Fluoride Research Papers

Source: OECD.Stat/Dental Health

Chart updated on June 15, 2016. An earlier version of this chart incorrectly listed Australia and Chile as having non-fluoridated water. The water in both countries is fluoridated.

Moreover, fluoride itself may be dangerous at high levels. Excessive fluoride causes fluorosis—changes in tooth enamel that range from barely noticeable white spots to staining and pitting. Fluoride can also become concentrated in bone—stimulating bone cell growth, altering the tissue’s structure, and weakening the skeleton.

Perhaps most worrisome is preliminary research in laboratory animals suggesting that high levels of fluoride may be toxic to brain and nerve cells. And human epidemiological studies have identified possible links to learning, memory, and cognition deficits, though most of these studies have focused on populations with fluoride exposures higher than those typically provided by U.S. water supplies.

The Bottom Line

Comments by Philippe Grandjean, adjunct professor of environmental health, Harvard T.H. Chan School of Public Health:

“We should recognize that fluoride has beneficial effects on dental development and protection against cavities. But do we need to add it to drinking water so it gets into the bloodstream and potentially into the brain? To answer this, we must establish three research priorities.

“First, since dental cavities have decreased in countries both with and without water fluoridation, we need to make sure we are dosing our water with the proper amount of fluoride for dental medicine purposes, but no more.

“Second, we need to make sure fluoridation doesn’t raise the risk of adverse health effects. In particular, we need basic research on animals that would help us understand the mechanisms by which fluoride may be toxic to the developing brain.

“Third, we need to find out if there are populations highly vulnerable to fluoride in drinking water—bottle-fed infants whose formula is made with tap water, for example, or patients undergoing dialysis. If these individuals are at risk, their water must come from a source that is lower in fluoride.”

*This description of the Cochrane Collaboration’s findings in relation to water fluoridation and adult cavities is a clarification of the text in the print edition of the Spring 2016 Harvard Public Health, where this article originally appeared.

Nicole Davis is a science writer and communications consultant specializing in biomedicine and biotechnology. She holds a PhD in genetics from Harvard University.

A 2014 review paper in The Lancet Neurology identified a number of potential development neurotoxins in children, including manganese, fluoride, chlorpyrifos, tetrachloroethylene, dichlorodiphenyltrichloroethane and the polybrominated diphenyl ethers. One of these — fluoride — has continued to fuel a discussion since the article’s publication, as the water supplies of approximately 74 percent of the U.S. population have fluoridation. While the debate hasn’t yet risen to the same level as those over vaccines or global warming, some U.S. municipalities are reassessing the amount of fluoride in their water sources — or whether to fluoridate at all.

Journalists and communicators of all kinds should review the best research and the history of misinformation on the topic, and to avoid false balance — “he said, she said” characterizations — where the science remains definitive. In particular, not examining the dose in question — levels of fluoridation proposed or studied — can lead to faulty reporting.

History and state of the field

U.S. towns and cities started adjusting the amount of fluoride in their water about 70 years ago when research linked increased fluoride levels to improved dental health. Supporters of fluoridation state that it leads to healthier communities — and is economical and easy. While recognizing the important balance of effectiveness, dose and safety, the leading scientific and health groups are overwhelmingly pro-fluoridation. In April 2015, the U.S. Department of Health and Human Services recommended reducing the level of fluoride in drinking water to 0.7 milligrams of fluoride per liter of water. Its previous recommendation, outlined in its 1962 Drinking Water Standards, ranged from 0.7–1.2 milligrams of fluoride per liter of water.

Among the groups supporting fluoridation are the American Dental Association, the American Medical Association and the World Health Organization. The American Dental Association has called community water fluoridation “one of ten great public health achievements of the 20th century.” In a video posted to YouTube in December 2015, U.S. Surgeon General Vivek Murthy credited water fluoridation with helping reduce the prevalence and severity of tooth decay.

