April 15, 2025 • 27 mins
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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Be cautious with headlines drawn from unpublished conference abstracts—they’re a starting point for inquiry, not a reason to change behavior just yet.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.
Mark as Played
Transcript
Episode Transcript
Available transcripts are automatically generated. Complete accuracy is not guaranteed.
Speaker 1 (00:01):
Can flossing your teeth really reduce your risk of
stroke?
Recent headlines suggest thatit may be true, but does the
evidence support this?
Is it even biologicallyplausible?
Let's explore what we know and,most importantly, what we don't
(00:23):
know.
Hi, I'm Dr Bobby Du Bois andwelcome to Live Long and Well, a
(00:43):
podcast where we will talkabout what you can do to live as
long as possible and with asmuch energy and figure that you
wish.
Together, we will explore whatpractical and evidence-supported
steps you can take.
Come join me on this veryimportant journey and I hope
that you feel empowered alongthe way.
I'm a physician, ironman,triathlete and have published
(01:06):
several hundred scientificstudies.
I'm honored to be your guide.
Welcome, my wonderful listenersto episode 35.
Can flossing reduce your risk ofstroke?
Well, it's a fascinatingquestion and we, of course,
(01:29):
don't want to get a stroke.
And there was a recent studyand lots of headlines in all the
news media that said flossingreduces our risk of stroke by 20
to 50 percent, depending uponthe type of stroke.
Now, this was based on apresentation at the American
(01:52):
Stroke Association'sInternational Conference on
Stroke and it was widely pickedup by the media, by the New York
Post, the San FranciscoChronicle, youtube post, the San
Francisco Chronicle, youtubeTimes, uk Jerusalem post, and we
are going to dive into thisstudy shortly.
(02:16):
But why discuss this topic?
Well, the headline is reallycatching Flossing reduces our
risk of a stroke.
Now the question, of course, isis there anything to this and
beyond just this study?
Are there lessons to glean fromall the headlines?
All the attention?
Are those lessons things thatcan teach us how to approach
(02:39):
future headlines and whether tobelieve it or not?
Now, as you may recall, inepisode 22, health headlines
helpful, harmful or just plainconfusing we explored a headline
that was worrisome, thatintermittent fasting caused
heart attacks, and now we did abit of myth busting there and we
(03:02):
showed a lot of the problemswith that study.
Is it the same scenario here,where this hype exceeds what the
evidence tells us?
Well, stay tuned, and we'regoing to figure this out.
As I was thinking aboutexplaining to you, my listeners,
why are we doing an episodelike this, I realized I was
(03:25):
destined.
It was my destiny to do thisepisode Now.
I didn't know it 30 years ago,when I was visiting my dentist
and at the time she had justcome back from a conference in
Hawaii.
So this is in the 1990s or soand at that conference,
(03:50):
basically, she learned how oralhealth, mouth issues, could
cause heart disease.
And I'm an internist, I'm aphysician, she's a dentist and
she's telling me about heartdisease and she was saying, oh,
we must brush our teeth andfloss our teeth and that will
potentially help the risk ofheart disease.
(04:12):
And she was very excited aboutthis and told all of her
patients my wife and my kids andeverybody else.
It turns out she may have beenahead of the medical community
Back 30 years ago.
This was not something that wascommonly discussed.
Well, we'll come back to thisas well.
Before we dive into the content,I have a request.
(04:35):
This is episode 35, so I'vebeen doing a whole bunch of
these and I would love to getfeedback from you about how I'm
doing the topics you like, thetopics you want more of, and
there's a brief, briefquestionnaire.
It'll take you like two minutesand the link is in the show
(04:55):
notes.
So please, if you can do, takea couple of minutes and give me
that feedback.
Some of the questions I reallywant to learn from you do you
like episodes that summarizeevidence on a topic Like is
there evidence that sleep isimportant or that nutrition
matters.
Do you like myth-busting?
(05:16):
In some cases maybe today'sepisode is myth-busting
Certainly the one on seed oilsfits into that Do you like that
type?
How about the ones where Ishare a personal health journey,
like the one I did recently onmy needing a brain MRI and what
happened?
Also, the framework episodes Doyou Like your Doctor?
(05:40):
Where I sort of lay out how tothink through things.
So I'd love to get your inputon that, on any new topics you
might suggest and, mostimportantly, 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?
(06:01):
I have tried to avoid many ofthe other health podcasts length
of an hour hour and a half twohours, all right.
Well, let's dive into our studyfor today and our topic today
Can flossing reduce our risk ofa stroke?
