Australia's National Health and Medical Research Council (NHMRC) has released a report concluding that water fluoridation, as used in several countries, is safe and beneficial against tooth decay. The findings largely replicate a previous NHMRC study, but represent the most comprehensive survey of work on the topic ever released.
The report concludes: “Water fluoridation reduces tooth decay by 26-44% in children, teenagers, and adults.” On the other hand, the only negative health effect associated with fluoridation is fluorosis, a discoloring of the teeth that some consider unattractive, but is usually too faint to be seen outside a dental exam. Specifically, no association was found with cancers or reduced cognitive functions.
The report was conducted in response to concerns in the community about fluoridation, including rumors widespread enough to have caused some rural Australian councils with very high rates of tooth decay to reject the process.
Spend much time on social media, particularly if you live in a country that fluoridates its water supply, and you'll probably encounter these allegations. Fluoride, posts claim, is a neurotoxin and adding it to the water supply is slowly killing us all. The gentler ones argue fluoridation is all a terrible mistake, but others see the hand of a global conspiracy to suppress the population or destroy our intelligence.
The latter groups are ridiculous, but the "mistake" claim was sufficiently plausible to prompt the NHMRC to investigate. After all, fluoride is toxic in sufficient doses. So is almost everything else, but it is true that you need a lot less fluoride before it gets unhealthy than most other substances we consume. In many parts of the world, fluoride levels in the water supply are naturally high enough that the World Health Organisation recommends taking some out.