Fluoride is a chemical commonly added to toothpaste.

It has a unique ability to prevent tooth decay.

For this reason, fluoride has been widely added to water supplies to improve dental health.

However, many people are concerned about the potential harm from excess intake.

This article takes an in-depth look at fluoride and examines how it can affect your health.

What Is Fluoride?

Fluoride is the negative ion of the element fluorine. It is represented by the chemical formula F-.

It is widely found in nature, in trace amounts. It occurs naturally in air, soil, plants, rocks, fresh water, sea water and many foods.

Fluoride plays a role in the mineralization of your bones and teeth, a process essential for keeping them hard and strong.

In fact, about 99% of the body’s fluoride is stored in bones and teeth.

Fluoride is also important for preventing dental caries, also known as cavities. This is why it has been added to community water supplies in many countries (1).

Bottom Line:

Fluoride is the ionized form of the element fluorine. It is widely distributed in nature and supports the mineralization of bones and teeth. Fluoride may also help prevent cavities.

Sources of Fluoride

Fluoride can be ingested or applied topically to your teeth.

Here are some of the major sources of fluoride:

  • Fluoridated water: Countries like the US, the UK and Australia add fluoride to their public water supplies. In the US, fluoridated water generally contains 0.7 parts per million (ppm).
  • Groundwater: Groundwater naturally contains fluoride, but the concentration varies. Typically, it’s between 0.01 to 0.3 ppm, but in some areas dangerously high levels are present. This may cause serious health problems (2).
  • Fluoride supplements: These are available as drops or tablets. Fluoride supplements are recommended for children over 6 months of age who have a high risk of developing cavities and live in non-fluoridated areas (3).
  • Some foods: Certain foods may be processed using fluoridated water or may absorb fluoride from the soil. Tea leaves, especially old ones, may contain fluoride in higher amounts than other foods (4, 5, 6).
  • Dental care products: Fluoride is added to a number of dental care products on the market, such as toothpaste and mouth rinses.
Bottom Line:

Fluoridated water is a major source of fluoride in many countries. Other sources include groundwater, fluoride supplements, some foods and dental care products.

Fluoride Helps Prevent Dental Cavities

Dental caries, also known as cavities or tooth decay, are an oral disease (7).

They’re caused by bacteria living in your mouth.

These bacteria break down carbs and produce organic acids that can damage tooth enamel, the mineral-rich outer layer of a tooth.

This acid can lead to loss of minerals from the enamel, a process called demineralization.

When the replacement of minerals, called remineralization, does not keep up with minerals lost, cavities develop.

Fluoride may help prevent dental cavities by (8):

  • Decreasing demineralization: Fluoride may help slow down the loss of minerals from the tooth enamel.
  • Enhancing remineralization: Fluoride may accelerate the repair process and help put minerals back into the enamel (9).
  • Inhibiting bacterial activity: Fluoride is able to reduce acid production by interfering with the activity of bacterial enzymes. It may also inhibit the growth of bacteria (10).

In the 1980s, it was demonstrated that fluoride is most effective in preventing cavities when applied directly to the teeth (11, 12, 13).

Bottom Line:

Fluoride may fight cavities by improving the balance between mineral gain and loss from the tooth enamel. It may also inhibit the activity of harmful oral bacteria.

Excessive Intake Can Cause Fluorosis

Excess intake of fluoride for long periods of time can cause fluorosis.

Two main types exist: dental fluorosis and skeletal fluorosis.

Dental Fluorosis

Dental fluorosis is characterized by visual changes in the appearance of teeth.

In mild forms, the changes appear as white spots on teeth and are mostly a cosmetic problem. More severe cases are less common, but are associated with brown stains and weakened teeth (14).

Dental fluorosis only occurs during the formation of teeth in childhood, but the most critical time is under the age of two (15).

Children consuming too much fluoride from multiple sources over a period of time have a higher risk of dental fluorosis (16).

For example, they may swallow fluoridated toothpaste in large amounts and consume too much fluoride in supplement form, in addition to ingesting fluoridated water.

Infants who get their nutrition mostly from formulas mixed with fluoridated water may also have an increased risk of developing mild dental fluorosis (17).

Bottom Line:

Dental fluorosis is a condition that alters the appearance of teeth, which in mild cases is a cosmetic defect. It only occurs in children during the development of teeth.