Now some stroke facts, becausestroke is not something we talk
(06:24):
about all the time.
Heart attacks we talk, notsomething we talk about all the
time.
Heart attacks we talk about, wehear about all the time.
Stroke for a while hasn't beenreally front and center Yet.
There's about 800,000 strokesthat happen in the US every year
, and about every 40 secondsthere's a stroke, and about
every three minutes somebodydies of a stroke.
(06:48):
Equally importantly, strokecauses major disability.
You might not be able to moveon one side or a part of your
body, you might not be able tospeak.
Well, all sorts of disabilitiescan come out of it.
So it's a really, reallyimportant topic and could
(07:09):
something as simple, really assimple, as flossing help us?
Well, we need to talk a littlebit about your mouth, oral
health and how this possiblesolution or reduction in risk
could occur.
Well, we have, at any one pointin time, about a billion
(07:33):
bacteria in our mouths, just onour gums, on our teeth, in the
saliva, and it is known quiteclearly that if you brush or
you're chewing, bacteria can anddo get into our bloodstream.
That, of course, doesn't soundvery good.
Well, if bacteria get in ourbloodstream, they could cause
(07:56):
direct damage, meaning thosebacteria could go to other parts
of our body and that couldcreate problems for us.
Or and I think this is perhapsmore likely that the bacteria in
our mouth that get in ourbloodstream cause what I would
call indirect damage, and thatindirect damage is that it
(08:19):
creates an inflammation, aninflammatory reaction and
inflammation has been associatedwith heart attacks, cancer,
metabolic disorders and the like.
So this issue of the damagefrom the bacteria is really a
(08:39):
sensual question.
What we also know is that ifyour gums that surround and hold
in your teeth, if they areinflamed, if they are infected,
more bacteria are around andmore bacteria can get into our
body and cause problems.
We also know good studies onthis that if you brush and floss
(09:04):
, it can reduce it does reduceyour risk of gum disease.
So theoretically now we'rebuilding an argument that the
bacteria in our mouth could getin our bloodstream, could cause
inflammation, and brushing andflossing has been shown to
(09:27):
reduce that risk of inflammationin blood bacteria.
Now we haven't made the leapyet to stroke or heart disease,
but at least we're beginning tobuild a story and we have a lot
of room for improvement in oralhealth.
(09:47):
Studies show that Americans dobrush pretty regularly, but they
don't floss very regularly.
Here's some data.
So in a study that waspublished, 90% of us do brush at
least once a day and 60% of usbrush more than once a day.
(10:08):
I'm a twice a day brushermyself, religiously, in the
morning and at night.
Now flossing we're not so goodas Americans about flossing.
A third of us don't floss atall.
A third of us floss basicallyabout once a week and only a
(10:30):
third of us floss on a dailybasis.
Well, I'm a nightly flosser andI find that it makes a huge
difference that even though I'vebrushed and gargled with
mouthwash, there's still a lotof junk on my teeth.
I've also found this is asimple hack that if you floss in
(10:50):
front of a mirror close up,like makeup mirror boy, you make
a lot better job of it than ifyou just floss in general, not
looking at a mirror or evenlooking at your bathroom mirror.
So if flossing were to matterand really if the study were
true, gosh, there's a tremendousopportunity here, because a lot
(11:13):
of us don't floss or don'tfloss really well.
Okay, let's examine some more ofthe evidence connecting oral
health with heart disease.
Is it that a poor mouth, withgingivitis and other things,
that it causes a heart diseaseor stroke, or is it just common
(11:36):
factors?
So perhaps the mouth doesn'tcause stroke and heart disease.
Perhaps it's things that hurtthe mouth also hurt other parts
of your body.
So here's a perfect exampleSmoking.
Smoking, we know, raises yourrisk of a heart disease or
stroke.
(11:56):
Smoking also worsens your oralhealth, so it may not be that
the mouth is causing the problem.
It just may be there's a commonunderlying factor like smoking
or diabetes or getting older.
Or, as the article mightsuggest to us, it is the
(12:20):
presence of the problem in ourmouth, your bacteria and gum
disease, that causes heartdisease or stroke.
Now, as we've talked about manytimes, correlation doesn't mean
causation.
Just because we see that peoplewith strokes have mouth disease
or people with heart attackshave mouth disease doesn't mean
(12:43):
one causes the other.
Well, the American HeartAssociation reviewed the
evidence and this is how theysaw it.
They said well, there's a lotof observational studies that
support the relationship betweenmouth health and heart health,
(13:05):
but they summarize that thoseobservational studies don't say
it's causative.
