Live Long and Well with Dr. Bobby
Let's explore how you can Live Long and Well with six evidence based pillars: exercise, good sleep, proper nutrition, mind-body activities, exposure to heat/cold, and social relationships. I am a physician scientist, Ironman Triathlete, and have a passion for helping others achieve their best self.
Live Long and Well with Dr. Bobby
Can flossing reduce your risk of a stroke?
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Can a simple habit like flossing really reduce your risk of stroke? In this episode, Dr. Bobby unpacks the headlines sparked by a recent presentation at the American Stroke Association’s International Conference that claimed regular flossing could reduce stroke risk by 20–50%.
Dr. Bobby begins with a refresher on the importance of stroke prevention. From there, he explores the biological plausibility of a connection between oral health and cardiovascular events. While Americans are fairly diligent about brushing (with 90% brushing once daily and 60% brushing twice a day per YouGov data), flossing habits lag significantly (NIH Oral Health Study—highlighting a clear opportunity if the flossing-stroke link is real.
Dr. Bobby dives into the study behind the headlines, a new analysis from the long-running Atherosclerosis Risk in Communities (ARIC) study, which tracked over 6,000 individuals for 25 years. The preliminary finding: regular flossers had significantly lower risk of ischemic and cardioembolic strokes (Study Abstract). Surprisingly, brushing and dental visits showed no significant benefit in this analysis.
So why isn’t this flossing-stroke connection headline a "five-alarm fire" in medicine? Dr. Bobby explains the limitations: the results were shared via a conference abstract, not a peer-reviewed journal article. Without full access to the data or understanding how many other hypotheses were tested from this large dataset (which has already generated over 2,300 publications), we risk falling into the trap of correlation being mistaken for causation.
To further evaluate the credibility of this association, Dr. Bobby introduces the Bradford Hill criteria—nine principles to assess causality in observational studies. While the biological plausibility is strong and the effect size notable, the study fails on criteria like replication, dose-response, and publication rigor (Bradford Hill Overview).
In closing, Dr. Bobby affirms the benefits of flossing—not necessarily for stroke prevention, but for better oral health, which is valuable in its own right. He shares his personal oral care routine, including flossing nightly and using a water jet, while reminding listeners to stay evidence-informed in their health decisions.
Takeaways
Flossing likely improves oral health, but its role in stroke prevention remains unproven.
Be cautious with headlines drawn from unpublished conference abstracts—they’re a starting point for inquiry, not a reason to change behavior just yet.
"How to Live Long and Well" at DrBobbyLiveLongAndWell.com.
Can flossing your teeth really reduce your risk of stroke? Recent headlines suggest that it may be true, but does the evidence support this? Is it even biologically plausible? Let's explore what we know and, most importantly, what we don't know. Hi, I'm Dr Bobby Du Bois and welcome to Live Long and Well, a podcast where we will talk about what you can do to live as long as possible and with as much energy and figure that you wish. Together, we will explore what practical and evidence-supported steps you can take. Come join me on this very important journey and I hope that you feel empowered along the way. I'm a physician, ironman, triathlete and have published several hundred scientific studies. I'm honored to be your guide. Welcome, my wonderful listeners to episode 35.
Speaker 1:Can flossing reduce your risk of stroke? Well, it's a fascinating question and we, of course, don't want to get a stroke. And there was a recent study and lots of headlines in all the news media that said flossing reduces our risk of stroke by 20 to 50 percent, depending upon the type of stroke. Now, this was based on a presentation at the American Stroke Association's International Conference on Stroke and it was widely picked up by the media, by the New York Post, the San Francisco Chronicle, youtube post, the San Francisco Chronicle, youtube Times, uk Jerusalem post, and we are going to dive into this study shortly. But why discuss this topic? Well, the headline is really catching Flossing reduces our risk of a stroke. Now the question, of course, is is there anything to this and beyond just this study? Are there lessons to glean from all the headlines? All the attention? Are those lessons things that can teach us how to approach future headlines and whether to believe it or not? Now, as you may recall, in episode 22, health headlines helpful, harmful or just plain confusing we explored a headline that was worrisome, that intermittent fasting caused heart attacks, and now we did a bit of myth busting there and we showed a lot of the problems with that study. Is it the same scenario here, where this hype exceeds what the evidence tells us? Well, stay tuned, and we're going to figure this out.
