Kaur is a general dentist in Toronto (Bloor West Village) registered with the Royal College of Dental Surgeons of Ontario.
Possibly, and nobody has proved it. Two large studies published in 2026 found that people who clean between their teeth had about 23% fewer ischemic strokes, the clot kind (Journal of Dentistry via PubMed, Stroke via PubMed).
Both are observational studies. They can show that two things travel together. They can't show that one causes the other.
I've practised in Bloor West Village for about 25 years, and this headline reached the chair faster than most. People are reading it on their phones in the waiting room and asking me before they've sat down.
Here's the part that keeps getting dropped. The number everyone is quoting isn't measuring the thing everyone thinks it's measuring.
Whether flossing is worth doing at all is a separate argument, and I've been through that one in Floss or Toss?. The stroke claim is narrower, and it's the one I'm answering here.
What did the two studies actually find?
Two research groups, two countries, two different sets of people. Both landed on the same number.
The first followed 98,866 Korean adults aged 40 and over who had a health exam and a dental exam in 2009 and 2010, then tracked their stroke hospitalizations from 2011 through 2019 (Journal of Dentistry via PubMed). People who brushed at least twice a day and regularly used both floss and interdental brushes had a 23% lower risk of ischemic stroke (Journal of Dentistry via PubMed).
The second comes from a long-running American heart study. 6,200 adults with their own teeth answered a flossing questionnaire in the late 1990s, and researchers followed them for a median of 23.7 years (Stroke via PubMed).
Over that stretch, 434 ischemic strokes happened (Stroke via PubMed).
Flossing carried an adjusted hazard ratio of 0.77 for ischemic stroke, 0.60 for the clot-from-the-heart type, and 0.88 for atrial fibrillation, the irregular heartbeat behind that type (Stroke via PubMed). A hazard ratio of 0.77 is the same 23% lower risk the Korean study reported.
In plain counts, 8.7% of nonflossers had an ischemic stroke against 6.1% of flossers (Stroke via PubMed).
Most people think a study tested floss. What did it test?
The Korean study never isolated flossing.
Its exposure was a bundle: brushing at least twice a day, plus floss, plus interdental brushes, all together, measured against people doing less of all three (Journal of Dentistry via PubMed). The authors' own conclusion names all three practices in the same breath (Journal of Dentistry via PubMed).
So "flossing cuts stroke risk by 23%" isn't what that paper reports. It reports that people with the full between-teeth routine had fewer ischemic strokes than people without one (Journal of Dentistry via PubMed).
The American study is the one that pulled flossing out on its own, adjusting for regular brushing, dental visits, gum disease and cavities (Stroke via PubMed). It landed on the same figure.
Two studies measuring two different things and arriving at one number reads like double confirmation. It's closer to a coincidence worth noticing.
Could it just be that flossers are healthier people?
That's the first question I had, and the American researchers had it too.
They put it in the paper. Before the study even began, flossers had significantly lower rates of vascular risk factors, gum disease and tooth decay than nonflossers (Stroke via PubMed).
People who floss tend to do other things as well. They show up for dental visits. They're less likely to smoke. They're often the same people who take the blood pressure pill every morning.
Researchers have a tool for exactly this worry. It's called an E-value, and it asks how strong a hidden factor would have to be to wipe out the finding. Here it came to 1.87 (Stroke via PubMed).
Plain version: something nobody measured would need to be nearly twice as tied to both flossing and stroke as everything already counted. That isn't impossible. It isn't trivial either.
The same team checked two inflammation markers in the blood. One showed no difference between the groups, and the apparent difference in the other disappeared once age, body weight and smoking were accounted for (Stroke via PubMed).
Has anyone proved that cleaning between your teeth prevents a stroke?
No, and the hole in the evidence is bigger than most people would guess.
Cochrane reviewers track the trials on treating gum disease to prevent heart attacks and strokes. Their 2022 update found no new completed randomized trials since 2019 (Cochrane Database of Systematic Reviews via PubMed).