It just means that they arepotentially connected.
Unfortunately, there haven'tbeen any randomized controlled
trials where some people getgood oral care, some people
don't.
We follow them for 20, 30 yearsand we see who gets heart
(13:27):
disease or strokes.
Unfortunately, that study hasnever been done.
I don't know if it ever will bedone.
Well, if the mouth and the heart, mouth and the stroke are
causative, that the problems inone area create problems in the
other.
The theory is that it's due to,as I mentioned earlier,
(13:49):
inflammation.
Now we do have pretty good datathat inflammation is associated
with heart disease.
One of the blood things thatyour doctor may order for you is
called a CRP or C-reactiveprotein, or high-sensitivity CRP
, and it's been shown many timesthat if that blood level which
(14:13):
reflects inflammation iselevated, there's a much higher
likelihood of having heartdisease later on.
And there's reasonable datathat said, if you improve your
oral health, it lowers thoseinflammatory markers.
So we're starting to build acase that oral health relates to
(14:38):
inflammation, the case thatoral health relates to
inflammation.
We believe inflammation relatesto heart disease and the like.
But again, this is all justbuilding a theoretical argument.
All right, before we get toflossing, there is some data on
toothbrush, brushing your teethand heart disease.
(15:01):
And if you brush just once aday or less than once a day, you
have twice the risk of heartdisease than if you brush two or
more times a day.
Again, all this evidence isobservational.
We don't have the randomizedcontrolled trial, so we can't
(15:24):
officially say there's a causeand effect relationship, but it
is intriguing and maybe somedaythere will be that randomized
trial.
Okay, now we are ready to go onto the flossing study and to
see whether the headlines aretrue or likely true and if not,
(15:46):
what does it teach us aboutreading headlines carefully and
understanding whether to believeit or not?
Well, the title of the studywas regular dental flossing may
lower risk of stroke from bloodclots and irregular heartbeats.
(16:06):
This was a study, as I mentioned, that had been presented at a
conference and it was from whatwas called the ERIC study
atherosclerosis risk incommunities.
This is a large study that'sbeen tracking over 6,000 people
over 25 years, and the purposeof this big study was to see
(16:27):
things that might relate toheart disease, so things like
they might have measured 25years at the beginning of the
study, whether you smoke,whether you exercise, all sorts
of different things and some ofthe things they asked related to
oral health, and what theyfound was about two-thirds of
(16:49):
people in this long-term studyagain, not a randomized trial,
just an observational studyabout two-thirds of those folks
did, in fact, floss, and thosewho flossed when they followed
them over time had a 20% to 50%lower risk of a stroke
(17:12):
Incredible.
Now, it varied by type ofstroke.
That flossing didn't reduceyour risk of all types of
strokes, but important,important ones.
Interestingly, they didn't findbenefit for brushing and they
didn't find benefit for visitingyour dentist.
So this is the first inklingthat maybe this study isn't as
(17:37):
valid as the headlines wouldsuggest.
But if it's true and there isthat large reduction in stroke
simply by flossing, maybe therecould be as many as 50 to
150,000 fewer strokes in theUnited States each year.
That is extraordinary.
(17:58):
And why is this not what thefiremen call a five-alarm fire?
Now, when there are fires,there's alerts that go out and a
five-alarm fire means the fireis out of control.
Bring every resource you have,let's fight this fire.
So why isn't this study andflossing a five alarm fire where
(18:25):
everybody should be talkingabout it?
Well, I have concerns with thisstudy, not surprisingly.
That's why I'm doing thisepisode.
Surprisingly, that's why I'mdoing this episode.
Like our episode on healthheadlines and intermittent
fasting causing death from heartdisease, this set of headlines
and study has some of the sameproblems.
(18:49):
This was not a peer-reviewedpublished article.
It was merely an abstract thatwas presented at a conference.
So somebody wrote up aparagraph or two about the study
and presented it at a meeting,and maybe there were a few
(19:09):
different questions, but nobodyhas seen the full data, how the
study was done, sent it out toother experts and ultimately
undergo peer review and thenpublication in a peer-reviewed
journal.
None of this happened.
I also mentioned that flossingseemed to help, but brushing and
(19:35):
going to the dentist two otherthings that we would think would
go along with that benefit thatdidn't turn out to be true.
So this raises a question.
When you do a large study likethis and you measure a zillion
things at the beginning and thenyou look at lots of different
outcomes later on, you have awonderful database.
(19:58):
But that database people canplay with and they can say well,
I wonder if eating apricotscauses heart disease or stroke.
