The Research on Fluoride and IQ

Robert F. Kennedy Jr. has recently mentioned research linking fluoride to lower IQs (see here). The August 2024 release that he mentions led to a publication in JAMA Pediatrics in Jan. 2025 that was a “systematic review and meta-analysis of 74 cross-sectional and prospective cohort studies,” and that “found significant inverse associations between fluoride exposure and children’s IQ scores.”

It’s not clear what he intends to do in the future as to any alleged link between fluoride and IQ (or what he even has the authority to do). Nonetheless, is the 2025 paper good science? Alas, no.

But wasn’t this a systematic review and meta-analysis? And isn’t that the highest tier of evidence?

In limited cases, that can be true. For example, if there are many high-quality randomized trials of the same question, analyzing that body of evidence together can give a more precise answer than one study by itself.

But in many cases, meta-analyses can be the worst of all worlds. If you take a bunch of low-quality studies and lump them together into a meta-analysis that purports to give a rigorous answer, it’s the research equivalent of money laundering. You are taking bad evidence and converting it into (the appearance of) rigorous evidence.

A number of scholars use the phrase “garbage in, garbage out” when discussing meta-analyses (see here and here, for example).

But it’s actually worse than that. It’s taking garbage and then convincing everyone it has turned into gold.

ChatGPT’s version of a factory machine turning garbage into gold

So, what about the 2025 JAMA Pediatrics article that RFK was referring to? More a case of “garbage-gold” than anything else.

Matthew B. Jané, James Heathers, and David Robert Grimes recently published a re-analysis of the piece. And does it come out looking terrible.

Among the piece’s many problems:

1. Out of 74 studies, 21 came from a publication literally called Fluoride, which is “completely unaffiliated with any professional body, scientific publisher, or academic institution.” Basically, it’s a “journal” that is nothing more than an online group of anti-fluoride activists. Hint: Doing a meta-analysis where 28% of the included studies were from a bogus activist source isn’t going to lead to true outcomes. [Many legitimate journals do publish irreproducible or inaccurate material, of course! But it’s not their sole mission; moreover, anyone doing a meta-analysis should try to adjust for the quality of the underlying research.]

2. Many of the underlying studies were simply confused as to correlation vs. causation. Indeed, “many of the included studies are no more detailed than the following: Area A has low fluoride water levels, Area B has high fluoride water levels, and Area A has higher mean IQ.” In other words, the studies compared IQ and fluoride in different regions, even if the regions had different levels of nutrition, environmental exposure, or a hundred other unmeasured factors. Such studies are “absolutely inappropriate for determining any causal relationship,” and combining those studies is trying to turn garbage into gold.

3. 18 of the 74 studies measured fluoride by urine analysis, which is “wholly unreliable.”

4. Several of the underlying studies had impossible data or extremely unrealistic effects (such as a p-value of 0.0000000000000000000000000000000000027).

This meta-analysis in JAMA Pediatrics is completely unreliable. As the reviewers say:

Were this merely yet another piece of research waste, it would be merely unfortunate, but its high altmetric scores are indicative of its likely impact on public trust and understanding. Were the errors in the work salvageable with a correction, we would recommend this. But as this analysis shows, it is flawed on multiple levels from inception to execution, and cannot simply be fixed. This combination of factors motivated this special communication, and in light of these criticisms, we can only recommend blanket retraction to mitigate its potential harms on public health not only in the USA, but worldwide.

No one at HHS should use this study as a basis for doing anything about some supposed link between fluoride and IQ. There are many better fish to fry.