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Brian Lehrer: It's The Brian Lehrer Show on WNYC. Good morning again, everyone. Now, we turn to our Health and Climate Story of the Week as we're continuing to do on Tuesdays to make sure these issues don't get buried in the avalanche of other Trump administration news. This week, the recent statement by Health and Human Services Secretary Robert F. Kennedy, Jr., that he is working to "change the federal fluoride regulations to change the recommendations."

He praised Utah for becoming the first state to prohibit local governments from adding fluoride to its water supply and believes that all public water systems should follow suit. Fluoride has been in use in the United States since 1945. Since then, it has drastically reduced dental cavities and improved oral health in adults and kids alike. The Centers for Disease Control considers water fluoridation one of the greatest public health achievements of the 20th century. At the same time, late last year, 2024, the National Toxicology Program released a systematic review of the published scientific literature.

That review found that very high levels of fluoride exposure, to be clear, far more than what's in the current water supply in the United States, was associated with lower IQs in children. Now, some public health experts are concerned that some pregnant people and babies might be getting more fluoride than they need or should have, especially when combined with fluoride from other sources like toothpaste, mouthwash, and water-based food and beverages. The question now for the scientific community is far more nuanced than Kennedy's take. Does the current level of fluoridation need to come down a bit? If not, are there certain populations that should try to avoid fluoridated water for a period of time?

Joining us now to compare notes on what the science says about water fluoridation are two experts, Jessica Steier, doctor of public health, CEO of the group Unbiased Science and host of the Unbiased Science podcast, and Linda Birnbaum, scientist emeritus and former director of the National Institute for Environmental Health Sciences, as well as the National Toxicology Program and scholar in residence at the Nicholas School of the Environment at Duke University. Dr. Steier and Dr. Birnbaum, thanks so much for joining us. Welcome to WNYC.

Dr. Jessica Steier: Thanks so much for having me and for having this really important conversation.

Dr. Linda Birnbaum: It's a pleasure to be here.

Brian Lehrer: Dr. Steier, let me begin with you and just invite you to do a bit of fluoride 101. I see around 63% of the US population gets fluoridated water in their local water system. One might have assumed it was around 100% of the US population. Why is it in some water supplies and not and how is it added?

Dr. Steier: Great, great question. Fluoride is a naturally occurring mineral. It's in our Earth's crust. Things that are grown in the earth or water supply, there are some areas that just have naturally occurring levels of fluoride that are higher than in other areas. Then as you noted, and I love the nuance and how you keyed up the conversation, about 80 or so years ago, we started adding fluoride to the water supply in areas that have low levels of naturally occurring fluoride in water, because we noticed that in areas that had higher levels of fluoride, dental outcomes were better. I'll pause there, but this is something that's been around for about 80 or so years. As you said, it's been lauded as one of the top public health achievements of our lifetime.

Brian Lehrer: All right. Dr. Birnbaum, since you've been with the National Toxicology Program, can I get you to explain in more detail this review of the scientific literature that they released last year that found that very high levels of fluoride exposure, far more than what's in the current water supply in the United States, again, to be clear, that these certain levels were associated with lower IQ in children?

Dr. Birnbaum: Sure, but I think it's important to realize that I retired five and a half years ago. The NTP's review of fluoride developmental neurotoxicity actually started in around 2015 and 2016, in part driven by conclusions of the National Academies of Science that there was some concern that fluoride could impact the developing brain. The question that the NTP scientists were asking was, is fluoride developmentally neurotoxic or does it have the potential to do that?

After extensive review of-- there's something like 74 studies that have been published. Now, many of them are in China, but there are 10 or 11 high-quality, low-biased studies. Many of them, or some of them at least, are what we call "longitudinal perspective," which means you have measurements of what exposure is long before you look for what the effects are, not at the same time. Many of those studies, the majority, show an association between impacts on IQ in children and the exposure early in life.

Brian Lehrer: Can I get your take on the way Kennedy referenced that study saying, "The more you get, the stupider you are"?