Two trials existed at all. Both were rated at high risk of bias, and the evidence was graded very low certainty (Cochrane Database of Systematic Reviews via PubMed).
On preventing a second cardiovascular event in people who already have heart disease, the reviewers wrote that they were unable to draw any conclusions (Cochrane Database of Systematic Reviews via PubMed).
That's the ceiling on this whole topic. The association is well documented. The cause is not settled.
Why would your gums have anything to do with your brain?
The idea isn't far-fetched, which is why researchers keep chasing it.
Gum disease starts with plaque, an invisible bacterial film that forms on your teeth every day (Canadian Dental Association). Inflamed gums are a raw, bleeding surface sitting directly on a blood supply, which makes them a door into the bloodstream.
That door opens more often than people realize. In a randomized study in Circulation, 290 people either brushed their teeth or had a tooth taken out, with blood drawn six times. Bacteria of the kind that can infect a heart valve turned up in 23% of the toothbrushing group (Circulation via PubMed).
The population numbers point the same way. A 2025 review pooling 36 studies and more than 7.6 million people found higher odds of stroke in people with gum disease, at 1.72 (Journal of Evidence-Based Dental Practice via PubMed).
The odds ran higher for advanced gum disease (periodontitis) than for early gum inflammation (gingivitis), 2.01 against 1.67, and higher for clot strokes than for bleeding strokes, 1.85 against 1.48 (Journal of Evidence-Based Dental Practice via PubMed).
Treatment moves something measurable, too. In a New England Journal of Medicine trial, 120 people with severe gum disease got either intensive gum treatment or ordinary care, and the researchers tracked how well the arteries widened when blood flow increased (New England Journal of Medicine via PubMed).
For the first 24 hours after treatment, that measure got worse. By 60 days it was better than the control group, and by 180 days better still (New England Journal of Medicine via PubMed).
Arteries widening better is not the same as strokes not happening. Nobody has shown that better arteries at six months turn into fewer strokes.
What actually moves stroke risk the most?
Blood pressure, by a distance.
The Public Health Agency of Canada names high blood pressure as the most important modifiable risk factor for stroke (Public Health Agency of Canada). The rest of its list is a healthy weight, a healthy diet, regular exercise, not smoking, not drinking excessively, and to some extent controlling cholesterol (Public Health Agency of Canada).
Floss doesn't appear on it.
Stroke is the third leading cause of death in Canada, and the number of survivors climbed from 526,200 in 2003-2004 to 741,800 in 2012-2013 (Public Health Agency of Canada). Those are the stakes the headline is borrowing.
My read: clean between your teeth because it protects your teeth and gums, which is the settled part. Treat any stroke benefit as a possible bonus that hasn't been shown, and keep the blood pressure appointment.
So what should you do tonight?
Clean between your teeth once a day, with whatever tool you'll keep picking up.
The Canadian Dental Association frames it as surface area. Skip flossing and you're missing more than one third of your tooth surface (Canadian Dental Association). Plaque hardens into tartar within 24 to 36 hours, and once it's hard only a professional cleaning takes it off (Canadian Dental Association).
String floss isn't the only tool, and it may not be the strongest one.
Cochrane's review of 35 trials and 3,929 adults found that adding floss to brushing may reduce gum inflammation, on low-certainty evidence, and that interdental brushes may do it better than floss (Cochrane Database of Systematic Reviews via PubMed). The same reviewers noted the effect sizes they saw may not be clinically important (Cochrane Database of Systematic Reviews via PubMed).
Notice which two tools the Korean study asked about. Floss and interdental brushes, both of them (Journal of Dentistry via PubMed).
If string floss is a nightly fight, our comparison of water flossers and string floss walks through the trade-offs, and toothbrushes 101 covers the brushing half of the job.
Have no fear about a little blood at first. Gums often bleed when you start flossing, and it usually stops after a few days (Canadian Dental Association). If it keeps going, that's worth a look, and our post on bleeding gums explains what we check for.
