Fluoride in Water: Is There a Cancer Risk?

Fluoride is found naturally in water, soil, and some foods. It has been added to many public water supplies to help prevent tooth decay. Many decades after fluoride was first added to drinking water in parts of the United States, there’s still controversy around possible health effects, including cancer.

What is fluoride and where does it come from?

Fluorides are compounds that include the element fluorine combined with other elements.

Fluorides are found naturally in soil and water, although the levels can vary widely. Most natural water sources have some fluoride. Surface water sources (such as lakes and rivers) in the US have an average level of about 0.2 milligrams of fluoride per liter of water (mg/L), although levels can be much higher in some places than in others. Fluoride is also found in very small amounts in food from some plants and animals.

Once inside the body, fluoride is absorbed into the blood through the digestive tract. It tends to collect in areas high in calcium, such as the bones and teeth.

How are people exposed to fluoride?

The major sources of fluoride exposure for most people are water and other beverages, food, and fluoride-containing dental products, such as toothpastes or mouth rinses.

When was fluoride added to drinking water?

Water fluoridation began in some parts of the US in 1945, after scientists noted that people living in areas with higher water fluoride levels had fewer cavities. Starting in 1962, the United States Public Health Service (USPHS) recommended that public water supplies add fluoride to help prevent tooth decay.

Currently, about 3 out of 5 people in the US who are on public water systems have fluoride added to their drinking water. The decision to add fluoride to drinking water is made at the state or local level. The types of fluoride added to different water systems include fluorosilicic acid, sodium fluorosilicate, and sodium fluoride. All of these compounds release their fluoride molecules in water, allowing it to be absorbed in the human body.

How is fluoride in drinking water regulated?

Several governmental agencies play a role in regulating the amount of fluoride in drinking water. Regulations are in place to prevent health problems that can occur when fluoride levels are too high.

In public water systems

The USPHS recommends that fluoride levels in public water systems be kept at 0.7 mg/L to help prevent tooth decay while minimizing any potential health effects.

The US Environmental Protection Agency (EPA) drinking water standard requires that public drinking water systems keep fluoride levels below 4.0 mg/L. This is a legally enforceable requirement.

This regulation is mean to help decrease the risk of build-up of fluoride in the bones over time, which can lead to skeletal fluorosis. This condition can cause joint stiffness, pain, and weak bones with a higher risk of fractures in older adults.

The EPA has also set a secondary standard of no more than 2.0 mg/L of fluoride in drinking water. A secondary standard is a guideline, rather than an enforceable regulation. It means that public water systems must tell their customers if the fluoride level in their drinking water goes above 2.0 mg/L. If fluoride exceeds this level, it can cause dental fluorosis in children, a condition that can permanently stain or pit developing teeth.

State and local governments also have the option to cap the maximum level of fluoride allowed in drinking water to less than 4.0 mg/L.

In bottled water

The US Food and Drug Administration (FDA) sets bottled water standards. The amount of fluoride allowed in the bottled water depends on the amount of fluoride in the water source.

If the water source has low levels of fluoride, it might be added up to a maximum amount of 0.7 mg/L. This applies to imported bottled water and water bottled in the US.

If the water source for bottled water has higher levels of fluoride naturally, the maximum fluoride level allowed is 2.4 mg/L. Imported water can contain no more than 1.4 mg/L.

These regulations are in place to balance the benefits of fluoride for dental health with the need to prevent rare but real health problems from overexposure.

Does fluoride cause cancer?

Some studies have looked at the possible link between fluoride and cancer. The main type of cancer studied has been bone cancers such as osteosarcoma, because fluoride tends to build up in bone.

What do studies show?

Researchers try to determine if a substance causes cancer using 2 main types of studies:

• Studies in people (epidemiologic studies)
• Lab studies (studies done using lab animals or cells in lab dishes)

Often neither type of study provides conclusive evidence on its own, so both human and lab-based studies are reviewed when trying to figure out if something causes cancer.

Several lab studies have been done to look at the health effects of fluoride in rats and mice. Results from 2 studies showed a weak link between fluoride and bone cancer in male rats exposed to very high levels of fluoride. These results have not been supported by many other studies.