Speaker 1:As I was thinking about explaining to you, my listeners, why are we doing an episode like this, I realized I was destined. It was my destiny to do this episode Now. I didn't know it 30 years ago, when I was visiting my dentist and at the time she had just come back from a conference in Hawaii. So this is in the 1990s or so and at that conference, basically, she learned how oral health, mouth issues, could cause heart disease. And I'm an internist, I'm a physician, she's a dentist and she's telling me about heart disease and she was saying, oh, we must brush our teeth and floss our teeth and that will potentially help the risk of heart disease. And she was very excited about this and told all of her patients my wife and my kids and everybody else. It turns out she may have been ahead of the medical community Back 30 years ago. This was not something that was commonly discussed. Well, we'll come back to this as well.
Speaker 1:Before we dive into the content, I have a request. This is episode 35, so I've been doing a whole bunch of these and I would love to get feedback from you about how I'm doing the topics you like, the topics you want more of, and there's a brief, brief questionnaire. It'll take you like two minutes and the link is in the show notes. So please, if you can do, take a couple of minutes and give me that feedback. Some of the questions I really want to learn from you do you like episodes that summarize evidence on a topic Like is there evidence that sleep is important or that nutrition matters. Do you like myth-busting? In some cases maybe today's episode is myth-busting Certainly the one on seed oils fits into that Do you like that type? How about the ones where I share a personal health journey, like the one I did recently on my needing a brain MRI and what happened? Also, the framework episodes Do you Like your Doctor? Where I sort of lay out how to think through things. So I'd love to get your input on that, on any new topics you might suggest and, most importantly, how long my episode should be. I've aimed for 30 minutes. Should they be 20 minutes? Should they go 40 minutes? Are you okay if they go longer? I have tried to avoid many of the other health podcasts length of an hour hour and a half two hours, all right.
Speaker 1:Well, let's dive into our study for today and our topic today Can flossing reduce our risk of a stroke? Now some stroke facts, because stroke is not something we talk about all the time. Heart attacks we talk, not something we talk about all the time. Heart attacks we talk about, we hear about all the time. Stroke for a while hasn't been really front and center Yet. There's about 800,000 strokes that happen in the US every year, and about every 40 seconds there's a stroke, and about every three minutes somebody dies of a stroke. Equally importantly, stroke causes major disability. You might not be able to move on one side or a part of your body, you might not be able to speak. Well, all sorts of disabilities can come out of it. So it's a really, really important topic and could something as simple, really as simple, as flossing help us? Well, we need to talk a little bit about your mouth, oral health and how this possible solution or reduction in risk could occur.
Speaker 1:Well, we have, at any one point in time, about a billion bacteria in our mouths, just on our gums, on our teeth, in the saliva, and it is known quite clearly that if you brush or you're chewing, bacteria can and do get into our bloodstream. That, of course, doesn't sound very good. Well, if bacteria get in our bloodstream, they could cause direct damage, meaning those bacteria could go to other parts of our body and that could create problems for us. Or and I think this is perhaps more likely that the bacteria in our mouth that get in our bloodstream cause what I would call indirect damage, and that indirect damage is that it creates an inflammation, an inflammatory reaction and inflammation has been associated with heart attacks, cancer, metabolic disorders and the like. So this issue of the damage from the bacteria is really a sensual question. What we also know is that if your gums that surround and hold in your teeth, if they are inflamed, if they are infected, more bacteria are around and more bacteria can get into our body and cause problems. We also know good studies on this that if you brush and floss, it can reduce it does reduce your risk of gum disease. So theoretically now we're building an argument that the bacteria in our mouth could get in our bloodstream, could cause inflammation, and brushing and flossing has been shown to reduce that risk of inflammation in blood bacteria. Now we haven't made the leap yet to stroke or heart disease, but at least we're beginning to build a story and we have a lot of room for improvement in oral health.
Speaker 1:Studies show that Americans do brush pretty regularly, but they don't floss very regularly. Here's some data. So in a study that was published, 90% of us do brush at least once a day and 60% of us brush more than once a day. I'm a twice a day brusher myself, religiously, in the morning and at night. Now flossing we're not so good as Americans about flossing. A third of us don't floss at all. A third of us floss basically about once a week and only a third of us floss on a daily basis. Well, I'm a nightly flosser and I find that it makes a huge difference that even though I've brushed and gargled with mouthwash, there's still a lot of junk on my teeth. I've also found this is a simple hack that if you floss in front of a mirror close up, like makeup mirror boy, you make a lot better job of it than if you just floss in general, not looking at a mirror or even looking at your bathroom mirror. So if flossing were to matter and really if the study were true, gosh, there's a tremendous opportunity here, because a lot of us don't floss or don't floss really well.
