Is fluoride in drinking water harmful?

07 August 2011



Hello Naked Scientists,

My wife has recently become concerned about fluoride in drinking water here in the United States. She is concerned about the long term effects of fluoride that accumulates in our bodies since fluoride is a poison. She also thinks that fluoride may have contributed to her thyroid problems since it replaces iodine.

Is there any solid science to show that fluoride in drinking water is dangerous to our health? There is a lot of information on both sides of the debate on the Internet, but I don't know who else to trust other then the Naked Scientists.

Love the show and keep up the good work,

Atlanta, Georgia


Chris - It's really interesting the fact that fluoride is almost universally used in many countries. It's done because there's an understanding of the chemical reason that fluoride strengthens tooth enamel.

Tooth enamel contains the chemical apatite which is a form of calcium phosphate. If you add fluoride to the diet, either in food, in salt, in drinking water, then you can add a fluoride atom to the forming calcium phosphate and you get flouro-apatite and this is much harder than just normal hydroxy-apatite - the normal stuff tooth enamel is made of. So you can actually strengthen your enamel significantly and that's the reason that it's done because it can give people very strong, very good quality teeth.

If you look at the levels of tooth decay that have happened since this actually was introduced, levels of tooth decay have plummeted in many places that fluoridate their water. In fact, studies have been done looking at this effect and it seems to suggest that the number needed to treat, in other words, the number of people who you have to get to drink fluoridated water in order to stop having cavities who otherwise would is about 6.

So, for every 6 people who drink fluoride-laden water, one person will not to get cavities who would otherwise have done. So that's amazing actually. It's a very big health impact.

But then there's a question: Are there any health disbenefits? And this is where it gets a bit murky because actually, there's very little good quality published evidence - one way or the other.

There was a very big meta analysis that was performed by the University of York, which is probably the gold standard and has been cited by agencies and organisations all over the world since. What they actually say is they have taken 26-plus studies that have looked at fluoride in water and looked at the health benefits - no cavities - and some of the disbenefits. So for instance, do people who have been drinking fluoridated water have more hip fractures for example? Because if it gets into teeth, it can also get into bones, and if it's in bones, it could potentially alter the strength and the integrity of the bone architecture. So it might make people more prone to fracture. There's no compelling convincing evidence that it does associate with more fractures.

They've done a similar thing for cancers and not found any association with cancers, but the University of York team say, actually, the level of evidence is quite poor and really, we do need some very big trials and some big studies in order to look at this properly because the evidence is really quite scant.

Dominic - Obviously, a lot of people use fluoride toothpaste or fluoride mouthwash, but what additional benefit does fluoride in the water give?

Chris - The tooth enamel is in a dynamic equilibrium. So, if you have acid in your mouth then you can erode some of the enamel. If you shift it towards an alkaline environment and there's calcium present, and some fluoride, you can rebuild some enamel. So what the toothpaste is aiming to do is to supply you with a ready source of alkaline environment - that's why there's bicarbonate in it - and some calcium, and some phosphate, and they put fluoride in there because then it gets into the matrix, it's being laid down as new tooth enamel in this dynamic equilibrium, and it strengthens it.

If you have too much fluoride then - this is one of the other things that the York study looked at - you can get something called flourosis. People who live in Essex especially (I was one of them), if you drink lots and lots of tap water and are exposed to fluoride, there's very high levels of fluoride in the water that you drink, and this can get impregnated into the teeth and it's more likely to cause tooth staining and you get a speckledy pattern on the teeth.

You'll never get cavities. They won't look that aesthetic but you never get any tooth decay and I've never had any fillings in my entire life. My teeth are really good actually and I put it down to the fact that partly I was from Essex, so there are some benefits of being in Essex apart from the fact that it's got some of the best schools in the country, it does have very good water as well, and I think cleaning your teeth very regularly with a toothpaste laden with fluoride is very, very important.


They wear gas masks and hazard suits while dumping fluoride into the water supply. The barrels of fluoride have hazard warnings on them. Guess what I would assume from that.

When handling a concentrated source material the risks are quite different from when that substance is diluted millions of times. Chlorine at low concentration in a swimming pool keeps the water safe and clean; the source gas at high concentration, on the other hand, will kill you quite effectively.

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