Studies in people have looked at the potential link between water fluoride levels and cancer. Many of these were retrospective studies that look back in time. They have compared, for example, the rates of cancer in a community before and after water fluoridation, or compared cancer rates in communities with lower levels of fluoride in drinking water to those with higher levels, either naturally or due to fluoridation. None of them found a strong link to cancer.

Although these studies provide some information, the findings are based on small numbers of people, which limits the conclusions that can be drawn from them. In general, the available research on water fluoridation and cancer is limited and has focused on osteosarcoma and not other cancers. Currently, there is no evidence to conclusively link fluoride to cancer, but the possibility cannot be ruled out. This is because there has not been enough research on this topic, especially for cancers other than osteosarcoma.

What do expert agencies say?

Several national and international agencies study substances in the environment to determine if they might cause cancer. In general, the American Cancer Society does not determine whether something should be considered a carcinogen (something that can cause cancer). Instead, we do look to other respected organizations for help with this.

The International Agency for Research on Cancer (IARC) deemed fluoride in drinking water “non-classifiable as to their carcinogenicity [ability to cause cancer] in humans.” They noted that the current evidence was inadequate to draw conclusions.

The Centers for Disease Control and Prevention (CDC) noted in a report in 1999 that “studies to date have produced ‘no credible evidence’ of an association between fluoridated drinking water and an increased risk for cancer.”

The National Research Council (NRC), part of the National Academies, issued a report titled “Health Effects of Ingested Fluoride” in 1993. Its conclusion was that “the available laboratory data are insufficient to demonstrate a carcinogenic effect of fluoride in animals.” They also concluded that “the weight of the evidence from the epidemiological [population-based] studies completed to date does not support the hypothesis of an association between fluoride exposure and increased cancer risk in humans.”

The NRC issued an update of the 1993 review in 2006. While the review included some new data, the results of this report were essentially the same: “On the basis of the committee’s collective consideration of data from humans, genotoxicity assays, and studies of mechanisms of actions in cell systems, the evidence on the potential of fluoride to initiate or promote cancers, particularly of the bone, is tentative and mixed.”

The European Scientific Committee on Health and Environmental Risks (SCHER) reviewed the evidence on water fluoridation in 2010. It concluded that the evidence linking fluoride in water to osteosarcoma was uncertain so that “fluoride cannot be classified as to its carcinogenicity.”

In 2011, California’s Carcinogen Identification Committee (CIC) reviewed the evidence and concluded that “fluoride and its salts has not been clearly shown to cause cancer.”

The general consensus among the reviews done to date is that there is no strong evidence of a link between water fluoridation and cancer. However, most noted that further studies are needed to help clarify the possible link.

Can I reduce my fluoride exposure?

If you’re concerned that you or your family may be exposed to too much fluoride, there are some things you can do.

Know the level of fluoride in your drinking water.

• If your drinking water comes from a public source, contact your local water system. Each public water system is required to provide its customers with an annual report on water quality. It lists the levels of certain chemicals in the water, such as fluoride. Community water systems are required to keep fluoride levels within acceptable standards or notify their customers.

• You can also contact the EPA’s Safe Drinking Water Hotline at 1-800-426-4791 for more general information about drinking water safety.
• If you get your drinking water from a private source, such as a well, you can have the fluoride levels tested by a reputable laboratory. Check with your local health department for a list of certified labs in your area.

If you live in an area with high levels of fluoride in the water, consider using alternate sources of drinking water, such as bottled water. Most bottled water has some fluoride, with natural spring waters tending to have the least. You can contact the bottler to find out about fluoride levels. There are also several methods to filter fluoride out of water, although these can be expensive.

Limit fluoride toothpaste for children.

• The CDC recommends that children under 6 years old use only a pea-sized amount of toothpaste for brushing. Do your best to make sure they do not swallow the toothpaste, as this can be a significant source of fluoride.
• For children under 2 years old, check with your child’s dentist before using fluoride toothpaste. Low- and no-fluoride toothpaste and other dental products are also available.