Dr. Birnbaum: Well, I think that's kind of a simplification. We do know that at high levels, I think there's no question that there are impacts on the developing brain. We know that the brain develops most before the baby's even born, in utero and early life. Those are the windows of exposure when we have the most concern. I want to take issue a little bit with the comment that the levels where these effects are definitely documented are very high.

They're approximately two times the recommended level of intentional water fluoridation. The newest studies, and there are three of them, clearly show that there's no evidence of a threshold for the effects on the developing brain. There's actually a study that just came out two months ago, a high-quality study that shows that effects at the current levels of exposure in the US. This was not a US study. I have to say that.

This was done in Bangladesh with Swedish investigators. The data was clear that at levels of urinary fluoride-- and that is an individual measure of what exposure was. It accounts for all sources of exposure, not just drinking water, what fluoride is in the drinking water. In that study, it was clear that there were impacts on IQ at levels that are in the current population.

Most of the work was not geared to asking the question is 0.7 parts per million, which is the current recommended level. I should say, I was on the committee of the public health service that recommended that level, which was largely based on the prevalence of dental fluorosis, which is mottling and spots on the teeth. At that level, there was not so much of that.

Although I should say that today, well over half of all children and adolescents do have some dental fluorosis. At that level, the 0.7, there are effects that are beginning to be studied. I do not disagree that we need more study. Scientists always call for more research. As a public health scientist, I think we know enough now to say that we have concerns about the developing fetus and infants and their exposure to flooring in the water supply.

Brian Lehrer: Dr. Steier, your response to any of that?

Dr. Steier: Yes, and thank you, Dr. Birnbaum, and thank you for all the work that you've done. Just to comment on the NTP report, just for starters, it was not intended to speak to water fluoridation programs. As you both noted, they were studying levels that are more than double what we're talking about in the community water fluoridation programs. They were looking at exposures at 1.5 milligrams per liter or higher where, in the US, our water fluoridation is set at 0.7, as Dr. Birnbaum noted.

A few things. Most of the studies included were outside the US. We're talking about naturally occurring fluoride levels, again, more than double than what's in our community water fluoridation programs. The review did not consider at all any of fluoride's dental health benefits. There was no risk-benefit analysis. There are also a lot of issues with, first of all, the way that we measure IQ, especially in young children.

When you take a close look at what they found, they were looking at differences of only a couple of IQ points. I'm not a clinician, but I know there's been debate over whether that's even clinically relevant. The other thing I'll say is that some of the recent studies that have come out have relied on things like urine spot checks. Some scientists have raised issues with the way that we're measuring fluoride in urine and that there are different factors that can impact the concentration of fluoride that's detected in our urine.

There's also the possibility that we're introducing error, given the short half-life of fluoride, how much water a person has consumed. There are different factors that basically call into question the way that we're actually measuring fluoride in urine. Also, there's been a lot of criticism overall of the studies that have been done investigating this topic, some significant methodological flaws.

That's led to major organizations like the American Academy of Pediatric Dentistry, American Academy of Pediatrics, and many others to reassert their support for community water fluoridation. We could certainly talk more about that, but it's a safety net for so many people who either don't have access to or not regularly brushing their teeth with fluoridated toothpaste or mouthwash. There's also a different mechanism of action between topical and systemic fluoride, which I'm happy to talk about as well.

Brian Lehrer: Can I ask you this as a follow-up, Dr. Steier? If I understood Dr. Birnbaum correctly, there's even some evidence that at the current recommended level of fluoride in the water supply, not only at the greater levels that were looked at in the toxicology program review, that there is some evidence of some neurological impact on children. If I understood that correctly and, Dr. Birnbaum, correct me if I'm wrong. Dr. Steier, what about that?

Dr. Steier: I have not seen compelling evidence. It's very possible that I haven't seen it. I'd love to read those studies. I know that there was one big study that came out of Canada. I don't know if that's what we're referencing in 2019. I believe it was the MIREC study, Maternal-Infant Research on Environmental Chemicals. That's a study that's often cited. The primary outcome was supposed to show whether there are differences in IQ resulting from fluoride exposure.

