What is fluoride?
Fluoride is a group of compounds made from the ninth element in the periodic table, fluorine, plus one or more other elements. Fluoride compounds are found naturally in water, plants, rocks, air, and soil.
Water fluoridation is the process of adding fluoride to water. Fluoride concentrations in the public water supply are regulated. This is done to improve the health of our teeth. However, after a 1991 study on rats showed a possible link between fluoridated water and a type of bone cancer known as osteosarcoma, people began to question the safety of water fluoridation.
With so much false or misdirected information on the internet, it’s important to get the facts straight. Current research doesn’t support this relationship between fluoride and cancer.
We’ll break down the research so you can be more confident about the current consensus.
Why is fluoride added to water?
Dental cavities were a serious health problem in the United States in the early 20th century. They caused terrible pain, infections, and toothaches. A cavity was often treated by extracting the entire tooth.
After surveys were conducted across the country in the 1930s and ’40s, researchers realized that children who lived in areas with higher levels of naturally occurring fluoride (greater than 1 part fluoride per million parts water, or 1 ppm) had fewer cavities than those who lived in areas with low levels of fluoride.
This discovery was a huge breakthrough in dental health. In 1945, Grand Rapids, Michigan, became the first city in the world to adjust the level of fluoride in its water to 1 ppm. Fifteen years later, cavities in adolescent children living in Grand Rapids were reduced by nearly 60 percent compared to adolescent children in a Michigan city without fluoridation.
Scientists later learned that the optimal level of fluoride in the water to prevent tooth decay, and to avoid a cosmetic condition known as dental fluorosis, was 0.7 ppm.
Once community water fluoridation spread throughout the country, the average number of decayed, missing, or filled teeth in children declined 68 percent.
Fluoridated water has been shown to reduce cavities in adults by 20 to 40 percent.
Nowadays, the majority of the U.S. population served by public water systems uses fluoridated water.
The debate about water fluoridation stems from a 1991 analysis by the U.S. National Toxicology Program. The study found evidence that male rats given water with a high fluoride content for two years had an increased risk for a type of bone tumor called osteosarcoma. The association wasn’t seen in female rats, or in male or female mice.
A 2006 national case control study published by scientists at Harvard University found that boys exposed to fluoridated water had an elevated risk of developing osteosarcoma during their teenage years. This association wasn’t seen in girls. One theory is that fluoride may collect in the growing parts of bones (growth plates). This is also where osteosarcoma tends to develop during a growth spurt.
Though fluoride found in toothpaste and mouthwash is also part of this controversy, they are less debated. Unlike tap water, these products aren’t typically ingested. It’s also possible to purchase fluoride-free toothpastes.
Is there research that shows that fluoride causes cancer?
After these studies linking fluoride to bone cancer were released, researchers decided to further investigate.
After the 1991 animal study, researchers in New York decided to examine if bone cancer rates have increased since the introduction of fluoridation programs. But the study found no changes in bone cancer rates since the 1970s. There were also no differences in bone cancer rates between areas of New York City with fluoridation and areas without.
One limitation of this study is that it was difficult to precisely measure fluoride exposure on an individual level. This was especially true for people who may move around between fluoridated and non-fluoridated areas of the city.
A 2012 ecological study also concluded that water fluoridation had no effect on bone cancer rates in children and adolescents. A potential shortcoming of this study was its use of broad water fluoridation categories.
More recently, a 2016 study conducted in Texas examined a more detailed range of fluoride levels in public drinking water. This study also found no relationship between fluoridation and osteosarcoma, even after adjusting for age, sex, race, and poverty.
Another recent study looked at 2,566 cases of osteosarcoma and 1,650 cases of Ewing’s sarcoma (a rare bone tumor that also occurs in children) in Great Britain. It found no association between bone cancer risk and fluoride in drinking water. Though this study was conducted over a small area, it was the first of its kind done in Great Britain.
A closer look
For the studies that did show a link between fluoridation and bone cancer, it’s important to acknowledge their limitations. In the 1991 rat study, for example, levels of fluoride used in the study were much higher than what would be found in a community fluoridation program.
In the 2006 Harvard University study, there may have been a potential selection bias because of how hospitals were chosen in the study. Also, the number of cases of bone cancer within this age group would have been extremely small. This limits the statistical power of the study.
In 2011, results of the second part of the Harvard study were published. It compared fluoride levels in bones near osteosarcoma tumors to those in bones with other types of tumors. The researchers found no difference in fluoride levels between the different tumors.
The bottom line
Water fluoridation is considered the single most effective and economical public health measure to prevent tooth decay. During water fluoridation, fluoride levels are adjusted to an optimal level of 0.7 ppm.
In some places, fluoride concentrations in groundwater are naturally much higher than this level. They may even be more than 8 ppm. In these areas, community fluoridation programs actually work to lower the fluoride levels because of an increased risk of skeletal fluorosis.
A link was detected between fluoride and osteosarcoma in a couple of small studies. However, a multitude of follow-up studies and systematic reviews over the past 25 years have found no strong evidence that fluoride in drinking water causes cancer. The current consensus is that water fluoridation is safe and benefits dental health.
If you still have concerns about health risks associated with fluoride in dental products or your drinking water, speak with your doctor or dentist. If you want to learn more about the fluoride levels in your water, contact your local water supply agency or public utilities.