Speaker 1:Okay, let's examine some more of the evidence connecting oral health with heart disease. Is it that a poor mouth, with gingivitis and other things, that it causes a heart disease or stroke, or is it just common factors? So perhaps the mouth doesn't cause stroke and heart disease. Perhaps it's things that hurt the mouth also hurt other parts of your body. So here's a perfect example Smoking. Smoking, we know, raises your risk of a heart disease or stroke. Smoking also worsens your oral health, so it may not be that the mouth is causing the problem. It just may be there's a common underlying factor like smoking or diabetes or getting older. Or, as the article might suggest to us, it is the presence of the problem in our mouth, your bacteria and gum disease, that causes heart disease or stroke.
Speaker 1:Now, as we've talked about many times, correlation doesn't mean causation. Just because we see that people with strokes have mouth disease or people with heart attacks have mouth disease doesn't mean one causes the other. Well, the American Heart Association reviewed the evidence and this is how they saw it. They said well, there's a lot of observational studies that support the relationship between mouth health and heart health, but they summarize that those observational studies don't say it's causative. It just means that they are potentially connected. Unfortunately, there haven't been any randomized controlled trials where some people get good oral care, some people don't. We follow them for 20, 30 years and we see who gets heart disease or strokes. Unfortunately, that study has never been done. I don't know if it ever will be done.
Speaker 1:Well, if the mouth and the heart, mouth and the stroke are causative, that the problems in one area create problems in the other. The theory is that it's due to, as I mentioned earlier, inflammation. Now we do have pretty good data that inflammation is associated with heart disease. One of the blood things that your doctor may order for you is called a CRP or C-reactive protein, or high-sensitivity CRP, and it's been shown many times that if that blood level which reflects inflammation is elevated, there's a much higher likelihood of having heart disease later on. And there's reasonable data that said, if you improve your oral health, it lowers those inflammatory markers. So we're starting to build a case that oral health relates to inflammation, the case that oral health relates to inflammation. We believe inflammation relates to heart disease and the like. But again, this is all just building a theoretical argument.
Speaker 1:All right, before we get to flossing, there is some data on toothbrush, brushing your teeth and heart disease. And if you brush just once a day or less than once a day, you have twice the risk of heart disease than if you brush two or more times a day. Again, all this evidence is observational. We don't have the randomized controlled trial, so we can't officially say there's a cause and effect relationship, but it is intriguing and maybe someday there will be that randomized trial. Okay, now we are ready to go on to the flossing study and to see whether the headlines are true or likely true and if not, what does it teach us about reading headlines carefully and understanding whether to believe it or not? Well, the title of the study was regular dental flossing may lower risk of stroke from blood clots and irregular heartbeats.
Speaker 1:This was a study, as I mentioned, that had been presented at a conference and it was from what was called the ERIC study atherosclerosis risk in communities. This is a large study that's been tracking over 6,000 people over 25 years, and the purpose of this big study was to see things that might relate to heart disease, so things like they might have measured 25 years at the beginning of the study, whether you smoke, whether you exercise, all sorts of different things and some of the things they asked related to oral health, and what they found was about two-thirds of people in this long-term study again, not a randomized trial, just an observational study about two-thirds of those folks did, in fact, floss, and those who flossed when they followed them over time had a 20% to 50% lower risk of a stroke Incredible. Now, it varied by type of stroke. That flossing didn't reduce your risk of all types of strokes, but important, important ones. Interestingly, they didn't find benefit for brushing and they didn't find benefit for visiting your dentist. So this is the first inkling that maybe this study isn't as valid as the headlines would suggest. But if it's true and there is that large reduction in stroke simply by flossing, maybe there could be as many as 50 to 150,000 fewer strokes in the United States each year. That is extraordinary. And why is this not what the firemen call a five-alarm fire? Now, when there are fires, there's alerts that go out and a five-alarm fire means the fire is out of control. Bring every resource you have, let's fight this fire. So why isn't this study and flossing a five alarm fire where everybody should be talking about it? Well, I have concerns with this study, not surprisingly. That's why I'm doing this episode. Surprisingly, that's why I'm doing this episode.
Speaker 1:Like our episode on health headlines and intermittent fasting causing death from heart disease, this set of headlines and study has some of the same problems. This was not a peer-reviewed published article. It was merely an abstract that was presented at a conference. So somebody wrote up a paragraph or two about the study and presented it at a meeting, and maybe there were a few different questions, but nobody has seen the full data, how the study was done, sent it out to other experts and ultimately undergo peer review and then publication in a peer-reviewed journal. None of this happened.
