Wellness, Actually · August 13, 2026
Is fluoride in drinking water safe, and does it still work?
Short answer
At the levels used in US water, about 0.7 parts per million, fluoride looks safe and still useful. The IQ findings people cite come mostly from rural China and India where natural groundwater fluoride runs many times higher and often carries arsenic and lead with it; a 2023 meta-analysis that split studies by dose found no IQ association at low levels. Meanwhile towns that stopped fluoridating, including Calgary in 2011 and Israel in 2014, saw cavities and dental visits rise.
For something as unglamorous as a municipal water supply, fluoride generates a remarkable amount of rage. Two states, Florida and Utah, banned community fluoridation outright in 2025, and the argument driving that is not about teeth. It's about whether we are quietly lowering our children's IQ.
So let's take both halves seriously: does fluoridated water still do anything for teeth, and is there a real neurodevelopmental signal at the doses Americans actually drink?
Why fluoride ended up in the water in the first place
The story starts in 1901 with Frederick McKay and a condition called Colorado brown stain, seen in and around Colorado Springs. People there had ugly brown mottling on their teeth. They also had strikingly few cavities. It took until 1931 for H.V. Churchill at Alcoa to run spectrographic analysis on the water and find the culprit: naturally occurring fluoride, around 13.2 parts per million in the affected areas.
That number matters, because almost every fight about fluoride is a fight about dose. Roughly 10 ppm is where you get brown staining. Three to four ppm gives you white-spotted fluorosis. The target in fluoridated American water is 0.7 ppm, about a tenth of the Colorado brown stain level. The dose-finding work in 1941 and 1942 established that low doses protect teeth without staining them. In 1945 Grand Rapids, Michigan became the first community to fluoridate, at 1 ppm. Nearby Muskegon served as the control. Over the next 15 years, cavities in Grand Rapids fell by about 50%.
The reason we knew where to look at all is that fluoride varies naturally across geography. Parts of China and India have very high groundwater fluoride. Colorado Springs did too. That natural experiment is what produced the dosing curve.
The US Public Health Service endorsed fluoridation in 1950. Crest launched the first fluoride toothpaste in 1955, and by 1975 fluoride toothpaste was everywhere. Then, in 2024, a federal court found an "unreasonable risk" from fluoridation under the Toxic Substances Control Act and ordered EPA action. A higher court vacated that ruling. Florida and Utah passed their bans anyway.
The chemistry is not in dispute
Tooth enamel is built from a crystal called hydroxyapatite. Fluoride slots into that crystal through ordinary chemistry and turns it into fluoroapatite, which is denser and less soluble. The part that actually matters for cavities is acid resistance. Bacteria in your mouth make acid after you eat, dropping oral pH to around 5. Hydroxyapatite starts dissolving around pH 5.5. Fluoroapatite holds until about 4.5. That is one pH unit, and pH is a log scale, so it's a tenfold difference in acid concentration. There's also some evidence fluoride has antibacterial properties.
Fluoride protects teeth. We know the mechanism, and randomized trials of fluoride toothpaste and varnishes show they reduce cavities. So that isn't the live question.
Do we still need it in the water now that everyone has toothpaste?
This is the strongest skeptical argument, and it deserves a real answer. Dumping fluoride into a reservoir is effective but coarse. If toothpaste has made it redundant, stop.
The evidence here is genuinely weaker than it was in 1945. A 2018 paper in the Journal of Dental Research used NHANES to compare kids in high-fluoridation counties with those in low-fluoridation counties and found about 30% fewer cavities in the high group. But those counties differ enormously in rural versus urban makeup, income, and plenty of other things that also drive cavities. Residual confounding, again.
Anti-fluoride groups lean hard on the Cochrane review, which is cited as showing no meaningful effect of fluoridation on cavities after 1975. Cochrane is the gold standard in meta-analysis, so this sounds decisive. Read the data, though. The review examined the initiation of fluoridation in a water supply, and very few places both started fluoridating after 1975 and studied it in publishable form. Only two studies met the criteria. The confidence intervals are enormous. That is an absence of evidence, not evidence of absence, and the nuance does not survive the trip to Instagram.
The more useful modern evidence comes from places that turned it off. Calgary stopped fluoridating in 2011, and compared with Edmonton, which kept going, cavities rose. Not catastrophically, but they rose. Similar patterns showed up in Alaska. Israel banned community fluoridation in 2014 and saw roughly a doubling of child dental visits on time trend analysis. You can quibble with time trends, but this is stronger than comparing fluoridated and unfluoridated counties, and it answers the actual policy question, which is what happens if your town stops.
