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Water fluoridation
The Canadian Cancer Society realizes that some Canadians may have questions about the health benefits and potential risks of being exposed to fluorides. We know that fluoride helps to prevent tooth decay, but some recent studies have raised fears that water fluoridation may be linked to an increased risk of osteosarcoma especially in boys. Although the balance of current evidence strongly suggests that it is not, the Canadian Cancer Society urges government agencies to work together to ensure that fluoride in drinking water is reduced to the lowest level required to optimize its health benefit.
Water fluoridation in Canada
Fluorides are chemical compounds. They are found in nature – in rocks and soil, in fresh water and in ocean water. In some communities, natural levels of fluoride in the water supply match the optimal level to prevent tooth decay. In many others, the level of fluoride is too low and has to be adjusted. In Canada, the optimal range for fluoride in drinking water suggested by Health is 0.8 to 1.0 milligrams per liter (mg/L).
Fluoridation itself is regulated at the provincial level, although the fluoridation of drinking water supplies is a decision that is made by each municipality. All provinces currently approve fluoridation. Two kinds of fluoride are added to water supplies in Canada. Hydrofluorosilicic acid is the most commonly used. Sodium fluoride may also be used to fluoridate drinking water but it is more expensive and more challenging to handle. Some people are concerned about the process by which the fluoride added to water is produced. Fluoride can be produced as a by-product of certain industries but these residues are not used directly. Every province and territory in Canada has mechanisms in place to ensure that the fluoride produced for water fluoridation meets a high standard of purity.
The Canadian Cancer Society urges government agencies to work together to ensure that fluoride in drinking water is reduced to the lowest level required to optimize its health benefit.
Know the fluoride level of your drinking water
The Canadian Cancer Society strongly supports Community Right to Know. We believe that people have the right to know about chemicals present in the environment to make knowledgeable decisions. This includes fluoride. Many jurisdictions in the United States inform consumers about the level of fluoride in their drinking supply. We urge the appropriate government agencies to work together with water suppliers to provide Canadians with this information as well.
The health impact of too much fluoride
Excessive fluoride is a concern in regard to young children. One possible result of taking in too much fluoride during the tooth-forming years is a condition called dental fluorosis. Excess fluoride affects the cells in the tooth that form enamel. As a result, the enamel of the tooth becomes hypomineralized and more porous. In most cases, the enamel exhibits faint white lines or streaks. In more severe cases, the surface of the enamel is stained yellow or brown and pitted
All sources of fluoride, not just drinking water, can contribute to dental fluorosis. According to the Canadian Dental Association (CDA) parents can help to control their children’s fluoride intake by:
- brushing or having their children brush their teeth with fluoridated toothpaste twice a day using a minimum amount of water to rinse the mouth after brushing
- brushing the teeth of children under 3 years of age, using only a smear of toothpaste
- supervising brushing or brushing the teeth of children younger than 6, using only a pea-sized amount of toothpaste
- encouraging the child to spit out, not swallow, excess toothpaste
The CDA does not recommend fluoride mouth rinsing for children under 6 years of age.
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Fluoride and cancer: the evidence
While decades of research have shown that water fluoridation helps to prevent tooth decay, there is also a smaller and significantly weaker body of scientific evidence about a potential relationship between exposure to high levels of fluoride in drinking water and cancer, particularly osteosarcoma in boys younger than 19. Osteosarcoma is a type of rare bone cancer . According to Canadian Cancer Statistics, one–hundred and seventy cases of osteosarcoma were reported in between 1997 and 2001, an average of 34 cases per year.
Numerous studies have shown no link between water fluoridation and an increased risk of osteosarcoma in either humans or rats. For example, the United States Food and Drug Administration evaluated the incidence of bone cancer for the period 1958-1987, using 40 international cancer registries. No relationship was observed between water fluoridation and bone cancer incidence. At least 7 additional studies, by groups including the Department of National Health and Welfare (now Health Canada), the Government of Canada, the United States Department of Health and Human Services and independent academic investigators have failed to observe a link between water fluoridation and the incidence of osteosarcoma.
However, a few studies have suggested a possible link. For example, a study on rats and mice conducted in 1990 by the National Toxicology Program of the United States found uncertain evidence that exposure to very high levels of fluoride in drinking water (100 or 175 parts per million, or milligrams per liter) increases the risk of osteosarcoma in male rats, but not in female rats or in male or female mice. However, subsequent studies have not confirmed this observation. Instead, the National Toxicology Program recently performed this experiment again using even higher levels of fluoride in drinking water (200 parts per million, or 200 milligrams per liter) and found no increase in osteosarcoma. It is important to recognize that the rats in this study were drinking water fluoridated at 200 times the recommended level in Canada.
In human beings, some early research showed a link between water fluoridation and an increased risk of cancer. However, this relationship disappeared when researchers controlled for socio-economic differences. More recently, an analysis led by Dr EB Bassin showed an increased risk of osteosarcoma in young boys (ages 6-8) consuming water that met the target level for fluoridation, relative to boys who consumed water containing 70% less fluoride. No such effect was observed in girls. The authors of the Bassin article acknowledge that their work has limitations, including a small number of study participants and potential misclassification. They admit that further research is needed to confirm their exploratory analysis.
The Bassin article is a preliminary analysis of 15-year effort to study fluoride and osteosarcoma by the Harvard School of Dental Medicine and collaborating organizations. The study’s principal investigator, Dr CW Douglass, is currently analyzing data gathered over a longer time period than was used in the Bassin article, providing a larger sample size. Dr Douglass reports that his study has not found the same association reported by Dr Bassin. Publication of his results will provide important further information as to whether and to what extent an association may exist between osteosarcoma and exposure to fluoride.
The Canadian Cancer Society will continue to monitor this issue and inform Canadians about the health impacts of the fluoride in their drinking water. At this time, the weight of the scientific evidence, as assessed by independent committees of experts and analysis of the findings of individual and combined studies does not support an association between water fluoridated at levels optimal for health and the risk for cancer, including osteosarcoma.
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Our position
The Canadian Cancer Society recognizes the importance of weighing the possible risks and the benefits for complex issues. On the basis of current evidence, it appears unlikely that water fluoridation increases the risk of osteosarcoma in humans. At the same time, the health benefits of water fluoridation have been proven, especially for people who have less access to dental care. As new research on the health impacts of water fluoridation becomes available, the Canadian Cancer Society will evaluate it thoroughly and keep Canadians informed.
We urge the governments of Canadato make sure people are aware of the fluoride levels in their drinking water and of any steps they need to take to avoid negative health impacts. We also ask government agencies to work together to ensure that fluoride in drinking water is reduced to the lowest level required to optimize its health benefit.
What we’re doing
The Canadian Cancer Society constantly monitors new research so we can inform Canadians. We will develop and revise our health messages and advocacy on water fluoridation as new information becomes available.
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More information
Our position on Community Right to Know
Health Canada’s position on fluoride
The Centers for Disease Control (United States) position on fluoride and fluoridation research
Canadian Dental Association’s answers to frequently asked questions about fluoride
The Canadian Pediatric Society’s Recommendations on the use of fluoride in infants and children Last modified on:
16 October 2008
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