Why put fluoride in the water? Scientists weigh in

Audio transcript

SPEAKER 1: You’re listening to Short Wave from NPR.

EMILY KWONG: Hey, Short Waivers, Emily Kwong here. I’m back again with Pien Huang.

PIEN HUANG: Hello, hello.

KWONG: To look at what is in our drinking water. This time, fluoride.

HUANG: Yep, we’re talking fluoride, which is a topic that NPR has covered in drinking water around the US for literally decades. Fluoride is a very common mineral that occurs naturally in almost all soil, in water, even in many rocks.

KWONG: I didn’t know that. Fluoride hanging out in the rocks. OK.

HUANG: And most people in the US get fluoridated drinking water. It’s added to the water to prevent tooth decay and cavities. The current US Public Health Service recommendation is 0.7 parts per million, optimally, which is 3 drops in a 55-gallon barrel.

KWONG: OK, not higher, not lower. Just 0.7 parts per million.

HUANG: Right, Emily. And it used to be a range, but in 2015 it was revised down to the standard minimum 0.7 parts per million because there were concerns that, it levels higher than that, it could be causing dental fluorosis, which is streaking or mottling on kids teeth.

KWONG: Yeah, I mean, growing up, fluoride was always kind of unquestioned. It was like considered one of the greatest public health achievements of the 20th century.

HUANG: And it still is, Emily. But a debate is evolving over whether the risks and the benefits of fluoride have changed. So back in August 2024, part of the National Institutes of Health, called the National Toxicology Program, released a big report. It was over 300 pages long, and it linked high levels of fluoride exposure with a slight decline in children’s IQ. At the time, I spoke with Ashley Malin, who’s an outside researcher. She studies toxic exposures at the University of Florida, and she calls it.

ASHLEY MALIN: The most comprehensive and rigorously conducted report of its kind, and so important for our understanding of impacts of fluoride exposure on child IQ.

HUANG: And there were experts, especially within the dental community, that raised concerns about the report immediately. I mean, they were worried that people would misconstrue it to mean that any fluoridation in drinking water is a problem, when the amount of fluoride being discussed was twice what’s added to the public drinking water.

KWONG: OK. And there’s a new turn in this debate. Monday, government researchers published the analysis behind that report in the medical journal JAMA Pediatrics. What did that say?

HUANG: Yeah, yeah. So it gave us some more details about how they’d done their research for this analysis. They had looked at dozens of studies, mostly from China and India, and they used this to conclude that some babies and kids exposed to high levels of fluoride may experience some amount of neurodevelopmental harm. Now, these results are controversial, but the analysis has spurred opponents of fluoridation to call for a new assessment of its benefits and its risks.

KWONG: Today on the show, we weighed into the fluoride debate to separate the science and truth from fear and fiction. You’re listening to Short Wave, the science podcast from NPR.

KWONG: All right, Pien, I think– oh, where to begin. We don’t have time for a complete, exhaustive history of fluoride in drinking water, but what are the major beats? How did this all start?

HUANG: OK. OK, so the story starts, um, at the turn of the 20th century, early 1900s, when dentists in the US started noticing that people who live in certain areas have lower rates of tooth decay, and they don’t know why until a few decades later. The 1930s, when they realized that, in these areas, there’s actually a higher than normal amount of fluoride in the water.

KWONG: Oh, like naturally?

HUANG: Yeah, naturally. And it’s also in the 1930s that a team of scientists at the University of Pittsburgh propose in a paper to add a controlled amount of fluoride to the drinking water to prevent tooth decay.

KWONG: OK, so that is the genesis of this idea.

HUANG: Right, yeah. And then in the 1940s, cities start experimenting with adding fluoride to the water. So it starts with Grand Rapids, Michigan, in 1945. By the end of the decade, dental examiners are reporting markedly lower cavities. And so hearing this, you know, other towns in Michigan, Texas, and Wisconsin start their own programs. And that doubles the number of Americans who get fluoridated water to over a million.

KWONG: Wow, OK.

HUANG: So if you fast forward to 1962, federal drinking water standards are updated to give fluoride guidelines. And then over the subsequent decades, more and more Americans gets access to fluoridated water to protect against tooth decay. That figure is up to around 70% in the US today.

KWONG: And there’s even more fluoride that abounds. There’s fluoride in toothpaste.

HUANG: Yeah, it’s been the case for decades now. I mean, basically every toothpaste I’ve used throughout my entire life has had it in it. Plus, it’s in mouth rinses. It’s in dental floss.

KWONG: It also naturally occurs in all kinds of foods, like spinach, and seafood, and tea, and fruit. You’ll find fluoride there.

HUANG: The science is clear, Emily. Fluoridating water lowers the numbers of cavities in people, which it does by restoring minerals to teeth that are lost when bacteria grow inside the mouth, especially after, like, say, drinking sugary drinks. And this is especially useful for lower-income families who might not have access to fluoride products like toothpaste and mouth rinses. There’s a study by the Colorado School of Public Health which found that adding fluoride to the water saved around $6.8 billion in dental expenses in one year alone.

KWONG: So this has been the story of fluoride for most of our lifetimes. It’s a very rosy public health story, but it sounds like there’s always been a little bit of pushback. Tell me about that.

HUANG: Yeah, so ever since it started, there’s been this debate over fluoridating water. Our colleague Geoff Brumfiel and Selena Simmons-Duffin have reported about conspiracy theories surrounding fluoride in drinking water. There was this time in the 1960s when the John Birch Society, this far-right group, alleged that it was part of a Communist plot. And there are lots of other theories around it as well– different versions that reflected the concerns of their times. But Meanwhile, the scientific understanding is also evolving, which brings us to this latest research in JAMA Pediatrics. It was done by government scientists at the National Toxicology Program.