Now, I don't know if theyactually ask the question about
eating apricots, but if you playwith the data and ask it many,
many, many questions,statistically you're going to
come up with something oftenthat is abnormal, when in
(20:21):
reality it isn't.
From this long study there'sbeen 2,300 published articles.
Well, the way that happens ispeople are working with that
database regularly, testing allsorts of hypotheses, and this
was just one hypothesis that wastested and found to be
(20:46):
interesting and positive.
That doesn't mean it's true.
So how do you sort out whetheran observational study finding
like this is true or not?
Well, first of all, I don't getexcited if it's presented at a
meeting and it hasn't beenpeer-reviewed, published.
But about 60 years ago therewas an epidemiologist, somebody
(21:11):
who studies the rates of diseaseand the causes of disease in
England.
This is where thisepidemiologist was based.
Who studies the rates ofdisease and the causes of
disease in England?
This is where thisepidemiologist was based and his
name was Sir Bradford Hill andhe developed nine different
criteria for causation.
So when you look at anobservational study and you find
(21:32):
, oh look, apricots seem to berelated to heart disease, you
can ask yourself these sets ofquestions and that will make it
more or less likely to be true.
I'm not going to go through allnine.
Maybe over the course ofupcoming episodes I will, but I
(21:52):
want to highlight a few.
The first is when you seesomething like this, you have to
ask yourself is it plausible?
Now, if it was my hypotheticalexample of apricots causing
heart disease, then I got tocome up with a theory why might
apricots do this?
Well, in this scenario, isthere a plausible relationship
(22:17):
between oral health and a strokeor heart disease.
And, as I walked through before, there is a plausible
connection that poor oral healthrelates to bacteria.
That bacteria could get in yourbody that could lead to
inflammation.
Inflammation leads to thesetypes of problems.
Okay, so there is a plausiblerelationship, so they get a
(22:40):
point for that in my estimation.
Well, the next criteria is howstrong was that finding?
You know, was it a 1% increasein risk or, in this case, a 20%
or 50% increase?
So that also ups our likelihoodof causation.
(23:02):
Now we get to the ones that theydidn't do or what we don't know
about this.
The first is consistency.
Bradford Hill criteria is well.
Has it been reproduced by otherinvestigators in other
databases, in other areas of thecountry or the world?
(23:22):
Well, the answer is no.
There haven't been anotherstudy looking at flossing, and
so it fails on this criteria.
We've talked in the past aboutsomething like dose response.
That means if you thinksomething causes a problem like
smoking and heart disease, isthere a dose response
(23:46):
relationship, meaning if yousmoke one cigarette a day versus
10, versus 20, versus 40, ifyou think smoking is a problem,
does it get more risky if yousmoke more?
So is there a dose-responserelationship to flossing.
Well, flossing once a week isbetter than nothing.
(24:07):
Flossing once a day is evenbetter.
Flossing multiple times a daycould even be better still.
Well, that would be reallyimportant data, but we don't
know, the study didn't talkabout it, probably it wasn't
measured, but that would help us.
And again, as I've mentioned, Iput all of this in a category
(24:29):
of well, it's not published,it's not peer-reviewed.
Will there ever be an RCT, arandomized controlled trial, to
test this?
I don't know.
So we may be left with theBradford Hill criteria and
observational studies.
(24:51):
Well, let's wrap up.
Without a doubt, brushing andflossing are important for our
mouth and oral health.
Does oral health cause heartdisease and stroke?
It's really plausible.
There's a lot of observationalstudies, but it's still an
(25:11):
unanswered question.
Third, it is uncertain whetherflossing reduces our risk.
Well, if you want to know what Ido, 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
(25:32):
and I can do a good job is I cansit and relax and do that.
I've also found no science herethat the water jet, the thing
that sprays water at your teethis really, really helpful.
I can do all the mouth care Iwant and I still get junk coming
out when I use the water jet,so I do that as well.
(25:55):
Actually, I begin by gargling,then I do the water jet, then I
brush my teeth and then I finishit off by flossing.
This is just my once a dayroutine.
In the morning I just brushWell, as always.
I hope that you live long andwell, that you live long and
(26:21):
well and perhaps consider addingmore flossing and brushing to
your daily routine.
It may or may not impact yourlikelihood of a stroke, but it
will definitely improve youroral health and by itself that's
a really good thing too.
Until next time, take care.
Thanks so much for listening toLive Long and Well with Dr
(26:59):
Bobby.
Until next time, take care.