What they found, if you actually look at the details, they found that the scores were nearly identical in terms of IQ, although that was not highlighted. There were also some major methodological studies that have been pointed out in follow-up research. Many studies on this topic have actually been retracted due to serious concerns about methods used. Again, it's possible that something came out that I just have not read.

Brian Lehrer: Dr. Birnbaum?

Dr. Birnbaum: Yes. Well, first of all, I think there have been quite a number of studies since the 2019 study, including the one that I just cited from just two months ago that was published in Environmental Health Perspectives. There have been quite a number of studies. I don't know of many studies that have been retracted for methodological. I think the methods that have been used, the epidemiological methods of environmental epidemiology, have been solid.

I assume or I certainly hope, Dr. Steier, that you have read the JAMA Pediatrics meta-analysis that was published on January 6th, which I think does demonstrate through multiple different kinds of modeling, the evidence for effects below or in the range of 0.7 and no evidence for a threshold. I did want to address to go back to something you said a little bit before about what does a 2 or 3-point IQ deficit mean, and for an individual that's very hard to detect.

In other words, Brian, if you had three or four points, if you had a little less blood lead as a kid, you might have lower IQ. We could never pick that out. On a population base, when you shift the distribution of a population by two or three points, that has tremendous educational and economic consequences going forward. I think that's something that we need to think about that it may be hard to see impacts in individuals, but this is a population-based impact.

Dr. Steier: If I could just comment on that. I think that certainly, as a public health scientist, I'm definitely focused on population health. I know when I look at the public health data, we know, speaking of population health benefits, that every $1 invested, of course, in water fluoridation is estimated to save about $38 in dental treatment costs. Communities that use fluoridated water save an average of about $32 per person per year by avoiding treatment for cavities.

We also have real-world evidence. We've compared municipalities that have removed. I think it was Calgary that ceased water fluoridation in 2011. We're talking about Canada now. Compared to Edmonton, which maintained it, they found significantly higher caries prevalent in Calgary's children. This was so compelling that Calgary is now planning to resume water fluoridation.

In the US, we saw this similarly in Juneau, Alaska, after they stopped water fluoridation in 2007. They found that children had significantly more dental caries-related procedures. Actually, there was a health bulletin that noted that childhood cavity rates doubled in Juneau. I'll just reassert here that I have not seen compelling data using validated methodology that has shown a significant impact clinically relevant on children's IQ.

If that were to be the case, it would certainly call into question, although I would hope that that would be balanced against the very well-established benefits of community water fluoridation with regard to oral health, especially at a time when we know, was it just last month if I'm not mistaken, the CDC's Division of Oral Health was eliminated. We're seeing further cuts to Medicaid programs. We know that access to dental care, oral care is a major, major issue. Community water fluoridation has been a way to protect children regardless of their economic status.

Brian Lehrer: Listener writes-- Oh, go ahead briefly, Dr. Birnbaum.

Dr. Birnbaum: Yes, I want to make one comment. I'm not sure, or at least I am, the most recent Cochrane reviews of the benefits of community water fluoridation. This was published in November of '24. The Cochrane reviews are the best evidence-based reviews that are done, show a very small, if any, benefit in community water fluoridation today as far as protection against cavities.

If you look at the data from countries that have intentional fluoridation versus countries that don't have fluoridation and use ones that have similar socioeconomic characteristics, what you find is while there were big differences in the 1960s and the 1970s, today, there are essentially no differences at all. The evidence today that community water fluoridation, when there are so many other sources of fluoride, and I do want to go back to the point--

Brian Lehrer: Just a quick follow-up on that.

Dr. Birnbaum: Sure.

Brian Lehrer: Do we not have higher rates of dental cavities in lower-income populations in the United States, I think Dr. Steier was just referencing that, than in other populations, especially with less access to dental care economically? Go ahead.

Dr. Birnbaum: That is an issue that is always brought up, and we don't have good data to support it. In the Cochrane review, they said at this point, there wasn't good data to either support that or refute that point. It's certainly something that needs to be looked at.

