By Robert H. Shmerling, MD
The burning question in the news last week was this: should you bother flossing?
The answer for decades has been “of course.” And it’s likely you’ve heard something similar from your dentist. I know I have.
But, while the importance of flossing may have been widely accepted, the evidence supporting it turns out to be surprisingly thin. At least that’s the conclusion of health experts who developed the recently released Dietary Guidelines for Americans, 2015-2020. These guidelines are issued every five years by the U.S. Department of Health and Humans Services and the U.S. Department of Agriculture “…to reflect the current body of scientific evidence on nutrition, food, and health.” The 2010 edition included this sentence:
“A combined approach of reducing the amount of time sugars and starches are in the mouth, drinking fluoridated water, and brushing and flossing teeth, is the most effective way to reduce dental caries.”
But, the latest edition leaves this sentence out. That’s because the authors of these guidelines could not find convincing evidence to support flossing, and the guidelines are supposed to be evidence-based. According to reviews of the evidence published in 2011 and 2015, there is minimal, short-term, and generally unreliable evidence that flossing might reduce gum inflammation, but no convincing evidence that it promotes plaque removal or prevents tooth decay or dental caries (cavities).
Is the lack of evidence for flossing big news?
I’ve seen several eye-grabbing headlines regarding this development, including:
- “Feeling Guilty About Not Flossing? Maybe There’s No Need” (New York Times)
- “Guilty No More: Flossing Doesn’t Work” (Mother Jones)
- “A big problem with flossing” (CBS News)
It is surprising to learn that there is so little evidence to support such a well-accepted bit of health dogma. Yet, there may be less here than meets the eye.
In fact, I think these headlines (and some of the comments I’ve heard from friends and family) miss the mark on this flossing kerfuffle. There’s a saying in the science world that “absence of proof isn’t proof of absence.” That is, just because the evidence isn’t there doesn’t mean an idea is wrong. Unproven is unproven, not disproven!
A cousin emailed me to say “Good, now I can feel less guilty about not flossing.” I’m all for people feeling empowered with their health decisions (especially if they are well-informed). But the experts who removed the flossing recommendations from the dietary guidelines did not find flossing was useless. They only found that flossing had never been well-studied and that the evidence to date was inconclusive. If my cousin has gum disease, flossing might be important for his oral health. Flossing is low-cost, low-risk, and has potential (and biologically plausible) health benefits; it seems premature to conclude it is useless. In fact, it may very well be a good idea just waiting to be well-studied.
Flossing in the dietary guidelines? What about brushing?
And am I the only one that finds it odd that flossing was even mentioned in a compilation of dietary guidelines? They are supposed to be about what you eat, not how you care for your teeth! And where is the outrage about brushing? That was removed as well but no one seems to be worrying much about that; perhaps it’s because people don’t mind brushing as much as they mind flossing. In fact, a 2015 survey found that 14% of respondents would rather clean a toilet than floss their teeth each day.
So to floss, or not floss (without guilt)?
The obvious next step is to recommend that researchers study the health impact of flossing. With a well-funded, well-designed study, it may be easy to prove that, in fact, flossing is good for your oral health, and I would not be surprised if it turned out to be good for you in other ways, since gum disease has been linked to an increased risk of cardiovascular disease, diabetes, and stroke. But that’s getting ahead of the story; let’s first prove that daily flossing is at least good for your oral health. I’m not going to wait for the research; I’m going to keep flossing. I hope my cousin does too.
(Published with permission from Harvard Gazette.)