Want to receive my newsletteron practical and scientific ways
to improve your health andlongevity?
Please visit me atdrbobbilivelongandwellcom.
That's Dr.
As in D-R Bobby.
Live long and wellcom.
Can flossing your teeth really reduce your risk of
stroke?
Recent headlines suggest thatit may be true, but does the
evidence support this?
Is it even biologicallyplausible?
Let's explore what we know and,most importantly, what we don't
(00:23):
know.
Hi, I'm Dr Bobby Du Bois andwelcome to Live Long and Well, a
(00:43):
podcast where we will talkabout what you can do to live as
long as possible and with asmuch energy and figure that you
wish.
Together, we will explore whatpractical and evidence-supported
steps you can take.
Come join me on this veryimportant journey and I hope
that you feel empowered alongthe way.
I'm a physician, ironman,triathlete and have published
(01:06):
several hundred scientificstudies.
I'm honored to be your guide.
Welcome, my wonderful listenersto episode 35.
Can flossing reduce your risk ofstroke?
Well, it's a fascinatingquestion and we, of course,
(01:29):
don't want to get a stroke.
And there was a recent studyand lots of headlines in all the
news media that said flossingreduces our risk of stroke by 20
to 50 percent, depending uponthe type of stroke.
Now, this was based on apresentation at the American
(01:52):
Stroke Association'sInternational Conference on
Stroke and it was widely pickedup by the media, by the New York
Post, the San FranciscoChronicle, youtube post, the San
Francisco Chronicle, youtubeTimes, uk Jerusalem post, and we
are going to dive into thisstudy shortly.
(02:16):
But why discuss this topic?
Well, the headline is reallycatching Flossing reduces our
risk of a stroke.
Now the question, of course, isis there anything to this and
beyond just this study?
Are there lessons to glean fromall the headlines?
All the attention?
Are those lessons things thatcan teach us how to approach
(02:39):
future headlines and whether tobelieve it or not?
Now, as you may recall, inepisode 22, health headlines
helpful, harmful or just plainconfusing we explored a headline
that was worrisome, thatintermittent fasting caused
heart attacks, and now we did abit of myth busting there and we
(03:02):
showed a lot of the problemswith that study.
Is it the same scenario here,where this hype exceeds what the
evidence tells us?
Well, stay tuned, and we'regoing to figure this out.
As I was thinking aboutexplaining to you, my listeners,
why are we doing an episodelike this, I realized I was
(03:25):
destined.
It was my destiny to do thisepisode Now.
I didn't know it 30 years ago,when I was visiting my dentist
and at the time she had justcome back from a conference in
Hawaii.
So this is in the 1990s or soand at that conference,
(03:50):
basically, she learned how oralhealth, mouth issues, could
cause heart disease.
And I'm an internist, I'm aphysician, she's a dentist and
she's telling me about heartdisease and she was saying, oh,
we must brush our teeth andfloss our teeth and that will
potentially help the risk ofheart disease.
(04:12):
And she was very excited aboutthis and told all of her
patients my wife and my kids andeverybody else.
It turns out she may have beenahead of the medical community
Back 30 years ago.
This was not something that wascommonly discussed.
Well, we'll come back to thisas well.
Before we dive into the content,I have a request.
(04:35):
This is episode 35, so I'vebeen doing a whole bunch of
these and I would love to getfeedback from you about how I'm
doing the topics you like, thetopics you want more of, and
there's a brief, briefquestionnaire.
It'll take you like two minutesand the link is in the show
(04:55):
notes.
So please, if you can do, takea couple of minutes and give me
that feedback.
Some of the questions I reallywant to learn from you do you
like episodes that summarizeevidence on a topic Like is
there evidence that sleep isimportant or that nutrition
matters.
Do you like myth-busting?
(05:16):
In some cases maybe today'sepisode is myth-busting
Certainly the one on seed oilsfits into that Do you like that
type?
How about the ones where Ishare a personal health journey,
like the one I did recently onmy needing a brain MRI and what
happened?
Also, the framework episodes Doyou Like your Doctor?
(05:40):
Where I sort of lay out how tothink through things.
So I'd love to get your inputon that, on any new topics you
might suggest and, mostimportantly, 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?
(06:01):
I have tried to avoid many ofthe other health podcasts length
of an hour hour and a half twohours, all right.
Well, let's dive into our studyfor today and our topic today
Can flossing reduce our risk ofa stroke?
Now some stroke facts, becausestroke is not something we talk
(06:24):
about all the time.
Heart attacks we talk, notsomething we talk about all the
time.
