Fluoride Free NZ challenges new ‘flawed’ study

An open letter sent to members of New Zealand’s Parliamentary Health Select Committee is calling for an immediate halt to the country’s community fluoridation programmes, arguing that new research being cited in support of fluoridation contains “serious methodological flaws” and should not be used to claim the practice is safe.

The letter, published on the Fluoride Free NZ (FFNZ) Substack, circulated after legacy media reports highlighted a recently published study suggesting fluoridation does not affect IQ.

FFNZ argue the study fails to properly measure early-life fluoride exposure—widely considered the most vulnerable period for neurodevelopment. Critics note the study did not establish fluoride levels during pregnancy or early childhood, nor did it record individual fluoride exposure, instead relying solely on the location of a child’s school at the time they sat exams.

The letter also argues the research was not an IQ study at all, as it used school exam results as a proxy. FFNZ say this approach overlooks key elements of IQ assessment, particularly non-verbal performance measures such as spatial reasoning, attention, and visual-motor integration.

Citing the U.S. Government’s National Toxicology Program (NTP), FFNZ say last year’s systematic review found fluoride to be neurotoxic at exposure levels comparable to those experienced by populations drinking water at 0.7ppm—lower than New Zealand’s target level of 0.85ppm. They argue that when an appropriate margin of safety is applied, fluoride concentrations would need to be no higher than 0.15ppm to protect all at-risk groups.

The open letter also references the broader body of fluoride-IQ research, asserting that 87 out of 100 published studies have found fluoride exposure associated with reduced IQ. The authors note that only 12 studies have reported no adverse effect and that the highest-quality studies—those conducted in Canada and Mexico—did measure both fluoridation status and individual fluoride levels.

Further, the letter points to a stratified review undertaken by NTP researchers this year, which reportedly found evidence of harm below 1.5ppm, as well as a US Federal Court ruling last year that fluoridation “posed an unreasonable risk to health” under the Toxic Substances Control Act.

Dr Jonathan Broadbent, author of New Zealand’s only fluoride-IQ study, has previously said ongoing research is essential and that the outcomes of new fluoridation programmes must be closely monitored.

The letter concludes that “it can no longer be said the science is settled” and urges the Health Select Committee to recommend the immediate suspension of fluoridation across New Zealand while further investigation is carried out.

Image credit: Cottonbro Studio