Science Advocacy
Science Advocacy
Welcome to “chemicals and society”, where we highlight the current understanding of the biological effects and safety of some of the most common chemicals in today’s society.
What is fluoride?
Fluoride is the anion of fluorine, the element with an atomic number of 9. An anion is a negatively charged particle (represented as F‾), and fluoride occurs naturally when it is released from fluorine-containing minerals like calcium fluoride. Fluorine is pretty common on earth – it’s the 13th most common element, and people are exposed to it mainly in their food and water. However, we are most familiar with fluoride from it’s use in toothpastes, mouthwashes, dental treatments, and as a drinking water additive.
What is fluoride used for?
Fluoride is used to prevent or delay the development of dental caries (commonly known as cavities). Cavities occur when bacteria build up on your teeth and acidify (lower the pH of) the enamel around them. This acid slowly eats away at your teeth. Luckily, your teeth can counter-act this demineralization to some degree, and that’s where fluoride comes in. It aids in the remineralization and in the process also makes teeth more resistant to future demineralization.
So how and why did people start putting fluoride in drinking water?
Fluoride occurs naturally in all water – seawater, lake water, river water, groundwater, literally all water. The actual levels of fluoride depends on the geology of the area, and it can vary widely. These different levels of fluoride in different areas of the world helped people figure out that fluoride could protect against cavities. They noticed that people living in areas with higher levels of fluoride had fewer cavities, and this eventually led to the idea that adding fluoride into water that didn’t have much in it might reduce cavities in those that drank it. The first city to fluoridate it’s drinking water was Grand Rapids, MI in 1945. Since then, much of the United States and many countries around the world have introduced fluoridation, including Argentina, Australia, Brazil, and Canada.
It may surprise you to learn that only about a two thirds of the water in the United States has fluoride added to it. This is because water in many parts of the country (and the world) has plenty of fluoride – particularly in states like Virginia and South Carolina, and western states like Colorado and New Mexico. In fact, in some of these areas, the local ground water needs to be treated to remove excess fluoride. This is because high fluoride levels can stain teeth (called dental fluorosis), and really high levels can be toxic (But more on that later).
There is absolutely no question at all that fluoride decreases the risk of cavities. Some people may state otherwise, and they are wrong. If you were to cut out all fluoride from your life (including toothpaste and dental treatment) the result would not be pretty – you would get more cavities. There is no scientific debate about this.
Water fluoridation also reduces the risk of cavities, but here there is a bit more debate about exactly how much. There are several reasons for this. Fluoridation wasn’t very well studied before it was implemented, and that is a factor. The biggest factor, however, is that there are some pretty big confounding factors that make it difficult to study the effect of water fluoridation on cavity rates. A confounding factor is something that affects an outcome (in this case rates of cavities) in a way that is independent from the factor you are trying to study (in this case fluoride). The biggest confounding factors here are socioeconomic status (SES) and use of fluoride toothpaste and dental treatments. People with a lower SES (poorer individuals and their kids in particular) are at a higher risk to develop cavities than higher SES individuals and their kids, regardless of fluoridation status. There are probably a host of reasons for this – people with lower SES tend to eat more poorly, with higher levels of sugar in their diets, and they are also less likely to use fluoride-containing toothpaste and see a dentist regularly. This is the second confounding factor – the use of fluoride-containing toothpaste and dental treatments. You can’t compare cavity rates in populations with different access to these sources of fluoride, and SES is a factor in their availability.
This makes comparing different populations to look at an effect of fluoridation difficult. For instance, the city of Portland OR has not fluoridated their water for years (I know, don’t get us started). Some will point out that Portland’s rates of cavities are better than some other cities that do fluoridate their water, but you can’t do this without controlling for SES and access to fluoridated dental care. Portland is a wealthy, thriving city with highly educated, higher SES residents – you can’t compare them to less prosperous cities, it’s apples to bananas. Portland doesn’t have the highest rates of tooth decay in the country, but it’s rates are not good.
Since the advent of fluoridated toothpaste and dental treatments, the rate of cavities has been dropping all across the world, in areas with and without fluoridated water. That makes it difficult to compare rates in the same city across time. Do do this, you need a recent example of a city that suddenly stopped fluoridating it’s water, and then you would need to do a well-controlled study to account for differences in SES and access to dental care. Luckily, there is one such example – Calgary, Alberta.