Heart attacks we talk about, wehear about all the time.
Stroke for a while hasn't beenreally front and center Yet.
There's about 800,000 strokesthat happen in the US every year
, and about every 40 secondsthere's a stroke, and about
every three minutes somebodydies of a stroke.
(06:48):
Equally importantly, strokecauses major disability.
You might not be able to moveon one side or a part of your
body, you might not be able tospeak.
Well, all sorts of disabilitiescan come out of it.
So it's a really, reallyimportant topic and could
(07:09):
something as simple, really assimple, as flossing help us?
Well, we need to talk a littlebit about your mouth, oral
health and how this possiblesolution or reduction in risk
could occur.
Well, we have, at any one pointin time, about a billion
(07:33):
bacteria in our mouths, just onour gums, on our teeth, in the
saliva, and it is known quiteclearly that if you brush or
you're chewing, bacteria can anddo get into our bloodstream.
That, of course, doesn't soundvery good.
Well, if bacteria get in ourbloodstream, they could cause
(07:56):
direct damage, meaning thosebacteria could go to other parts
of our body and that couldcreate problems for us.
Or and I think this is perhapsmore likely that the bacteria in
our mouth that get in ourbloodstream cause what I would
call indirect damage, and thatindirect damage is that it
(08:19):
creates an inflammation, aninflammatory reaction and
inflammation has been associatedwith heart attacks, cancer,
metabolic disorders and the like.
So this issue of the damagefrom the bacteria is really a
(08:39):
sensual question.
What we also know is that ifyour gums that surround and hold
in your teeth, if they areinflamed, if they are infected,
more bacteria are around andmore bacteria can get into our
body and cause problems.
We also know good studies onthis that if you brush and floss
(09:04):
, it can reduce it does reduceyour risk of gum disease.
So theoretically now we'rebuilding an argument that the
bacteria in our mouth could getin our bloodstream, could cause
inflammation, and brushing andflossing has been shown to
(09:27):
reduce that risk of inflammationin blood bacteria.
Now we haven't made the leapyet to stroke or heart disease,
but at least we're beginning tobuild a story and we have a lot
of room for improvement in oralhealth.
(09:47):
Studies show that Americans dobrush pretty regularly, but they
don't floss very regularly.
Here's some data.
So in a study that waspublished, 90% of us do brush at
least once a day and 60% of usbrush more than once a day.
(10:08):
I'm a twice a day brushermyself, religiously, in the
morning and at night.
Now flossing we're not so goodas Americans about flossing.
A third of us don't floss atall.
A third of us floss basicallyabout once a week and only a
(10:30):
third of us floss on a dailybasis.
Well, I'm a nightly flosser andI find that it makes a huge
difference that even though I'vebrushed and gargled with
mouthwash, there's still a lotof junk on my teeth.
I've also found this is asimple hack that if you floss in
(10:50):
front of a mirror close up,like makeup mirror boy, you make
a lot better job of it than ifyou just floss in general, not
looking at a mirror or evenlooking at your bathroom mirror.
So if flossing were to matterand really if the study were
true, gosh, there's a tremendousopportunity here, because a lot
(11:13):
of us don't floss or don'tfloss really well.
Okay, let's examine some more ofthe evidence connecting oral
health with heart disease.
Is it that a poor mouth, withgingivitis and other things,
that it causes a heart diseaseor stroke, or is it just common
(11:36):
factors?
So perhaps the mouth doesn'tcause stroke and heart disease.
Perhaps it's things that hurtthe mouth also hurt other parts
of your body.
So here's a perfect exampleSmoking.
Smoking, we know, raises yourrisk of a heart disease or
stroke.
(11:56):
Smoking also worsens your oralhealth, so it may not be that
the mouth is causing the problem.
It just may be there's a commonunderlying factor like smoking
or diabetes or getting older.
Or, as the article mightsuggest to us, it is the
(12:20):
presence of the problem in ourmouth, your bacteria and gum
disease, that causes heartdisease or stroke.
Now, as we've talked about manytimes, correlation doesn't mean
causation.
Just because we see that peoplewith strokes have mouth disease
or people with heart attackshave mouth disease doesn't mean
(12:43):
one causes the other.
Well, the American HeartAssociation reviewed the
evidence and this is how theysaw it.
They said well, there's a lotof observational studies that
support the relationship betweenmouth health and heart health,
(13:05):
but they summarize that thoseobservational studies don't say
it's causative.
It just means that they arepotentially connected.
Unfortunately, there haven'tbeen any randomized controlled
trials where some people getgood oral care, some people
don't.