There's a second point that gets too little airtime. Dental coverage in the US is bad even at the best of times, and many people effectively have none. My kids would be fine if fluoridation ended tomorrow. They have fluoride toothpaste, they go to the dentist twice a year, they get varnishes, and a cavity would be caught and filled fast. That is not every kid's situation. Hyperindividualism in health policy leaves behind the people with the fewest other resources, and dental health tracks parental income and education tightly. Fluoride in the water is a safety net.
Is a cavity really so bad? There are correlations between dental problems and poor academic performance and school absenteeism, though nobody randomizes children to cavities, and those correlations plausibly reflect who has access to dental care rather than cavities lowering test scores.
The IQ studies, taken seriously
Nobody is out there advocating for cavities. The fight is about the brain.
Start with what gets called the "Harvard study," a 2012 meta-analysis in Environmental Health Perspectives covering 27 studies of fluoride exposure and children's IQ. The headline finding: high-exposure kids scored about seven IQ points lower than low-exposure kids. (An aside from a Yale guy: an author working at Harvard does not make it a Harvard study. When I publish something it isn't the Yale study. It's my study.)
The critical detail is where those studies came from. Most were conducted in rural China, in areas where the groundwater fluoride is naturally very high, not places adding it. The same bedrock is frequently loaded with arsenic and lead, partly through industrial runoff, and some of these regions have iodine deficiency. So the question that meta-analysis answers is what happens to IQ when you raise fluoride from an already high level to a higher one. That is not the question anyone in the US is asking. These are ecological studies: an estimate of area exposure correlated with an estimate of area IQ. Low-quality evidence by design.
Some studies try to measure exposure directly with urinary fluoride, which sounds more rigorous. The MIREC study in JAMA Pediatrics in 2019 followed 601 mother-child pairs across six Canadian cities and reported that each additional 1 mg/L of maternal urinary fluoride was associated with 4.5 fewer IQ points in boys, with no association in girls. That paper has problems in the plural, not the singular. Exposures were mostly low, with a few high-exposure areas apparently driving the results. The estimates shift a lot with adjustment for family differences, which suggests something else is going on. And there is no reason to expect an effect in boys only, which smells like subgroup fishing. It's also a few hundred subjects.
Since I'm a nephrologist, one more thing about urinary fluoride. Urine concentration ranges from roughly 100 to 1,000 mOsm/L, a tenfold spread, so any urinary measurement needs correcting for that. Studies typically adjust with specific gravity, which is a poor concentration marker, or osmolarity, which is better. At least they think about it. What nobody adjusts for is urinary pH, and fluoride excretion is pH dependent. In acidic urine, about 95% of filtered fluoride is reabsorbed before it leaves your body. In alkaline urine, only about 45% is. That is a dramatic difference, and urinary pH is influenced by diet and when you last ate. I have never seen a paper account for it. A fancier-sounding measurement is not automatically a less biased one.
The study that organizes this literature best is a 2023 meta-analysis that did something simple: split the water-fluoride studies into high-baseline areas, mostly China and India, and low-baseline areas, many in Canada and Mexico. In the high-fluoride areas, adding more fluoride looked bad for IQ. At low levels, variation in fluoride showed no relationship to IQ. That is precisely the pattern you'd expect from a substance that is harmful at high doses and not at low ones.
The Broadbent study in the American Journal of Public Health is worth knowing about because it avoids the cross-sectional trap. Every person born in Dunedin, New Zealand between April 1972 and March 1973 was enrolled and followed for 38 years, with prospective fluoride exposure measurement and repeated IQ testing. No differences by fluoride exposure.
How often does US water actually run high? CDC monitoring from roughly 2016 to 2021 looked at how often levels exceeded 2 mg/L, which is genuinely high enough that you'd want to bring it down. It happened in 0.01% of cases. And exceedances get corrected, because that is what monitoring a water system is for. If anything, the CDC found more systematic error in the other direction, water fluoridated below target.
I'll go further than the dose-response framing. I'm not convinced high fluoride lowers IQ either. I don't have a plausible mechanism, and if your groundwater fluoride is spiking because you live next to an industrial runoff site, the confounding is severe.
If you care about your child's IQ, fluoride is a strange lever to pull
There is a lot of high-quality, often randomized evidence on moving children's cognitive development. Micronutrient supplementation in low-resource settings, iodine repletion in people who are truly deficient, early childhood education, preschool access, Head Start, support for parents. Reading to kids improves IQ, and that is well documented. Dolly Parton mails free books to children, which puts her ahead of any plausible fluoride effect by an enormous margin.
Removing fluoride from the water has one advantage those interventions lack: it doesn't require a line in a budget. It's free to the government, which is not the same as free.
