Fluoride is a naturally occurring mineral that is good for teeth at low doses and harmful at high doses. Nobody serious disputes either half of that sentence. The real argument is about where the line sits, and whether Australia's water levels (0.6 to 1.1 mg/L) are comfortably below it for everyone.
How much fluoride Australians get
Australia's Nutrient Reference Values set an Upper Level of 10 mg a day for adults and teenagers from 9 years. For young children the limit is set by body weight (0.2 mg per kg a day since a 2017 revision). Fluoridated water is the main source for most people, followed by toothpaste that gets swallowed, tea and food. A strong cup of black tea can contain three times as much fluoride per litre as fluoridated tap water.
Established risks
Dental fluorosis
The one effect health authorities openly accept at Australian levels. About 1 in 6 Australian children has some fluorosis, almost all faint white marks, and just under 1% has more noticeable fluorosis. The main cause is young children swallowing toothpaste. Full guide.
Skeletal fluorosis
A bone disease from long-term high intake. The World Health Organization says it "may be observed when drinking-water contains 3-6 mg of fluoride per litre", and crippling skeletal fluorosis usually needs water above 10 mg/L. The Australian Drinking Water Guidelines say risk rises progressively with regular consumption above about 4 mg/L. That's four or more times Australian dosing levels, but some remote bore supplies in Queensland and the NT carry natural fluoride above the 1.5 mg/L guideline. US case reports have also documented skeletal fluorosis in people who drank extreme amounts of strong tea for years.
Disputed or unresolved
IQ and brain development
The most active debate. A 2024 US government review found "moderate confidence" that exposures above 1.5 mg/L are linked to lower child IQ, and couldn't say whether lower levels have an effect. Australian studies have found no effect. Our full breakdown of the IQ research.
Thyroid
A 2015 study of English GP practices found areas with fluoride above 0.3 mg/L were at least 30% more likely to have high rates of underactive thyroid. It was criticised for not adjusting for age and sex, and its lead author had campaigned against fluoridation. A 2017 Canadian study of more than 5,000 people found no link between fluoride and diagnosed thyroid conditions.
Bone cancer (osteosarcoma)
A 2006 exploratory US study found an association in young males exposed at ages 6 to 8. Larger follow-up studies in 2011 and 2020 found no increased risk.
Kidney disease
People with poor kidney function clear fluoride more slowly; the Australian Drinking Water Guidelines note they can retain up to three times as much. Kidney Health Australia supports fluoridation and found no link to kidney disease at optimal levels. The US National Kidney Foundation dropped its support in 2008 and says people with chronic kidney disease should be told of the potential risk.
What Australia's health authorities say
The NHMRC's 2017 statement recommends fluoridation as safe and effective, and reported no association with cancer, Down syndrome, lowered IQ or hip fracture at Australian levels. It found no reliable evidence of links to kidney disease, heart disease, high blood pressure or low birth weight. That advice is now being reviewed in 2026.
The bottom line
At Australian water levels, the only well-established side effect is mostly mild dental fluorosis. The open questions are about pregnancy, infants on formula, people with kidney disease and heavy tea drinkers, whose total intake can be much higher than average. If you want to reduce your intake, the biggest levers are filtering drinking water, supervising children's toothpaste use, and watching tea. Talk to a doctor or dentist about your own situation.