We follow them for 20, 30 yearsand we see who gets heart
(13:27):
disease or strokes.
Unfortunately, that study hasnever been done.
I don't know if it ever will bedone.
Well, if the mouth and the heart, mouth and the stroke are
causative, that the problems inone area create problems in the
other.
The theory is that it's due to,as I mentioned earlier,
(13:49):
inflammation.
Now we do have pretty good datathat inflammation is associated
with heart disease.
One of the blood things thatyour doctor may order for you is
called a CRP or C-reactiveprotein, or high-sensitivity CRP
, and it's been shown many timesthat if that blood level which
(14:13):
reflects inflammation iselevated, there's a much higher
likelihood of having heartdisease later on.
And there's reasonable datathat said, if you improve your
oral health, it lowers thoseinflammatory markers.
So we're starting to build acase that oral health relates to
(14:38):
inflammation, the case thatoral health relates to
inflammation.
We believe inflammation relatesto heart disease and the like.
But again, this is all justbuilding a theoretical argument.
All right, before we get toflossing, there is some data on
toothbrush, brushing your teethand heart disease.
(15:01):
And if you brush just once aday or less than once a day, you
have twice the risk of heartdisease than if you brush two or
more times a day.
Again, all this evidence isobservational.
We don't have the randomizedcontrolled trial, so we can't
(15:24):
officially say there's a causeand effect relationship, but it
is intriguing and maybe somedaythere will be that randomized
trial.
Okay, now we are ready to go onto the flossing study and to
see whether the headlines aretrue or likely true and if not,
(15:46):
what does it teach us aboutreading headlines carefully and
understanding whether to believeit or not?
Well, the title of the studywas regular dental flossing may
lower risk of stroke from bloodclots and irregular heartbeats.
(16:06):
This was a study, as I mentioned, that had been presented at a
conference and it was from whatwas called the ERIC study
atherosclerosis risk incommunities.
This is a large study that'sbeen tracking over 6,000 people
over 25 years, and the purposeof this big study was to see
(16:27):
things that might relate toheart disease, so things like
they might have measured 25years at the beginning of the
study, whether you smoke,whether you exercise, all sorts
of different things and some ofthe things they asked related to
oral health, and what theyfound was about two-thirds of
(16:49):
people in this long-term studyagain, not a randomized trial,
just an observational studyabout two-thirds of those folks
did, in fact, floss, and thosewho flossed when they followed
them over time had a 20% to 50%lower risk of a stroke
(17:12):
Incredible.
Now, it varied by type ofstroke.
That flossing didn't reduceyour risk of all types of
strokes, but important,important ones.
Interestingly, they didn't findbenefit for brushing and they
didn't find benefit for visitingyour dentist.
So this is the first inklingthat maybe this study isn't as
(17:37):
valid as the headlines wouldsuggest.
But if it's true and there isthat large reduction in stroke
simply by flossing, maybe therecould be as many as 50 to
150,000 fewer strokes in theUnited States each year.
That is extraordinary.
(17:58):
And why is this not what thefiremen call a five-alarm fire?
Now, when there are fires,there's alerts that go out and a
five-alarm fire means the fireis out of control.
Bring every resource you have,let's fight this fire.
So why isn't this study andflossing a five alarm fire where
(18:25):
everybody should be talkingabout it?
Well, I have concerns with thisstudy, not surprisingly.
That's why I'm doing thisepisode.
Surprisingly, that's why I'mdoing this episode.
Like our episode on healthheadlines and intermittent
fasting causing death from heartdisease, this set of headlines
and study has some of the sameproblems.
(18:49):
This was not a peer-reviewedpublished article.
It was merely an abstract thatwas presented at a conference.
So somebody wrote up aparagraph or two about the study
and presented it at a meeting,and maybe there were a few
(19:09):
different questions, but nobodyhas seen the full data, how the
study was done, sent it out toother experts and ultimately
undergo peer review and thenpublication in a peer-reviewed
journal.
None of this happened.
I also mentioned that flossingseemed to help, but brushing and
(19:35):
going to the dentist two otherthings that we would think would
go along with that benefit thatdidn't turn out to be true.
So this raises a question.
When you do a large study likethis and you measure a zillion
things at the beginning and thenyou look at lots of different
outcomes later on, you have awonderful database.
(19:58):
But that database people canplay with and they can say well,
I wonder if eating apricotscauses heart disease or stroke.
Now, I don't know if theyactually ask the question about
eating apricots, but if you playwith the data and ask it many,
many, many questions,statistically you're going to
come up with something oftenthat is abnormal, when in
(20:21):
reality it isn't.
