Fluoride in the drinking water significantly cuts the rate of tooth decay in the adult population, according to the findings of a new international study on dental health conducted by the University of Adelaide.

In a world first, researchers conducted a population-level study, concluding that fluoridated drinking water is preventing tooth decay for all adults regardless of age – and significantly for those people who have had no exposure to the chemical before.

The study looked at data from a random sample of 3800 Australians aged 15 and over.

"By looking right across the Australian population, we now have good evidence that fluoride in drinking water is effective in preventing tooth decay in adults," says co-author Professor Kaye Roberts-Thomson.

"We've known for some time that fluoridated drinking water can prevent tooth decay in children, but this is the first time that research has conclusively shown this in an adult population."

The results show that adults with more than a 75% lifetime exposure to water fluoridation have significantly reduced tooth decay (up to 30% less) when compared with those with less than 25% lifetime exposure.

"Those people who have had longer exposure to fluoride in water obviously will have the greater benefit. However, and this is an important aspect of the study, even those people who were born before water fluoridation existed have since received some benefit in their lifetimes," Professor Roberts-Thomson says.

"Given the ongoing controversy surrounding fluoridated water, especially in some parts of Australia, we should point out that the evidence is stacked in favour of long-term exposure to fluoride in drinking water. It really does have a significant dental health impact."