Calgary is a perfect example – a city with a relatively good standard of living and similar access to dental care across different SES categories due to Canada’s universal healthcare (must be nice). Their city council also decided to stop fluoridating their water supply in 2011. A group of researchers studied the effects of this change on the children of Calgary and saw a significant increase in the rates of cavities even when accounting for SES. This is in line with large scale studies in other countries that have shown a clear decrease in the rates of cavities in children living in areas with fluoridated water compared to those living in unfluoridated areas. It is less clear that fluoridation helps prevent cavities in adults.
Taken together, the data in support of fluoridation of water supplies are extremely strong:
Is fluoridation safe?
Some people will tell you that fluoride is toxic. Other will tell you it is perfectly safe. They are both right. In order to understand how this is possible, we have to understand the dose-response of fluoride’s biological effects. A dose-response relationship is a fundamental part of biology, and particularly the fields of pharmacology and toxicology – it’s a way to express what doses of a chemical cause biological effects – good or bad.
The only known beneficial effect of fluoride is on dental caries. Fluoride is not an essential mineral, though everyone has some fluoride in their bodies at all times. The optimum level for the prevention of cavities is about 1 mg/L (the US EPA recommended level is 0.7 mg/L).
The EPA lowered the level to 0.7 mg/L (from a recommended range of 0.7-1.2 mg/L) because dental fluorosis starts to occur at in this range. The staining caused by these levels of fluoride is pretty minimal, so it’s not a concern for most people, but at higher levels, it can be more noticeable. Keep in mind that fluorosis is just cosmetic staining of the teeth.
The World Health Organization (WHO) has set the maximum safe level of fluoride at 1.5 mg/L, and most areas in the developed world with natural levels higher than this use filter systems to reduce the levels of fluoride. Levels above this can led to skeletal fluorosis, which causes the bones to become brittle and break easily. At very high levels, fluoride can damage the stomach and parathyroid glands as well.
There are some reports suggesting that fluoride may have a small negative effect on IQ in children exposed to high levels, but the link between brain development, IQ and fluoride is not well established, and the risk is likely only at levels well above those added to water in the United States. There have been a few cases where mistakes were made during water fluoridation and large amounts were release into the water supply all at once- this acute fluoride poisoning causes nausea, vomiting, and diarrhea, but these incidents are rare, and fairly obvious when they occur.
What’s the bottom line?
Water fluoridation has become controversial in the United States for a number of reasons. While claims that fluoride is dangerous or “toxic” are simply untrue, anti-fluoridation advocates often point out that it is added to our water without our direct consent and that it is the only chemical added to water for the purpose of medical treatment. These statements are correct, however, there are many other chemicals added to drinking water to disinfect or clarify it, and chemicals like iodine and vitamin D are added to our food (salt and milk, respectively) without our consent every day. People consume these chemicals at low levels without direct consent as well. While false claims about fluoride toxicity are often part of the anti-fluoridation argument, the main driver behind it seems to center on freedom of choice and vague conspiracy theories about the government trying to poison us all. Lost in these arguments is the fact that no matter where you get your water, there is fluoride in it already.
While some people might bristle at being essentially forced to drink water that helps reduce the risk of cavities, the United States government has to look at things in a different way. Cavities cost money – they have to be diagnosed and filled, and over time a mouth full of cavities may require implants and dentures. People will miss time at work for these procedures too. Dental insurance will cover most of these procedures, and it adds up. Studies estimate that fluoridation saves between $24-$61 per year per person depending on which state you live in (and the natural fluoride levels in that state). There are over 300 million people in the United States, so this kind of savings is enormous (over 7 billion dollars a year), and it is this cost savings that is the main driver behind continued fluoridation in the United States.
In this way, water fluoridation is very similar to another government-mandated safety practice which has been codified as law – seat belt laws. While you may hear similar complaints about the government impinging on personal freedom by requiring the use of seat belts, the driver (ha! risk assessment pun!) here is the same – if everyone wore seat belts, it is estimated that the United States would save about 26 billion dollars a year. Preventing cavities isn’t nearly as exciting as saving lives, but the economic impact is almost as big. This is why the CDC named water fluoridation as one of 10 greatest public health achievements of the 20th century.