The CDC summarizes the chronology of the leading research by the U.S. National Academy of Sciences. The American Association of Dental Research held a special session during their 2014 annual meeting titled “Water Fluoridation: Safety, Efficacy and Value in Oral Health Care.” Outcomes from this meeting include general consensus that no scientific evidence exists to support the claimed negative health effects of fluoridation other than fluorosis — a change in the appearance of tooth enamel that can include white spots, staining and pitting. According to the CDC, dental fluorosis occurs when young children take in too much fluoride over a long period, when their teeth are forming under their gums.

Opposition background

Despite the evidence supporting the safety and efficacy of fluoridation, anti-fluoride critics have extended their influence and challenged public health experts. They claim that fluoride in drinking water has led to rising levels of fluorosis and can increase the risk of cancer. Some communities even reject fluoridation. For example, voters in Portland, Oregon did so in 2013, the fourth time in almost 60 years — overruling the city’s commissioners, who had agreed to fluoridate the city’s water supply. In January 2016, city officials in Durango, Colorado were debating whether to stop adding fluoride to city drinking water. In early 2016, residents of Healdsburg, California and those in Collier County, Florida were pushing their leaders to do the same thing.

Anti-fluoride groups such as the Fluoride Action Network have effectively used social media to convey their message, and some have lobbied the EPA’s Office of Water to “determine a scientifically based (not politically influenced) MCLG (maximum contaminant level goal) for fluoride.” However, the EPA and the Department of Health and Human Services base their current fluoridation recommendations on their own rigorous scientific assessments and on those of the National Academy of Sciences, all of which take into account the balance of dose, risk and health benefits.

The “Harvard study” and its limitations

In 2012, a review of studies linking high fluoridation levels with reduced IQ scores was published in Environmental Health Perspectives. Nicknamed the “Harvard study,” this report combined the results of 27 studies and found that “children in high­ fluoride areas had significantly lower IQ scores than those who lived in low­-fluoride areas.” The review concluded that the “results support the possibility of an adverse effect of high fluoride exposure on children’s neurodevelopment.” Experts writing in The Lancet criticized the study for a variety of serious flaws, however. Media outlets such as the Wichita Eagledug into the research, and found that 25 of the studies analyzed took place in China, where natural fluoride levels were much higher than those in controlled U.S. public water systems. But that did not stop Witchita officials and groups from using the study to help persuade voters to reject fluoridation.

In any discussion of the “Harvard study,” it might be noted that the Deans of the Harvard Medical School, Harvard School of Dental Medicine and Harvard School of Public Health have publicly expressed their support for fluoridation.

Useful studies for background

The following are authoritative research studies and accounts of fluoride; they serve as useful citations for communicators reporting on related issues:

  • A 2016 study published in the American Journal of Preventive Medicine, “Economic Evaluation of Community Water Fluoridation: A Community Guide Systematic Review,” offers a recent re-examination of the benefits and costs of community water fluoridation.
  • The National Research Council 2006 review “Fluoride in Drinking Water: A Scientific Review of EPA’s Standards.” This report suggests slightly lowered levels of fluoride but supports the use of fluoride for public health reasons.
  • A 2009 paper in the European Archives of Paediatric Dentistry, “Water Fluoridation,” presents decisive evidence for preventing tooth decay among children and states that “no association between adverse effects and water fluoridation has been established.”
  • A 2014 study in the American Journal of Public Health, “Community Water Fluoridation and Intelligence: Prospective Study in New Zealand,” seeks to clarify the fluoride-intelligence issue. It states that previous studies supporting the “lowered IQ” hypothesis have likely been subject to methodological errors, or “confounding.”
  • A 2007 study in the Journal of Dental Research, “Effectiveness of Fluoride in Preventing Caries in Adults,” finds evidence that fluoridation prevents cavities (caries) “among adults of all ages.”
  • A 1996 study in the Journal of Public Health Dentistry, “The Effectiveness of Community Water Fluoridation in the United States,” notes that the “data on effectiveness and safety are compelling.”
  • A 2000 research review by the University of York (U.K.) also presents a useful summary of academic literature.


Keywords: local reporting, safety, science

Last updated: January 12, 2016


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