Science Questions

Is fluoride in drinking water harmful?

Sat, 6th Aug 2011

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Erik Turner asked:

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 -  Itís really interesting the fact that fluoride is almost universally used in many countries.  Itís 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 Ė the normal stuff tooth enamel is made of.  So you can actually strengthen your enamel significantly and that's the reason that itís 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.  Itís 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 Ė 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 26plus 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 itís in bones, it could potentially alter the strength and the integrity of the bone architecture.  So it might make people more prone to fracture.  And there's no compelling convincing evidence that it does associate 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 Ė 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, itís being laid down as new tooth enamel in this dynamic equilibrium, and it strengthens it.  If you have too much fluoride then Ė this is one of the other things that the York study looked at Ė 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 itís 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 itís 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.


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My first inclination is to say that fluoride would have a negligible effect on the thyroid because fluoride and iodine are fairly different (despite both being halogens). I would also assume that it would pass right through the body due to the high solubility of many ionic halogen compounds.

I researched it on a couple of University library websites, and found that there are numerous articles addressing this topic. A couple that might help are: "Fluorine and thyroid gland function: a review of the literature," "Effects of fluoride in drinking water on health of deciduous teeth" (you can google these titles and get at them free), there is also a book entitled "Fluoride in drinking-water" that might help (I have not read it). If someone with some more expertise could comment that would be great, I feel like I'm grasping at straws here. Bill.D.Katt., Thu, 2nd Jun 2011

If fluoride interfered with iodide in the thyroid then chloride would do so to a much greater extent. It doesn't so fluoride can't.
They add fluoride to water because it slows tooth decay.
High levels of fluoride in water are toxic, but nobody adds that much.
The first symptom of chronic fluoride exposure is mottled teeth. If you don't see that effect in the local kids then you are safe (even if you do see it then you are probably OK).
Very high levels of fluoride are acutely toxic, but that's very rarely seen. Bored chemist, Thu, 2nd Jun 2011

Fluoride only accumulates in bones, which I believe is the point. Madidus_Scientia, Thu, 2nd Jun 2011

Fluoride makes dense, but WEAK bone.  So, it is not a good treatment for osteoporosis. 

I believe studies indicate that children with fluoridated water have better teeth.  I believe some cities have been using fluoride for 50 years or so, so one should be able to get real data about the teeth in people who are in their middle ages, and perhaps even bone strength.

Here is a study about bones.

It seems to indicate the lowest rate of bone fractures with a concentration of Fluoride at about 1ppm.  More fractures with lower concentrations of fluoride, as well as with higher concentrations of fluoride.  However, the study also has some very large error bars.

I'm having troubles finding data on tooth decay.
Here is a chart that seems to show no significant difference in tooth decay in 12 yr olds living in countries with fluoridated water compared to those that live in countries without fluoridated water.

In fact, if a community showed improvements from 1970 to 2000 with an uncontrolled study, then those improvements were likely independent of the fluoridation program.

I'm seeing other articles with people expressing major concerns about the safety of the fluoridation. 

What I'd really like is not to see tooth data in 12 yr olds, but rather seeing tooth data on 40 to 70 yr olds. CliffordK, Thu, 9th Jun 2011

The real data was around before they started adding fluoride to drink it came from areas where there is natural fluoride in the water.
That data is the reason they started adding it to water. Bored chemist, Thu, 9th Jun 2011

Hello Naked Scientists, my friend posted a comment on facebook about thyroid function, particularly in women, being negatively affected by fluoride. She cited the following book. Please comment: Lydia Jane Cypher, Sun, 14th Aug 2011

The toxicity of fluoride is well documented and if you were to read the research coming out of Europe where flouring is banned in a high number of countries you would see the horrible truth. First the fluoride is water is not the same fluoride we find in nature. The product added to our water is a waste product from pesticide and fertilizer manufacturing. Second fluoride is a highly persistent chemical which is difficult to very difficult to remove from the body. Just as you claim that it bonds to teeth and bones it also bonds very well to our cells forming cocoons around each cell. This cocoon blocks the nutrients from reaching the cell and it dies. The fluoride then moves to the next cell. Simply put, the body is starved to death over a long period of time. Ask yourself while infant toothpaste does not contain fluoride. Ask your self how a small animal will die from ingestion of a tube of tooth paste. Take it out of our water as it's so over used. Its in our water, tap and bottles, its in all soda and bear. Its in out fruits and vegetables and the animal products we eat. When do we realize this is so very wrong! Creed, Wed, 13th Mar 2013

Is this even a serious question?  In 1945, "Program F" was implemented by the U.S. Atomic Energy Commission (AEC). This is the most extensive U.S. study of the health effects of fluoride, which was the key chemical component in ATOMIC BOMB PRODUCTION. One of the most toxic chemicals known to man, fluoride, it is found, causes marked adverse effects to the central nervous system but much of the information is squelched in the name of national security because of fear that lawsuits would undermine full-scale production of atomic bombs. 

They knew this in the 1940's and the big push began to put fluoride in drinking water nationwide in the '50's.  I wonder why.
frenchconnection, Mon, 30th Jun 2014

Because it was found that people living in areas with detectable natural fluoride levels in drinking water, had significantly less tooth decay than others, and no contraindications. The effect on dental health in the UK has been remarkable, and despite all the scaremongering, we live longer than ever before - with less tooth decay!

But who cares about the facts? Science is boring. Let's tell each other scary fairy stories about government conspiracies to poison everyone. alancalverd, Mon, 30th Jun 2014

Many years ago, my dentist said that I was about the youngest of his patients who suffered traditional dental decay. This is because my adult teeth came through just before the water in my home city was fluoridated.