Skeletal Fluorosis

Skeletal fluorosis is a bone disease that involves the accumulation of fluoride in the bone over many years (18).

Early on, symptoms include stiffness and joint pain. Advanced cases may eventually cause altered bone structure and calcification of ligaments.

Skeletal fluorosis is particularly common in countries like India and China.

There, it’s primarily associated with the prolonged consumption of groundwater with high levels of naturally occurring fluoride, or more than 8 ppm (2, 19).

Additional ways people in these areas ingest fluoride include burning coal in the home and consuming a particular type of tea called brick tea (20, 21).

Note that skeletal fluorosis is not an issue in regions that add fluoride to water for cavity prevention, since this amount is tightly controlled.

Skeletal fluorosis only happens when people are exposed to very large amounts of fluoride for long periods of time.

Bottom Line:

Skeletal fluorosis is a painful disease that may change bone structure in severe cases. It’s particularly common in some regions in Asia where groundwater is very high in fluoride.

Does Fluoride Have Any Other Harmful Effects?

Fluoride has been controversial for a long time (22).

Numerous websites claim it is a poison that may cause all sorts of health problems, including cancer.

Here are the most common health issues that have been associated with fluoride and the evidence behind them.

Bone Fractures

Some evidence indicates that fluoride can weaken bones and raise the risk of fractures. However, this only happens under specific conditions (23).

One study looked at bone fractures in Chinese populations with varying levels of naturally occurring fluoride. Fracture rates increased when people were exposed to very low or very high levels of fluoride for long periods of time (24).

On the other hand, drinking water with around 1 ppm of fluoride was linked to a decreased risk of fractures.

Bottom Line:

Very low and very high intakes of fluoride through drinking water may increase the risk of bone fractures when consumed for a long period of time. Further research is required.

Cancer Risk

Osteosarcoma is a rare type of bone cancer. It usually affects the larger bones in the body and is more common in young individuals, especially males (25, 26).

Multiple studies have researched the connection between fluoridated drinking water and osteosarcoma risk. Most have found no clear link (27, 28, 29, 30, 31).

Yet one study reported an association between fluoride exposure during childhood and an increased risk of bone cancer among young boys, but not girls (32).

For cancer risk in general, no association has been found (33).

Bottom Line:

There is no conclusive evidence to suggest that fluoridated water increases the risk of a rare type of bone cancer called osteosarcoma, or cancer in general.

Impaired Brain Development

There are some concerns about how fluoride affects the developing human brain.

One review examined 27 observational studies mostly conducted in China (34).

Children living in areas where fluoride was present in high amounts in water had lower IQ scores, compared to those living in areas with lower concentrations (34).

However, the effect was relatively small, equivalent to seven IQ points. The authors also pointed out that the studies reviewed were of insufficient quality.

Bottom Line:

One review of observational studies mostly from China found that water with high amounts of fluoride may have a negative effect on children’s IQ scores. However, this needs to be studied much further.

Water Fluoridation Is Controversial

Adding fluoride to public drinking water is a decades-old, controversial practice to reduce cavities (35).

Water fluoridation started in the US in the 1940s, and about 70% of the US population currently receives fluoridated water.

Fluoridation is rare in Europe. Many countries have decided to stop adding fluoride to public drinking water due to safety and efficacy concerns (36, 37).

Many people are also skeptical about the effectiveness of this intervention. Some claim that dental health should not be handled by “mass medication,” but should be dealt with at the individual level (36, 38).

Meanwhile, many health organizations continue to support the fluoridation of water and say that it’s a cost-effective way to reduce dental cavities.

Bottom Line:

Water fluoridation is a public health intervention that continues to be a subject of debate. While many health organizations support it, some argue that this practice is inappropriate and equates to “mass medication.”

Take Home Message

As with many other nutrients, fluoride appears to be safe and effective when used and consumed in appropriate amounts.

It can help prevent cavities, but ingesting it in very large amounts through drinking water may lead to serious health issues.

However, this is mainly a problem in countries with naturally high fluoride levels in water, such as China and India.

The amount of fluoride is tightly controlled in countries that intentionally add it to drinking water.

While some question the ethics behind this public health intervention, fluoridated community water is unlikely to cause any serious health problems.