https://jamanetwork.com/journals/jamapediatrics/fullarticle/2828425

It says fluoride levels of 2-4mg/L are correlated in a reduction of IQ. But technically the WHO has long since recommended a maximum of 1.5mg/L due to a risk of fluorosis which is a comparatively minor concern, though it’s hard to find information about what levels are considered safe beyond “recommendations”. Either way many places have higher than 2mg/L of fluoride in the tap water (due to natural content).

(I am not an expert on the topic and generally want to leave public health policy to those with relevant knowledge/expertise, not laypeople like us)

Possibly this? https://doi.org/10.2903/j.efsa.2025.9478 (which is possibly not a regular journal article and being unfamiliar with the European Food Safety Authority I don’t know how their publishing process works, but it’s still an evidence-based publication by the government-run EFSA)

Here’s the full abstract - the full paper is quite a long read:

Abstract

This updated risk assessment evaluated evidence on potential adverse health effects of fluoride related to all sources of oral exposure as mandated by the European Commission. Fluoride benefit assessment was not included. Effects on the central nervous system, thyroid and bone were prioritised. Evidence from human studies indicates that total fluoride intake is associated with adverse effects on the developing brain at drinking water concentrations > 1.5 mg/L. The evidence of such associations below 1.5 mg/L was not sufficiently consistent to draw conclusions for risk assessment. Using drinking water concentration of 1.5 mg/L as a reference point, a safe level of intake including all sources of oral exposure of 3.3 mg/day was established for pregnant women to protect the fetus. This safe level of intake was extended to apply to other adults and children > 8 years. It is considered protective also against possible adverse effects on thyroid function and bone mineralisation, for which associations have been observed at water concentrations > 1.5 mg/L. Dental fluorosis was considered the most sensitive endpoint for children ≤ 8 years. Tolerable upper intake levels (UL) of 1.0, 1.6 and 2.0 mg/day were established for infants, toddlers and children 4–8 years, respectively. These ULs are considered protective against other possible adverse effects of fluoride, including neurodevelopmental outcomes. Aggregate exposure included intake of fluoride from food, drinking water, discretionary salt and (ingested) dental care products. Aggregate exposure based on the mean concentration of fluoride in EU drinking water (submitted data) was below the above health-based guidance values (HBGVs) for all age groups. Aggregate exposure exceeds the HBGVs at the 95th percentile of intake in the scenario of the P95 concentration of fluoride in EU drinking water, for all age groups except adolescents. The risk assessment suggests that the current legal limit for drinking water (1.5 mg/L) in the EU is not sufficiently protective. (emphasis added)

This is from July of this year so it might match up with what Tenderizer is remembering.

The EFSA has a plain language summary that’s targeted for the general population rather than the slog of the above paper which isn’t. Quoting what I believe is most relevant from the “Outcomes” section:

• It was found that if fluoride concentrations in drinking water were at the EU legal limit of 1.5mg/L, this would lead to a total fluoride exposure above the newly determined ULs and safe level of intake.

• Actual drinking water concentration data submitted to EFSA indicated that more than 86 % of samples contained less than 0.3 mg/L fluoride, and more than 97 % of samples contained less than 0.7 mg/L fluoride.

• Based on these data, EFSA estimated that for typical fluoride concentrations in drinking water in Europe total fluoride exposure does not exceed the safe level of intake or the ULs determined for the different age groups (except in 4-8-year-old children) and therefore does not pose a health concern.

For context, Australian water:

Typical values in Australian drinking water

In unfluoridated supplies, fluoride concentrations are typically less than 0.1 mg/L, but can range from less than 0.05 mg/L up to 1.5 mg/L, with the higher values reported from groundwater sources.

In fluoridated supplies, the target fluoride concentration is between 0.7 and 1 mg/L, with the lower concentrations applying where the climate is hot, to allow for a higher average consumption of water.