Younger children had the fluoride built into their adult teeth, and this made them much tougher.

He commented that the main dental threat to this younger generation was from acidic soft drinks, which attacked the teeth directly. evan_au, Mon, 30th Jun 2014

1 yes it's a reasonable question because it's sometimes difficult to tell the real (but dull) story from all the conspiracy nonsense.
Got any references to real scientific papers? The only stories I saw about "program F"  as junk on conspiracy site.
3 Well, since they do use fluoride in the manufacture of bombs, it's good to know that they were checking the effects it had on the workforce. People seem to forget that the point of the military is to kill the enemy's guys- not your own.
However, the key use of fluoride in uranium processing is in a chemical called uranium hexafluoride.
There's no question that the stuff is bad for you. But the real problem there is the uranium- which, in addition to being radioactive, is also rather poisonous.

The claim that fluoride is one of the most toxic chemicals known is true- but only in the same way that I'm one of the most attractive men on the planet. There are about 4 billion men and I'm among the most attractive 3,999,999,999.
True but meaningless.
There are plenty of chemicals much more toxic than fluorides. (as an aside, the really toxic ones like ricin and BTX are natural, rather than man made.)
5 They did, indeed, know about fluoride in the 40s and by the 50s they had realised that adding it to the water (where nature didn't do this for us) would improve our teeth. Among the things they knew was that the first symptom of low level toxicity is mottling of the teeth. As long as you keep the concentration low enough to avoid that (and they do) there are no detectable toxic effects.

6 to reduce the degree to which our teeth suffer from decay. Bored chemist, Mon, 30th Jun 2014

It never hurts to have large blinded studies, or perhaps re-analyze the data, especially as more and more municipalities are adding fluoride to their water.  But, enough don't add fluoride, that there is always comparative data.  Fluoride toothpaste?

As BC mentioned, there are lots of toxic chemicals.  High doses of Chlorine is also toxic.  Yet, it is part of one of the most common food flavorings in the world, and chlorine is important to providing safe drinking water. CliffordK, Mon, 30th Jun 2014

Thousands of people are killed by water every year. Bloody dangerous stuff - ought to be banned. But there is a multinational conspiracy to take the natural product, remove all the natural organisms that live in it, make it completely tasteless and odorless, and pipe it straight into people's homes. The conspiracy is so pervasive that even wellmeaning charities have been bamboozled into supporting it and delivering this dangerous substance into primitive villages where people have lived a natural existence for thousands of years.

Just because it is a natural constituent of beer doesn't make it safe. All sorts of lethal chemicals like chlorine and ozone are added to it to destroy the balance of its ecosystem. alancalverd, Tue, 1st Jul 2014

OK, I apologise: I should know better but...

Is this even a serious question?  In 1945, "Program F" "Program W" was implemented by the U.S. Atomic Energy Commission (AEC). This is the most extensive U.S. study of the health effects of fluoride water, which was the key chemical component in ATOMIC BOMB PRODUCTION. One of the most toxic chemicals known to man, fluoride water, it is found, causes marked adverse effects to the central nervous system but much of the information is squelched in the name of national security because of fear that lawsuits would undermine full-scale production of atomic bombs.  They knew this in the 1940's and the big push began to put fluoride water in drinking water nationwide in the '50's.  I wonder why.
OK, so I'm parodying it, but is anything in the new version any more wrong than in the first? Bored chemist, Tue, 1st Jul 2014

Nope, this seems like nothing more than "Chemophobia" and nothing more. SorryDnoodle, Thu, 3rd Jul 2014

As was noted centuries ago "dose makes the poison."

It is true that fluoride is very toxic and even corrosive at high concentrations (high doses), but every substance has a level at which it is toxic (this includes such innocuous chemicals as water, oxygen, nitrogen, sugar...) More important than identifying a substance as toxic, is identifying the dose at which toxic effects are manifested. In the case of compounds used to improve quality of life, the question really should be "at what level is the maximum net positive effect?"

It would appear that the fluoride levels used are very far below the toxic threshold, and have a measurable positive influence on tooth health.

Also, I want to take issue with the argument that "the fluoride in water is not the same fluoride we find in nature.  The product added to our water is a waste product from pesticide and fertilizer manufacturing."---Fluoride is fluoride. Unless they are somehow using some other isotope of fluorine (which they aren't), or are somehow contaminating the fluoride with traces of the pesticide, the fluoride produced by these processes is identical, in every way, to "natural" fluoride (which is most likely the source of the precursors for pesticide manufacture anyway)

If I were you, I would worry more about the chemicals that made it into the drinking water by accident than those that are put there on purpose. chiralSPO, Mon, 7th Jul 2014

The bit about
"the fluoride in water is not the same fluoride we find in nature.  The product added to our water is a waste product from pesticide and fertilizer manufacturing."
is wrong, but has some basis in reality.
What is added to water is not (usually) fluoride but fluorosilicate.
That is indeed a by-product from the manufacture of phosphate fertiliser.
(calling it "waste" makes as much sense as describing my leather shoes as "waste" from the meat industry, but the anti-fluoride lobby like to put a bad spin on things if they can).
Part of the reason they use it is that it's cheap.
But the real advantage to using fluorophosphate (rather than fluoride) is that it's
ermm, well, how to put this.

It's less toxic.

Odd thing to choose to complain about.

Now, if you want to look at other  fluorine compounds you might be interested in fluoroacetates.
They are rather more toxic than fluorides, They are actually used as pesticides(well they were, they got phased out because they were too dangerous.)
I think it's interesting to look at the sort of plant people used to manufacture this pesticide
Bored chemist, Mon, 7th Jul 2014

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