Are Canadian gums getting better or worse?
Worse, on the only direct measurements we have.
Statistics Canada released measured oral health data in December 2025, the first such measurements in more than 15 years (Statistics Canada). Among adults aged 20 to 79, 83% had gums that bled somewhere during probing, seven teeth on average (Statistics Canada).
The pockets between gum and tooth deepened as well. Just over a third of adults now measure 4 mm or more, against one in five in 2007-2009 (Statistics Canada).
The worst bleeding rates showed up in the youngest adults, at 90% of people aged 20 to 39, against 76% of those aged 60 to 79 (Statistics Canada).
Did you know about this? Most people picture gum disease arriving with grey hair.
For the wider picture of how the mouth ties into the rest of the body, our post on the mouth as the front door and the one on gum health and your heart go further. If your gums bleed and you're confident it isn't your brushing, our post on the other causes covers them.
How often you need a professional cleaning is an individual call, and our post on cleaning intervals goes through what changes it.
Frequently Asked Questions
Q: Can flossing lower your stroke risk? It's linked to a lower rate, which isn't the same as lowering it. Two 2026 cohort studies found roughly 23% fewer ischemic strokes among people who clean between their teeth (Journal of Dentistry via PubMed, Stroke via PubMed). Neither study assigned anyone to floss, so neither can show cause.
Q: How big was the effect in the studies? In the Korean cohort of 98,866 adults, brushing twice daily plus floss plus interdental brushes carried a 23% lower risk of ischemic stroke (Journal of Dentistry via PubMed). In the American cohort of 6,200 adults, 8.7% of nonflossers had an ischemic stroke against 6.1% of flossers over a median 23.7 years (Stroke via PubMed).
Q: Is there a trial proving gum care prevents strokes? No. The 2022 Cochrane update found no new completed randomized trials since 2019, and rated the two existing trials at high risk of bias with very low certainty evidence (Cochrane Database of Systematic Reviews via PubMed). For people who already have heart disease, the reviewers said they were unable to draw conclusions (Cochrane Database of Systematic Reviews via PubMed).
Q: Is an interdental brush better than floss? It may be, for gum inflammation. A Cochrane review of 35 trials in 3,929 adults reported that interdental brushes may reduce gum inflammation more than floss, on low-certainty evidence, and that the effect sizes seen may not be clinically important (Cochrane Database of Systematic Reviews via PubMed). The tool you'll use every day beats the tool that stays in the drawer.
Q: My gums bleed when I floss. Should I stop? No. Gums commonly bleed when you first start flossing, and the bleeding usually stops within a few days (Canadian Dental Association). Bleeding that carries on is worth having looked at, and it's common company: 83% of Canadian adults aged 20 to 79 show gum bleeding on probing (Statistics Canada).
Q: How does gum bacteria reach the bloodstream at all? Through the gums, during ordinary daily activity. A randomized study of 290 people found bacteria of the kind that can infect a heart valve in the bloodstream of 23% of those who brushed their teeth (Circulation via PubMed). Healthier gums mean a smaller doorway.
Q: I have high blood pressure. Should I focus on that or on flossing? Both, with blood pressure first. The Public Health Agency of Canada names high blood pressure as the most important modifiable risk factor for stroke, alongside weight, diet, exercise, smoking, alcohol and cholesterol (Public Health Agency of Canada). Cleaning between your teeth is worth doing on its own merits, and the two minutes it takes don't compete with anything.
Reviewed by Dr. Abinaash Kaur, B.Sc., DDS (University of Toronto Faculty of Dentistry), who has practised general and family dentistry in Bloor West Village for about 25 years. This article is general oral health information, not a diagnosis or a substitute for an examination.
Not sure whether your gums are healthy or quietly inflamed? Come in and we'll measure them, show you the numbers, and set up a between-teeth routine you'll keep. We're at 750 Annette Street in Bloor West Village, serving the Junction, High Park, and Baby Point. Book a visit with The Village Dentist and we'll take a proper look.