Speaker 1:I also mentioned that flossing seemed to help, but brushing and going to the dentist two other things that we would think would go along with that benefit that didn't turn out to be true. So this raises a question. When you do a large study like this and you measure a zillion things at the beginning and then you look at lots of different outcomes later on, you have a wonderful database. But that database people can play with and they can say well, I wonder if eating apricots causes heart disease or stroke. Now, I don't know if they actually ask the question about eating apricots, but if you play with the data and ask it many, many, many questions, statistically you're going to come up with something often that is abnormal, when in reality it isn't. From this long study there's been 2,300 published articles. Well, the way that happens is people are working with that database regularly, testing all sorts of hypotheses, and this was just one hypothesis that was tested and found to be interesting and positive. That doesn't mean it's true.
Speaker 1:So how do you sort out whether an observational study finding like this is true or not? Well, first of all, I don't get excited if it's presented at a meeting and it hasn't been peer-reviewed, published. But about 60 years ago there was an epidemiologist, somebody who studies the rates of disease and the causes of disease in England. This is where this epidemiologist was based. Who studies the rates of disease and the causes of disease in England? This is where this epidemiologist was based and his name was Sir Bradford Hill and he developed nine different criteria for causation.
Speaker 1:So when you look at an observational study and you find, oh look, apricots seem to be related to heart disease, you can ask yourself these sets of questions and that will make it more or less likely to be true. I'm not going to go through all nine. Maybe over the course of upcoming episodes I will, but I want to highlight a few. The first is when you see something like this, you have to ask yourself is it plausible? Now, if it was my hypothetical example of apricots causing heart disease, then I got to come up with a theory why might apricots do this? Well, in this scenario, is there a plausible relationship between oral health and a stroke or heart disease. And, as I walked through before, there is a plausible connection that poor oral health relates to bacteria. That bacteria could get in your body that could lead to inflammation. Inflammation leads to these types of problems. Okay, so there is a plausible relationship, so they get a point for that in my estimation. Well, the next criteria is how strong was that finding? You know, was it a 1% increase in risk or, in this case, a 20% or 50% increase? So that also ups our likelihood of causation.
Speaker 1:Now we get to the ones that they didn't do or what we don't know about this. The first is consistency. Bradford Hill criteria is well. Has it been reproduced by other investigators in other databases, in other areas of the country or the world? Well, the answer is no. There haven't been another study looking at flossing, and so it fails on this criteria.
Speaker 1:We've talked in the past about something like dose response. That means if you think something causes a problem like smoking and heart disease, is there a dose response relationship, meaning if you smoke one cigarette a day versus 10, versus 20, versus 40, if you think smoking is a problem, does it get more risky if you smoke more? So is there a dose-response relationship to flossing. Well, flossing once a week is better than nothing. Flossing once a day is even better. Flossing multiple times a day could even be better still. Well, that would be really important data, but we don't know, the study didn't talk about it, probably it wasn't measured, but that would help us. And again, as I've mentioned, I put all of this in a category of well, it's not published, it's not peer-reviewed. Will there ever be an RCT, a randomized controlled trial, to test this? I don't know. So we may be left with the Bradford Hill criteria and observational studies.
Speaker 1:Well, let's wrap up. Without a doubt, brushing and flossing are important for our mouth and oral health. Does oral health cause heart disease and stroke? It's really plausible. There's a lot of observational studies, but it's still an unanswered question. Third, it is uncertain whether flossing reduces our risk.
Speaker 1:Well, if you want to know what I do, I brush twice a day and I do this absolutely every day, and I floss religiously. I floss at the end of the day, when my mouth is full of junk and I can do a good job is I can sit and relax and do that. I've also found no science here that the water jet, the thing that sprays water at your teeth is really, really helpful. I can do all the mouth care I want and I still get junk coming out when I use the water jet, so I do that as well. Actually, I begin by gargling, then I do the water jet, then I brush my teeth and then I finish it off by flossing. This is just my once a day routine. In the morning I just brush Well, as always.
Speaker 1:I hope that you live long and well, that you live long and well and perhaps consider adding more flossing and brushing to your daily routine. It may or may not impact your likelihood of a stroke, but it will definitely improve your oral health and by itself that's a really good thing too. Until next time, take care. Thanks so much for listening to Live Long and Well with Dr Bobby. Until next time, take care. Want to receive my newsletter on practical and scientific ways to improve your health and longevity? Please visit me at drbobbilivelongandwellcom. That's Dr. As in D-R Bobby. Live long and wellcom.