While we're here, the pineal gland claim. The pineal gland secretes melatonin, and it does calcify with age; autopsy studies find calcification in about 60% of people, and it can contribute to sleep trouble later in life. The crystal that forms there is hydroxyapatite, the same mineral as in enamel, and fluoride binds hydroxyapatite. So if you look for fluoride in a calcified pineal gland you will find some, for the same reason you find it anywhere hydroxyapatite exists. There is no evidence fluoride accelerates the calcification, and I could not locate a single study, in any journal of any quality, on fluoride and psychic ability.
Bottom line
Fluoride protects teeth through a well-described mechanism, and the modern evidence for community water fluoridation comes mostly from places that stopped, where cavities went up. The neurodevelopmental studies that frighten people are drawn largely from regions with endemically high natural fluoride, frequently alongside arsenic and lead, and when you split the literature by dose the association disappears at the levels Americans drink. Quoting the high-dose finding does not make it true at 0.7 ppm.
None of which means those researchers are frauds or that the question was silly to ask. But we systematically accept weaker studies when the proposed harm is upsetting, and "this might damage your child's brain" is about as upsetting as it gets. Fear is more salient than reassurance, and neither the risk nor the benefit here is visible to any individual parent. A one-point IQ shift is undetectable in one child. So is the cavity your kid would not have gotten. You shouldn't run your life on poor-quality studies, and you should be glad we treat our water at all, because cholera and dysentery are still killing children in places that can't.
Here's our discussion from the episode:
I covered this in depth on Wellness, Actually, listen below.
Frequently asked questions
How much fluoride is in US tap water?
The target for community water fluoridation in the US is 0.7 parts per million. For comparison, the naturally high-fluoride water in Colorado Springs that caused brown tooth staining ran around 13.2 ppm, and white-spotted fluorosis appears around 3 to 4 ppm. CDC monitoring from about 2016 to 2021 found levels above 2 mg/L in only 0.01% of cases, and those exceedances get corrected.
Does fluoride in water lower children's IQ?
Not at the levels used in the US, based on the best available evidence. The studies reporting IQ effects, including the 2012 meta-analysis often called the Harvard study, come mostly from rural China where natural groundwater fluoride is very high and often accompanied by arsenic, lead, and iodine deficiency. A 2023 meta-analysis that split studies by baseline fluoride level found an association in high-fluoride areas but none at low levels, and the Broadbent cohort in Dunedin, New Zealand followed people for 38 years with repeated IQ testing and found no differences.
How does fluoride actually prevent cavities?
Tooth enamel is made of a crystal called hydroxyapatite. Fluoride incorporates into that crystal to form fluoroapatite, which is denser and less soluble. Hydroxyapatite begins dissolving around pH 5.5 while fluoroapatite holds until about 4.5, and because pH is a log scale that one unit is a tenfold difference in acid concentration. Mouth bacteria drop oral pH to roughly 5 after you eat, which is why that gap matters.
Do we still need fluoride in water now that everyone uses fluoride toothpaste?
The evidence is weaker than it was in 1945 but still points toward yes. Calgary stopped fluoridating in 2011 and cavities rose compared with Edmonton, similar patterns appeared in Alaska, and Israel saw roughly a doubling of child dental visits after banning fluoridation in 2014. Water fluoridation also functions as a safety net for children without reliable dental coverage, since dental health in the US tracks closely with parental income and education.
What does the Cochrane review say about water fluoridation?
It is widely cited as showing no meaningful effect on cavities after 1975, but the review examined the initiation of fluoridation in a water supply, and only two qualifying studies started after 1975. The confidence intervals are very wide. That is an absence of evidence rather than evidence that fluoridation stopped working.
Does fluoride calcify your pineal gland?
There is no evidence fluoride accelerates pineal calcification. The pineal gland does calcify with age, with autopsy studies finding it in about 60% of people, and it can contribute to sleep difficulties later in life. The crystal that forms there is hydroxyapatite, the same mineral as tooth enamel, and since fluoride binds hydroxyapatite you will find fluoride there if you look, just as you would anywhere hydroxyapatite exists.
Wellness, Actually Podcast
"What's the deal with fluoride?" — Listen to the full episode, including the week's health news and listener Q&A.
About the author
F. Perry Wilson, MD MSCE is a nephrologist, clinical researcher, and Associate Professor of Medicine and Public Health at Yale University, where he directs the Clinical and Translational Research Accelerator. He hosts the Wellness, Actually podcast with Emily Oster, writes the weekly Impact Factor column on Medscape, and is the author of How Medicine Works and When It Doesn't (Grand Central, 2023).