From this long study there'sbeen 2,300 published articles.
Well, the way that happens ispeople are working with that
database regularly, testing allsorts of hypotheses, and this
was just one hypothesis that wastested and found to be
(20:46):
interesting and positive.
That doesn't mean it's true.
So how do you sort out whetheran observational study finding
like this is true or not?
Well, first of all, I don't getexcited if it's presented at a
meeting and it hasn't beenpeer-reviewed, published.
But about 60 years ago therewas an epidemiologist, somebody
(21:11):
who studies the rates of diseaseand the causes of disease in
England.
This is where thisepidemiologist was based.
Who studies the rates ofdisease and the causes of
disease in England?
This is where thisepidemiologist was based and his
name was Sir Bradford Hill andhe developed nine different
criteria for causation.
So when you look at anobservational study and you find
(21:32):
, oh look, apricots seem to berelated to heart disease, you
can ask yourself these sets ofquestions and that will make it
more or less likely to be true.
I'm not going to go through allnine.
Maybe over the course ofupcoming episodes I will, but I
(21:52):
want to highlight a few.
The first is when you seesomething like this, you have to
ask yourself is it plausible?
Now, if it was my hypotheticalexample of apricots causing
heart disease, then I got tocome up with a theory why might
apricots do this?
Well, in this scenario, isthere a plausible relationship
(22:17):
between oral health and a strokeor heart disease.
And, as I walked through before, there is a plausible
connection that poor oral healthrelates to bacteria.
That bacteria could get in yourbody that could lead to
inflammation.
Inflammation leads to thesetypes of problems.
Okay, so there is a plausiblerelationship, so they get a
(22:40):
point for that in my estimation.
Well, the next criteria is howstrong was that finding?
You know, was it a 1% increasein risk or, in this case, a 20%
or 50% increase?
So that also ups our likelihoodof causation.
(23:02):
Now we get to the ones that theydidn't do or what we don't know
about this.
The first is consistency.
Bradford Hill criteria is well.
Has it been reproduced by otherinvestigators in other
databases, in other areas of thecountry or the world?
(23:22):
Well, the answer is no.
There haven't been anotherstudy looking at flossing, and
so it fails on this criteria.
We've talked in the past aboutsomething like dose response.
That means if you thinksomething causes a problem like
smoking and heart disease, isthere a dose response
(23:46):
relationship, meaning if yousmoke one cigarette a day versus
10, versus 20, versus 40, ifyou think smoking is a problem,
does it get more risky if yousmoke more?
So is there a dose-responserelationship to flossing.
Well, flossing once a week isbetter than nothing.
(24:07):
Flossing once a day is evenbetter.
Flossing multiple times a daycould even be better still.
Well, that would be reallyimportant data, but we don't
know, the study didn't talkabout it, probably it wasn't
measured, but that would help us.
And again, as I've mentioned, Iput all of this in a category
(24:29):
of well, it's not published,it's not peer-reviewed.
Will there ever be an RCT, arandomized controlled trial, to
test this?
I don't know.
So we may be left with theBradford Hill criteria and
observational studies.
(24:51):
Well, let's wrap up.
Without a doubt, brushing andflossing are important for our
mouth and oral health.
Does oral health cause heartdisease and stroke?
It's really plausible.
There's a lot of observationalstudies, but it's still an
(25:11):
unanswered question.
Third, it is uncertain whetherflossing reduces our risk.
Well, if you want to know what Ido, 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
(25:32):
and I can do a good job is I cansit and relax and do that.
I've also found no science herethat the water jet, the thing
that sprays water at your teethis really, really helpful.
I can do all the mouth care Iwant and I still get junk coming
out when I use the water jet,so I do that as well.
(25:55):
Actually, I begin by gargling,then I do the water jet, then I
brush my teeth and then I finishit off by flossing.
This is just my once a dayroutine.
In the morning I just brushWell, as always.
I hope that you live long andwell, that you live long and
(26:21):
well and perhaps consider addingmore flossing and brushing to
your daily routine.
It may or may not impact yourlikelihood of a stroke, but it
will definitely improve youroral health and by itself that's
a really good thing too.
Until next time, take care.
Thanks so much for listening toLive Long and Well with Dr
(26:59):
Bobby.
Until next time, take care.
Want to receive my newsletteron practical and scientific ways
to improve your health andlongevity?
Please visit me atdrbobbilivelongandwellcom.
That's Dr.
As in D-R Bobby.
Live long and wellcom.
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