Brian Lehrer: When you refer to other countries, we have a listener text that says, "In Europe, only about 2% of the population has fluoridated water." Is that your understanding, Dr. Birnbaum?

Dr. Birnbaum: That is correct.

Dr. Steier: However, they do have other sources of fluoride like fluoridated milk. They also have school fluoridation programs. They fluoridate salt. I've heard that cited many times, but I think it overlooks the fact that they are getting fluoride from other sources. Again, that's systemic.

Dr. Birnbaum: Dr. Steier, I totally agree with you. That's the point. We in this country are overlooking all the other sources of fluoride that people are getting as well. In fact, fluoridated toothpaste was one of the major advances and has had a major impact in terms of caries prevention.

Brian Lehrer: Dr. Steier, listener writes, "Please cover the chemical industry's interest in water fluoridation." Are fluoride producers, if there is such an industry, making a bundle on this and that plays into the conversation, unfortunately, Dr. Steier, in your opinion?

Dr. Steier: It's a great question. I'm not aware of big fluoride. I'm just a lowly public health scientist, so I couldn't weigh in on that. Can I comment on one other thing, if I may, just about the other sources of fluoride? That's a really, really great question. As far as I understand, fluoride was only added to the National Health and Nutrition Examination Survey. We call it NHANES in 2022. We have limited nationally representative data on fluoride levels in Americans. Preliminary data does not indicate excessive fluoride excretion.

Then there was a study that was published. I think it was just a couple of months ago. Yes, it was in February of 2025 that showed that fluoride bioaccessibility from foods and beverages averages only about 45%. What this means is that theoretical concerns about excessive fluoride may actually be overestimated since we're not absorbing all consumed fluoride. Hence, why we excrete it in our urine.

One other point that I'd be remiss if I didn't comment on is that topical versus systemic fluoridation, they work in different ways, right? They're dual pathways. When fluoride is consumed in water, it not only contacts teeth directly, but it enters our body's water pool, and then it reemerges in our saliva. What it does is it provides this continuous low level of protection throughout the day, whereas topical applications like toothpaste, yes, it's true that they provide higher concentrations of fluoride, but they're really only helpful right after we're applying them, right? They're not going to help us throughout the day every time we eat a meal or drink something.

Brian Lehrer: We just have a minute left in this segment. I want to ask after this nuanced conversation between the two of you public health experts, how do you recommend we go forward on a policy level if RFK Jr. is not nuanced and is just saying wipe it all out of the water supply? Dr. Birnbaum, you quickly 30 seconds, and then Dr. Steier, 30 seconds, and then we're out.

Dr. Birnbaum: I support the recommendations of the ADA, the American Dental Association, and the American Academy of Pediatrics that pregnant women should not take supplemental fluoride and infants should not. You should not make formula, for example, with fluoridated water.

Brian Lehrer: Dr. Steier?

Dr. Steier: That's actually not the recommendation. It is safe to use fluoridated water to mix formula if your baby's younger than six months old. I would say that it's disastrous. This is a disastrous recommendation that will set us back decades and we're going to see this. Unfortunately, public health is a victim of its own success. If we do, in fact, remove fluoride from the water supply, I think we're going to be paying for it big time.

Brian Lehrer: Jessica Steier, DrPH--

Dr. Birnbaum: I would remind everyone--

Brian Lehrer: You want to get the last look at that?

Dr. Birnbaum: Yes, I would remind people that the secretary does not have regular authority over fluoride in drinking water. That is the responsibility-

Brian Lehrer: It's the EPA, isn't it?

Dr. Birnbaum: -of the EPA. The EPA's current level would suggest that the margin of safety should have levels in water of 0.4 ppm, which is essentially half of what it is.

Brian Lehrer: Jessica Steier, DrPH, that's Doctor of Public Health, CEO of the group Unbiased Science and host of the Unbiased Science podcast. Linda Birnbaum, scientist emeritus and former director of the National Institute for Environmental Health Sciences, as well as the National Toxicology Program, and a scholar in residence at the School of the Environment at Duke University. Thank you both very much for joining us.

Dr. Steier: Thanks so much.

Dr. Birnbaum: Thank you.

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