Fluoride in Water — Is It Safe? What the 2024 NTP Report Changed

Water fluoridation — deliberately adjusting the fluoride level in public water systems to a level considered optimal for cavity prevention, typically 0.7 mg/L in the United States — has been practiced in the US since the 1940s and is recognized by the Centers for Disease Control and Prevention as one of the ten greatest public health achievements of the 20th century, alongside vaccination and infectious disease control. Decades of epidemiological data show a real, measurable reduction in cavity rates in populations using fluoridated water compared with populations without this intervention.

In August 2024, things got more complicated. The US National Toxicology Program (NTP), a government agency known for rigorous, multi-year toxicological reviews, published a long-awaited monograph (NTP Monograph 08) on fluoride and neurodevelopment, which, with moderate confidence, links higher fluoride exposure levels to lower IQ in children. A month later, a federal court in California ordered the US Environmental Protection Agency (EPA) to begin a regulatory process concerning water fluoridation under the TSCA law. Both of these events are real and true — the question this article tries to answer honestly is what they actually mean, and don't mean, for the standard water-fluoridation level.

Fluoride protects teeth from cavities through two complementary mechanisms. The first, now considered dominant, is topical (local) action — fluoride present in saliva and dental-plaque fluid supports remineralization of early, microscopic enamel damage by incorporating into the hydroxyapatite structure and forming more acid-resistant fluorapatite, while also making it harder for cavity-causing bacteria to produce demineralizing acids. This mechanism is behind the effectiveness of fluoride toothpaste, mouth rinses, and fluoride varnish — the action happens directly on the tooth surface, regardless of whether the fluoride comes from water, toothpaste, or another source.

The second mechanism, historically considered the main reason for introducing water fluoridation, is systemic action — fluoride ingested (e.g., in drinking water) during tooth development in children becomes incorporated into enamel structure before the tooth erupts, making it inherently more acid-resistant from the start. Newer research suggests the relative contribution of this systemic mechanism to the total benefit of water fluoridation is smaller than previously thought, compared with the topical mechanism — which matters for assessing whether the same dental benefits could be achieved with lower total systemic exposure, mainly through fluoride toothpaste rather than ingesting fluoride in water.

The decision to fluoridate drinking water in the US in the 1940s and 50s was based on observed natural differences in cavity rates between cities with different naturally occurring groundwater fluoride levels, followed by controlled studies comparing cities before and after fluoridation was introduced. These early studies showed cavity reductions on the order of several dozen percent, which, combined with the intervention's low cost and population-wide reach (reaching everyone using the water supply, regardless of access to dental care), made water fluoridation one of the most cost-effective public health interventions of the 20th century.

Newer systematic reviews, accounting for the fact that fluoride is now widely available from toothpaste (which wasn't common in the 1940s), show a smaller, but still real, additional benefit from water fluoridation alone on top of a population that already has access to fluoride toothpaste — on the order of low double-digit percentage reductions in cavities, not several dozen percent. This is an important caveat: the benefit of water fluoridation hasn't disappeared, but its relative size is smaller in a world where fluoride toothpaste is standard than it was when fluoridation was first introduced.

An independent, not-yet-peer-reviewed (preprint) reanalysis of this meta-analysis by other researchers raised further methodological and statistical objections to the original paper. This is a normal, healthy part of scientific verification — a controversial finding on an important public health topic should go through this kind of critical scrutiny, and the existence of a methodological dispute in the literature doesn't mean the NTP report or the meta-analysis are worthless, only that conclusions at this stage warrant appropriate uncertainty, rather than a final verdict in either direction.

In September 2024, Judge Edward Chen of the US District Court for the Northern District of California (Food & Water Watch and others v. EPA) ruled, after two separate bench trials, that water fluoridation at 0.7 mg/L poses an unreasonable risk of reduced IQ in children under the Toxic Substances Control Act (TSCA), and ordered the EPA to begin a formal regulatory process on the practice. It was a precedent-setting ruling — the first time a court ordered the EPA to begin such a regulatory proceeding in response to a previously denied citizen petition under this law. The court, however, did not specify what specific actions the EPA must take (a ban, a lowered level, or other measures) — that was left to the agency itself.

The case didn't end with that ruling, though. In May 2026, the Ninth Circuit Court of Appeals vacated the district court's order, without ruling on the merits of whether fluoride in drinking water at 0.7 mg/L presents an unreasonable health risk — the appeals court focused on narrower procedural questions about the scope of evidence that can be considered in this type of TSCA proceeding, without issuing a final verdict on the health-risk question itself. In other words, the legal question of whether the EPA must regulate water fluoridation remains open and ongoing, not finally resolved in either direction.

Equally wrong is the opposite oversimplification — claiming the 2024 NTP report and court ruling have no significance at all and that the topic of water fluoridation is fully settled with no new questions. The report comes from a government toxicology agency with an established methodological reputation, and the question of fluoride exposure effects at higher levels — including among people drinking water with naturally high fluoride levels in some regions of the world — is a real, worthwhile public health topic for further research.

This topic can't be honestly summarized in one sentence like "fluoride is safe" or "fluoride is dangerous" — and trying to do so in either direction would flatten a genuinely nuanced scientific picture from 2024 and 2025. Decades of data on dental benefits are real. The NTP report linking higher exposure levels to lower IQ in children is also real, methodologically solid, and published by a credible agency — but it concerns exposure levels significantly higher than standard water fluoridation, not that practice itself.

For most readers in Poland, this dispute matters mainly for general awareness, since the national fluoride-prevention system doesn't rely on water fluoridation. For people living in regions with naturally high groundwater fluoride levels (which occurs in some parts of the world, including regionally in some countries), checking the actual fluoride level in local water is a sensible, concrete step — far more useful than general worry based on headlines alone.