Fluoride in tap water lowers children’s IQ

What the research found

A 2025 systematic review and meta-analysis of 74 studies found most reported lower IQ with higher fluoride exposure. Most were cross-sectional, and 52 were rated high risk of bias. A 2023 dose-response review found about 3 IQ points lower per 1 mg/L of water fluoride between 1 and 2 mg/L. A 2018 meta-analysis also linked high water fluoride to lower intelligence.

The US National Toxicology Program had moderate confidence that fluoride above 1.5 mg/L in drinking water is linked to lower child IQ. It said there was not enough data to tell whether 0.7 mg/L, the US recommended level, affects IQ. It also stressed that an association does not prove cause and effect.

Reviewers disagree on cause. A 2024 toxicology review rated the evidence for lower IQ as strong, but noted uncertainty about causation. A 2024 commentary said evidence of causation is lacking. A 2026 analysis found no significant effect in five studies done in fluoridated areas, and said maternal urine studies were not good enough to combine. Australia's NHMRC found no reliable evidence that fluoridation at current Australian levels causes health problems.

What it doesn’t mean

• This does not show that Australian tap water lowers IQ. Most of the concerning studies looked at higher fluoride levels, and most were done in countries such as China and India.
• The studies add up fluoride from all sources, not just tap water. Many were cross-sectional and could not rule out other explanations. NHMRC's evidence evaluation found that water fluoridation helps reduce tooth decay in children and adults.
• If you are unsure how much fluoride your child gets, ask your GP, dentist or child health nurse.