Fluoride is a chemical commonly added to toothpaste to help prevent tooth decay. In many countries, it’s also added to the water supply for this reason.

However, many people are concerned about the potential harms from excessive fluoride intake.

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

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Fluoride is the negative ion of the element fluorine. It’s widely found in nature, in trace amounts. It occurs naturally in air, soil, plants, rocks, fresh water, seawater, and many foods.

Fluoride also 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 (1).

Fluoride is also important for preventing dental caries (cavities). This is why it’s a common ingredient in dental care products and is added to the water supply in many countries (2).

Summary

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

Fluoride can be ingested or applied topically to your teeth. Major sources of fluoride include (3):

  • Fluoridated water or salt. Countries like the United States, the United Kingdom, and Australia add fluoride to their public water supplies. In the United States, fluoridated water should ideally contain approximately 0.7 mg per liter. Some countries may fluoridate salt or milk as well (2, 4, 5).
  • Groundwater. Groundwater naturally contains fluoride, but the concentration varies. For example, some areas of India have dangerously high levels of fluoride in their water supply. This may lead to serious health problems (6).
  • 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 areas with non-fluoridated water supplies (1).
  • 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.
  • Dental care products. Fluoride is added to a number of dental care products on the market, such as toothpaste and mouth rinses.

Water fluoridation is controversial

Adding fluoride to public drinking water is a decades-old practice to reduce cavities, but it remains controversial — especially as research reveals more potential downsides to excessive fluoride intake.

Water fluoridation started in the United States in the 1940s, and over 70% of the U.S. population currently receives fluoridated water (7).

On the other hand, water fluoridation is fairly rare in Europe. Many countries have decided to stop adding fluoride to public drinking water due to safety and efficacy concerns, but it is available through other means — like fluoridated milk and salt, or fluoride supplements (8).

Many people are also skeptical about the effectiveness of fluoridated water. Some feel that dental health should be dealt with at the individual level, rather than through a community-wide intervention.

Additionally, fluoride appears to be more effective for cavities when applied directly in the mouth, rather than merely passing through it, as is the case with water (8, 9).

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

However, a 2015 review notes that most of the studies justifying the use of fluoridated water were conducted in the 1970s or earlier, highlighting a need for more recent research to support this widespread public health initiative (10).

Summary

Water fluoridation is a public health intervention that continues to be a subject of debate. While many health organizations support it, recent evidence suggests that targeted interventions may be more effective.

Dental caries, also known as cavities or tooth decay, are an oral disease. 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 (11).

When the replacement of minerals, called remineralization, doesn’t keep up with minerals lost, cavities develop.

Fluoride may help prevent cavities by decreasing demineralization, enhancing remineralization, and inhibiting bacterial growth and bacterial acid production in the mouth.

Fluoride may also help prevent bone fractures since it’s also associated with enhanced bone remineralization. However, more research is needed on this subject (1).

Summary

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.

However, there are some potential downsides to fluoride as well.

Fluorosis

Fluorosis occurs after prolonged exposure to excessive amounts of fluoride. There are two types: dental (affecting the teeth) and skeletal (affecting the bones).

Mild dental fluorosis, characterized by white spots on the teeth, is fairly common and presents only a cosmetic issue. More severe cases are less common, but are associated with brown stains and weakened teeth (10, 12).

Dental fluorosis only occurs during the formation of teeth in childhood, but the most critical time is under age 2.

Skeletal fluorosis is a bone disease that involves the accumulation of fluoride in the bone over many years. Early on, symptoms include stiffness and joint pain. Advanced cases may eventually cause altered bone structure and calcification of ligaments.

In animals, skeletal fluorosis from excessive fluoride is also linked to an increased risk of bone fracture (13, 14).

Skeletal fluorosis is particularly common in countries like India and certain other Asian and African countries where it’s primarily associated with the prolonged consumption of groundwater with high levels of naturally occurring fluoride, or more than 1.5 ppm (15).

Additional ways people in these areas ingest fluoride include burning coal in the home and consuming a particular type of tea called brick tea (16).

Skeletal fluorosis only happens when people are exposed to very large amounts of fluoride for long periods of time. It’s typically not an issue in countries with fluoridated water, as the fluoride content of water is tightly regulated in these countries.

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.

Multiple studies have researched the connection between fluoridated drinking water and osteosarcoma risk. Most have found no clear link (17, 18, 19).

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

Impaired brain development

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

A 2019 review found that excessive fluoride exposures in children were linked to cognitive deficits (20).

Another review of studies that included data on over 7,000 children had similar findings — noting that high fluoride exposure from water was associated with lower intelligence (21).

These two reviews, however, were both investigating areas where the fluoride level is naturally high.

Regardless, a small study on Canadian mothers and their infants found that formula-fed babies receiving formula made with intentionally fluoridated tap water had a lower “performance IQ” than breastfed babies in the study (22).

Despite this, the body of research as a whole doesn’t suggest that fluoride is neurotoxic at levels typically seen in developed countries (23).

However, excessive fluoride exposure in infants and children does warrant further exploration, especially in areas where fluoride levels are naturally high.

Summary

Potential downsides of fluoride include fluorosis, an increased risk of osteosarcoma, and impaired brain development in infants and children.

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 or other means may lead to serious health issues. However, this is mainly a problem in countries with naturally high fluoride levels in water, such as India.

The amount of fluoride is tightly controlled in countries that intentionally add it to drinking water. However, some evidence suggests that even controlled levels of fluoride in water may affect brain development in infants.

While fluoridated community water appears to be mostly safe, new research is needed to assess its effectiveness.