KWONG: That’s the part of the NIH that you mentioned earlier.

HUANG: With that August report. That’s the one. And like we were saying, they just published a study in JAMA Pediatrics that looks at a few dozen studies that other people have conducted, and it finds this link between high levels of fluoride and a small decrease in children’s IQ. Now, it’s not totally definitive. This is something that they’re saying with moderate confidence.

KWONG: OK, we could have a whole aside about IQ tests and what they measure.

HUANG: Yeah.

KWONG: Sticking with the study, what does moderate confidence mean?

HUANG: So moderate confidence is basically like a grade that they put on the quality of evidence that’s them. It’s not low-quality. It’s not high-quality. It’s enough to say something with moderate confidence. Does that make sense?

KWONG: Yeah, OK. Moderate confidence that high levels again– much higher than what’s added to our drinking water– is associated with a small decrease in IQ.

HUANG: Yeah, could be associated.

KWONG: Could be associated.

HUANG: Yeah.

KWONG: Science.

HUANG: So many words. Yeah. And while this conclusion is not new, this research has already been quite influential in the debate over fluoride in drinking water. It was accompanied by two op-eds in the paper that was published on Monday. One questioned its methods, disagreed with its conclusions, and the other fully supported it. I spoke with Dr. Bruce Lanphear. He’s at Simon Fraser University, and he co-authored that supportive piece.

BRUCE LANPHEAR: The people who are proposing fluoridation need to now prove it’s safe. That’s what this study does. It shifts the burden of proof– or it should.

HUANG: So he’s arguing that there’s enough evidence to prompt this reassessment of the risks and the benefits of fluoride in the water system. Now, on the other hand, you’ve got a dentist like Steven Levy. He’s a public health dentist at the University of Iowa. He wrote the other op-ed that argues for staying the course. And he says that using this data for that debate is a stretch.

STEVEN LEVY: The major problem is that the science is not as strong as it is presented by these authors.

HUANG: So he says that they didn’t fully consider some other recent research that casts doubt on the links between fluoride exposure and IQ. And he also makes the point that, because water fluoridation is so common, we take its benefits for granted. There are problems definitely associated with getting cavities too. It can be painful. You can get infections. You can have to go to the dentist and get expensive fillings, or you can miss school for it. Like, there are all these problems that are also associated with getting cavities.

KWONG: Yeah, I can see why there’s so much pushback, certainly among dentists. But among fluoride’s critics, what are their main questions?

HUANG: Yeah, so there are a couple that are being raised right now. One of them is about whether– you know, because people get fluoride not just from their drinking water, but also from the food that they eat, the toothpaste and mouthwash that they use– whether that total cumulative fluoride might be pushing, you know, some vulnerable people– again, that’s pregnant people and young children– whether that’s pushing their fluoride levels to– levels that might be harmful. And another question is really on the benefit side of it. There is recent analysis that showed that fluoride in the drinking water definitely prevents cavities, but it’s not to the same extent that it was back in the ’40s. ’50s, ’60s before fluoridated toothpaste became a regular thing. So some are saying that it’s time to reweigh the risks and the benefits, given how society has changed.

KWONG: As a science reporter, what do you make of these questions and that they’re being raised right now?

HUANG: I think they’re interesting. I think that, like, it’s useful to have a real scientific debate about these questions. You know, as a science reporter, you’re like, OK, great. These are the questions. Let’s get more evidence. But my concern is that even in the lack of evidence, you know, there’s this huge public debate that’s swirling, and political and sort of happening regardless of whether the evidence becomes clear or not.

KWONG: Right. Science will always move slower than politics. OK, so where does that leave us? Like, what are you watching for next?

HUANG: Yeah, so there’s a couple of things that are coming up. The Environmental Protection Agency has this deadline coming up in the next two weeks over whether they want to appeal this recent court decision that told them to tighten their fluoride regulations. That could have bearing on the debate. And then there’s Robert F. Kennedy Jr. He’s President-elect Donald Trump’s nominee for Health Secretary, and he told NPR that one of his priorities is to get the country to stop fluoridating the water. So we’ll have to see what happens there. And finally, there’s also what’s happening on the local level. So there are some communities that are going through transitions with their drinking water. For example, NPR has reported that Calgary, in Canada, removed fluoride from its water supply. And then, after data came back showing that dental cavities rose significantly, they’re now reintroducing it.

KWONG: OK.

HUANG: On the other hand, you’ve got Florida’s Surgeon General, Joseph Ladapo, who made headlines recently for advising local governments in Florida to stop adding fluoride to their water supplies. So yeah, there’s a lot happening with fluoride right now. It’s going to be interesting to track those decisions and what the public health outcomes are. So we will see what happens.

KWONG: Pien Huang, thank you for summarizing what is a sprawling and complicated conversation right now. I admire it, and I appreciate it.

HUANG: You’re welcome. Thanks for having me on, and I’m sure we’re going to talk much more about fluoride in the future.

KWONG: We recently had Pien on our show as part of a big roundup of health stories from 2024 that will flow over into 2025. You can check out that episode at the link in our notes. We’ll be tracking developments in drinking water, bird flu, and more. If you like this episode, follow us. Whichever podcast app you’re using, click follow right now, and you can stay up to date with all the latest science news. This episode was produced by Hannah Chinn. It was edited by our showrunner Rebecca Ramirez. Rebecca, Pien, and Tyler Jones check the facts. Kwesi Lee was the audio engineer. Beth Donovan is our senior director, and Collin Campbell is our senior vice president of podcasting strategy. I’m Emily Kwong. Thank you for listening to Short Wave from NPR.