The NTP fluoride monograph: what it found above 1.5 mg/L, and what it did not test at 0.7

What it says#

The National Toxicology Program, part of the National Institute of Environmental Health Sciences at NIH, posted NTP Monograph 08 on August 21, 2024: a systematic review of the human, animal and mechanistic literature on fluoride exposure and neurodevelopment and cognition. The review evaluated children and adults separately. In children it found 72 studies of fluoride exposure and IQ; 19 were rated high quality, and 18 of those 19 reported an inverse association between estimated fluoride exposure and IQ. The 18 include 3 prospective cohort studies and 15 cross-sectional studies from 5 countries. Forty-six of the 53 low-quality studies pointed the same way. Eight of nine high-quality studies of other cognitive or neurodevelopmental outcomes reported associations, but because the outcomes were so varied the monograph gives that body of evidence low confidence.

The headline conclusion is one sentence: the review "finds, with moderate confidence, that higher estimated fluoride exposures (e.g., as in approximations of exposure such as drinking water fluoride concentrations that exceed the World Health Organization Guidelines for Drinking-water Quality of 1.5 mg/L of fluoride) are consistently associated with lower IQ in children." The next sentence is "More studies are needed to fully understand the potential for lower fluoride exposure to affect children's IQ." NTP uses four confidence levels, high, moderate, low and very low; its summary page adds that an association "does not prove a cause and effect."

The monograph's own front matter draws the boundary. Under "What This Monograph Does Not Do" it says the review does "not address whether the sole exposure to fluoride added to drinking water in some countries (i.e., fluoridation, at 0.7 mg/L in the United States and Canada) is associated with a measurable effect on IQ," does not "provide a quantitative estimate of the number of IQ points lost for a given increase in fluoride exposure," and does not "assess benefits of the use of fluorides in oral health or provide a risk/benefit analysis." NTP's summary page puts it more plainly: "there were insufficient data to determine if the low fluoride level of 0.7 mg/L currently recommended for U.S. community water supplies has a negative effect on children's IQ." On adults, the monograph found only two high-quality cross-sectional studies and gives low confidence to any association; the summary page says NTP "found no evidence that fluoride exposure had adverse effects on adult cognition." Animal studies "provide little insight," and human mechanistic studies were too few and too varied to judge biological plausibility.

The introduction explains why 1.5 mg/L is the line. The U.S. Public Health Service first recommended community water fluoridation in 1962; for years most systems ran at 0.8 to 1.2 mg/L, and PHS now recommends 0.7 mg/L. The EPA's enforceable maximum for fluoride in drinking water, set to protect against skeletal fluorosis, is 4.0 mg/L, with a non-enforceable secondary standard of 2.0 mg/L above which public water systems must notify the public. The WHO guideline of 1.5 mg/L, first set in 1984, is meant to protect against dental and skeletal fluorosis. NTP chose it as "a useful total fluoride exposure equivalent metric" because "no alternative safety guidelines for total fluoride exposure exist." The monograph notes that total exposure varies with dental products and beverages such as black tea even where water is at the recommended level. As of April 2020, community water systems with 1.5 mg/L or more of naturally occurring fluoride served about 0.59 percent of the U.S. population, roughly 1.9 million people, and a 2024 estimate the monograph cites puts systems and private wells above 1.5 mg/L at more than 2.9 million residents.

The companion meta-analysis by the same NTP scientists, published in JAMA Pediatrics on January 6, 2025, pooled 74 studies, 22 high quality and 52 low quality, from 10 countries. None was conducted in the United States. NTP's page reports its central estimate, a decrease of 1.63 IQ points for every 1 mg/L increase in urinary fluoride, and says the high-quality studies showed associations below 1.5 mg/L when fluoride was measured in urine or water, with few studies and therefore uncertainty below 1.5 mg/L in water alone, and "not enough data to determine if 0.7 mg/L of fluoride exposure in drinking water affected children's IQ."

Who it applies to#

No one is regulated by a monograph. It is a scientific report, and NTP's page says it "may provide important information to regulatory agencies that set standards for the safe use of fluoride." Its audience in a dental office is the patient who read about it and the team member who has to answer. The group the evidence speaks to is children, including prenatal exposure, in places where total fluoride intake exceeded 1.5 mg/L equivalents: the summary page names Canada, China, India, Iran, Pakistan and Mexico as the source countries.

The American Dental Association reviewed the monograph and, in a press release dated August 26, 2024, said it "does not provide any new or conclusive evidence that should necessitate any changes in current community water fluoridation practices," that "none of the studies on IQ included in the NTP's review were conducted in the U.S. and were instead from areas with high levels of naturally-occurring fluoride," and that studies at recommended fluoridation levels "have not consistently or reliably demonstrated effects on cognitive development." ADA News the next day characterized the exposures in the monograph's conclusion as "more than double" the 0.7 mg/L that the CDC recommends, and reported the ADA's criticism of NTP's methods and peer-review process. The ADA statement and the monograph agree on the two numbers; where they differ is what to make of the gap between them.

What changed#

Draft versions of this review circulated from 2019 onward and were reviewed twice by the National Academies of Sciences, Engineering, and Medicine and then, in 2023, by a working group of NTP's Board of Scientific Counselors, which met on May 4, 2023. The literature search was extended through October 2023 for an Addendum, and the monograph says that update "did not result in a change to the earlier moderate confidence conclusion." The final version is the first NTP document on the question with a stated confidence level, and it is the report that policy arguments about fluoridation now cite on both sides, usually by quoting one of its two key sentences and not the other.

For a practice, what changed is the question at the chair. Before 2024 a patient asking about fluoride and IQ was rare; since the monograph, and the January 2025 meta-analysis, it is routine, and the answer has to be accurate about what the report found and what it declined to find.

Where the source is#

NTP's abstract page for Monograph 08 links the full 324-page PDF, which is free and in the public domain; the Executive Summary and the "About This Monograph" page carry the conclusions quoted here. NTP's completed-evaluations page for fluoride summarizes the findings in plain language, lists the protocol revisions, the National Academies reviews and the Board of Scientific Counselors materials, and describes the JAMA Pediatrics meta-analysis, which itself sits behind the journal's site. The ADA press release and the ADA News article are on ada.org.