A prominent independent network of researchers recently examined every available study on water fluoridation and found that the practice does not reduce cavities.

The Cochrane Collaboration, a  global independent network of researchers, professionals, and patients, narrowed the review down to the most comprehensive, well-designed and reliable papers, before analyzing and publishing their conclusion.

According to Newsweek:

“The review identified only three studies since 1975—of sufficient quality to be included—that addressed the effectiveness of fluoridation in the population at large. These papers determined that fluoridation does not reduce cavities to a statistically significant degree, says study co-author Anne-Marie Glenny, a health science researcher at Manchester University in the United Kingdom.

The scientists also found “insufficient evidence” that fluoridation reduces tooth decay in adults (children excluded).

From the review, we’re unable to determine whether water fluoridation has an impact on caries levels in adults,” Glenny says.”

 Trevor Sheldon, dean of the Hull York Medical School in the United Kingdom, conducted a review of water fluoridation in 2000. Sheldon concluded that the process is not effective. “I had assumed because of everything I’d heard that water fluoridation reduces cavities but I was completely amazed by the lack of evidence,” he told Newsweek. “My prior view was completely reversed.”

Sheldon points out that some studies have actually shown that when water fluoridation was ceased, cavities went down a small percentage among schoolchildren.  This includes a 2001 study of two British Columbia communities that was included in the Cochrane review.

The Cochrane team also found that most studies confirming the effectiveness of fluoridation were completed prior to the widespread use of dental products such as mouth rinses and toothpastes. The study did find evidence that fluoridation was linked to a 26 percent decrease in cavities. However, this study was also done before the growth of modern dentistry. The researchers write, “We have limited confidence in the size of this effect due to the high risk of bias within the studies and the lack of contemporary evidence.”

Critics have long argued that any benefits of fluoride are only effective when applied topically, directly to the teeth. This would make water fluoridation largely a waste of resources. Moreover, exposing the internal organs to fluoride might actually be harmful to health. The possibility of harmful side effects from water fluoridation is still heavily debated.

In early June, the Health Research Board (HRB) completed an in-depth review of the effects of water fluoridation. The review was conducted at the behest of the U.S. Department of Health. After examining all internationally peer-reviewed papers on the topic of fluoride and health effects from 2006 to 2014, the HRB “found no definitive evidence that community water fluoridation is associated with positive or negative systemic health effects.”

Both the HRB review and the Cochrane review concluded that the majority of studies on fluoride, either for or against, were significantly flawed. The researchers found that around 70 percent of the studies did not account for conflicting factors, including sources of fluoride beyond tap water, diet, and ethnicity.

Despite the new findings from the Cochrane Review the U.S. Center for Disease Control and Prevention (CDC) stands by their support of water fluoridation.  Barbara Gooch, a dental researcher with CDC’s Division of Oral Health, told Newsweek that the review does not reduce the government’s “confidence in water fluoridation as a valuable tool to prevent tooth decay in children as well as adults.”

The new data comes just months after the U.S. Department of Health and Human Services released a report recommending water fluoridation levels be lowered.

The HHS released their final Public Health Service (PHS) for fluoride, calling for a change from the recommended 0.7 -1.2 milligrams per liter to a maximum of 0.7 milligrams of fluoride per liter of water.

The HHS says the change is in response to growing cases of dental fluorosis, which causes yellowing and pitting of the teeth. A 2010 U.S. National Health and Nutrition Survey found that approximately 41% of 12-15 year olds suffer from dental fluorosis, a consequence of fluoride overexposure. The Cochrane review also concluded that water fluoridation is leading to an increase in dental fluorosis.

For more on the history of Fluoride, health issues, and conflicts of interests with the CDC, check this article.